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JET Manual 03Centrifugal Pumps

Version 1.1

JET Manual 03 Centrifugal PumpsInTouch Content ID# 4127826 Version: 1.1 Release Date: July 31, 2006 Owner: Well Services Training & Development, IPC

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Copyright © 2006 Schlumberger, Unpublished Work. All rights reserved.This work contains the confidential and proprietary trade secrets of Schlumberger and may not be copied or stored in an information retrieval system, transferred, used, distributed, translated, or retransmitted in any form or by any means, electronic or mechanical, in whole or in part, without the express written permission of the copyright owner.

Trademarks & service marks“Schlumberger,” the Schlumberger logotype, and other words or symbols used to identify the products and services described herein are either trademarks, trade names, or service marks of Schlumberger and its licensors, or are the property of their respective owners. These marks may not be copied, imitated or used, in whole or in part, without the express prior written permission of Schlumberger. In addition, covers, page headers, custom graphics, icons, and other design elements may be service marks, trademarks, and/or trade dress of Schlumberger, and may not be copied, imitated, or used, in whole or in part, without the express prior written permission of Schlumberger. A complete list of Schlumberger marks may be viewed at the Schlumberger Oilfield Services Marks page: http://www.hub.slb.com/index.cfm?id=id32083

An asterisk (*) is used throughout this document to designate a mark of Schlumberger.

Other company, product, and service names are the properties of their respective owners.

iiiJET 03 Centrifugal Pumps |

Table of Contents

1.0 Introduction 51.1 Learning objectives 51.2 Safety warning 5

2.0 Introduction to Centrifugal Pumps 73.0 Centrifugal Pump Main Components 11

3.1 Impeller 113.2 Wear plates 123.3 Wear rings 133.4 Shaft 143.5 Volute 153.6 Bearings, bearing frame, and stuffing box 15

3.6.1 Bearings 153.6.2 Bearing frame and stuffing box 15

3.7 Packing seals 163.7.1 Rope packing or jam-type packing 173.7.2 Mechanical seals 17

3.8 Lubrication system 183.8.1 Self-lubricating packing 183.8.2 Oil (RA45, RA56, RB23) 183.8.3 Grease 19

3.9 Power sources 203.9.1 Diesel drives 203.9.2 Electric drives 203.9.3 Power-takeoff (PTO) 203.9.4 Hydraulic drives 20

4.0 Centrifugal Pump Types 234.1 4x5 RA45 with open impeller 234.2 5x6 RA56 with open impeller 244.3 10x12 RA02 and RB02 with closed impeller 244.4 2x3x11 RB23 with closed impeller 24

5.0 Fundamentals and Pump Performance 275.1 System head 28

5.1.1 Total static head 28

5.1.2 Total head 295.2 Vortexing 295.3 Horsepower and efficiency 305.4 Net positive suction head and cavitation 30

5.4.1 Net positive suction head (NPSH) 305.4.2 Cavitation 31

6.0 Pump Operation 336.1 Rigging up 336.2 Centrifugal pump priming 336.3 Pumping with centrifugal pumps 34

7.0 Parallel and Series Operations 357.1 Parallel operation 357.2 Series operation 35

8.0 Piping Design 379.0 Centrifugal Pump Preventative Maintenance 3910.0 Servicing 41

10.1 Repacking procedure 4110.1.1 Lip type oil seals for RA45 and RA56 pumps 4110.1.2 Lip type oil seals for RB23 pump 4110.1.3 Rope packing for RB23 pump 42

10.2 Overhauling centrifugal pumps 4310.2.1 4x5 and 5x6 centrifugal pumps disassembly 4310.2.2 4x5 and 5x6 centrifugal pump assembly 48

11.0 Troubleshooting 5312.0 References 5513.0 Appendix—Performance Curve 5714.0 Check Your Understanding 59

iv | Table of Contents

5JET 03 Centrifugal Pumps |

1.0 Introduction

This training introduces you to one of the most common low-pressure pumps in the oilfield industry, the centrifugal pump.

1.1 Learning objectivesUpon completion of this training, you should be able to:

explain the function of a centrifugal pump•

identify the centrifugal pump’s various •components

describe how the centrifugal pump •operates

identify different pump models•

maintain and service the centrifugal pump•

troubleshoot common pump problems.•

1.2 Safety warningProper supervision is required during hands-on training. Request assistance from your supervisor if you are unfamiliar or uncomfortable with an operation.

To prevent possible hazardous situations during operations, everyone engaged in the service or repair of equipment must ensure the safety of personnel.

When working on the pump, follow the procedures in Well Services Safety Standard (WSSS) 4: Facilities and Workshops.

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6 | Introduction


2.0 Introduction to Centrifugal Pumps

Theory of operation

When whirling around a bucket full of water, the water stays in the bucket as long as the bucket is moving at a certain speed. The same force that keeps the water in the bucket is used in centrifugal pumps. If the bucket has holes in the bottom, the water squirts out of the holes as you whirl the bucket. With a centrifugal pump impeller rotating in water, the water is forced out from between the blades just as it would squirt out of the whirling bucket. The force that causes the water to leave the impeller (or bucket) is centrifugal force, which is how centrifugal pumps get their name.

Figure 2-1. Whirling Bucket

A centrifugal pump employs a centrifugal force to develop a pressure that moves a fluid. When the pump is full of fluid and the impeller begins rotating, the fluid follows the impeller blades. As the impeller speed increases, the centrifugal force moves the fluid toward the outer edge of the impeller blade. When the fluid moves away from the center of the impeller towards the outer edge, it creates a vacuum in the center of the impeller in much the same way as when you drink through a straw.

Figure 2-2. Impeller

As you suck the fluid using a straw, the fluid moves to the top of the straw. More fluid then enters the bottom of the straw to replace the fluid that moved to the top. The same action occurs in the pump. The fluid continues to move to the outer edge of the impeller and then out of the volute while new fluid moves into the vacuum in the center of the impeller. The faster the impeller rotates, the faster the fluid moves outward, increasing the flow rate.

Placing the impeller in a volute guides the direction of the liquid towards a controlled destination.

8 | Introduction to Centrifugal Pumps

Figure 2-3. Centrifugal Pump Parts

Figure 2-4. Centrifugal Pump

Volute

Bearings

Shaft

Impeller

BearingsFrame

Stuffing box

Figure 2-5. Cross Section of Centrifugal Pump

Most pumping applications involve pumping out of a tank positioned higher than the truck. This tank is usually 10-12 ft high. If we lose 2 ft of head, we will only have 8-10 ft of head to feed fluid into the pump, lowering the pump performance. When pumping out of a tank positioned lower than the pump, the pump performance is lowered significantly. Thus, lifting fluid with the pump reduces the discharge by an amount equal to the lifting distance.

If the fluid level is above the pump, the discharge pressure is increased by an amount equal to the distance above the pump.

It is important to keep the connections from the fluid supply to the centrifugal pump as straight and short as possible. The viscosity of the fluid will also affect the pump performance. For example, a fracturing fluid is pumped at a slower rate than water.

Fluid tank

Lifting distance

92 ft

102 ft

10 ft

Figure 2-6. Lifting Distance


102 ft

10 ft

112 ft

Figure 2-7. Lifting Distance Above the Pump

10 | Introduction to Centrifugal Pumps



3.0 Centrifugal Pump Main Components

3.1 ImpellerThe impeller is the rotating element in a centrifugal pump through which liquid flows. Energy is imparted to the liquid in the impeller.

Three types of impellers are available:

Open: Open impellers have vanes attached •to a central hub with relatively small shrouds (also called walls) or no shrouds.

Figure 3-1. Open Impeller

Semi-open: Semi-open impellers have a •shroud on one side only.

Figure 3-2. Semi-Open Impeller

Closed: Closed impellers have shrouds on •both sides to enclose liquid passages.

Figure 3-3. Closed Impeller

The following table displays examples of impellers with their related flow rates and pressures.

12 | Centrifugal Pump Main Components

Table 3-1. Comparative Analysis

The impeller rotation, either clockwise or counterclockwise, is determined by the rotation of the shaft when looking at the input or driven end of the shaft. You can change the direction of rotation by

reversing the volute•

installing the opposite impeller•

switching the hydraulic lines to the motor.•

Figure 3-4. Counterclockwise Rotation, Clockwise Rotation

3.2 Wear platesWear plates provide a wear surface and seal between the casing and impeller. Wear plates are located on either side of the impeller and are generally either solid steel plates or steel plates covered with rubber.

Figure 3-5. Wear Plates

For non-abrasive pumping services, all-steel wear plates are generally the best choice because they seldom require replacement. For abrasive pumping services such as cementing, use rubber-coated wear plates.

When pumping toluene, xylene, or other petroleum-based products, the use of all-steel wear plates or wear plates covered with 70-durometer Buna N rubber because these fluids cause the rubber on the wear plates to swell. This swelling will cause the pump impeller to stall or the rubber coating to come off the wear plates.

A worn plate will quickly cause the impeller to wear because the liquid flows in an uncontrolled, or turbulent, manner. Therefore, replace the wear plates when installing a new impeller. For optimum performance, the correct clearance between the impeller and the wear plates is 1/16in.

Shims are used to make fine adjustments to the clearance between the plate and impeller.

Shims are laminated and composed of layers. Layers can be removed or added for an exact fit.


Figure 3-6. Shims

Note:Removing shims moves the impeller closer to the wear plate. Adding shims moves the impeller away from the wear plate.

3.3 Wear ringsWear rings serve the same function as wear plates, but are used in centrifugal pumps that contain closed impellers (such as the RB 2x3x11). Wear rings are commonly made of brass.

Figure 3-7. Installing a Wear Ring

Figure 3-8. Wear Ring


Figure 3-9. Wear Ring Detail

3.4 ShaftThe centrifugal pump shaft supports the impeller. The shaft itself is supported with bearings. The shaft transmits the torque from a power source to the impeller where it is subjected to the following loads:

Figure 3-10. Shaft

Radial loads result from the impeller weight •and pressure differences around the impeller when it is moving in a liquid.

Axial loads result from the pressure •differences between the high and low pressure sides of the impeller.

Torque loads result from the inertia and •viscosity of the fluids being moved, and are transferred from the impeller to the shaft, through a keyway that is notched into the shaft and the impeller.

Even with all these loads, the impeller deflection must remain within the minimum clearance between the rotating and stationary components.

Note:The input rpm of the centrifugal pump should not exceed the manufacturer’s specified maximum rpm or severe damage may result.

In addition to these loads, the shaft can also be affected by abrasion in the sealing area. Some shafts have interchangeable sleeves where contact occurs. Shaft condition greatly affects the packing life. Scored shafts wear out packing quickly.

Centrifugal pumps come in two drive styles—keyed or splined. The keyed shaft is extended from the pump and is used for pumps driven by a drive shaft or coupling. Splined shafts do not extend past the mounting flange of the pump and are used where a hydraulic motor is mounted directly to the pump.

Figure 3-11. Examples of Centrifugal Pumps


3.5 VoluteThe centrifugal pump volute surrounds the impeller. The volute directs the fluid flow from the pump inlet to its outlet. The volute converts the velocity energy into pressure and also directs the flow of the fluid.

Figure 3-12. Volute

Volute design depends on

maximum output rates and pressures•

sense of pump rotation or the intended •rotation direction.

In some pumps, the volute can be used for clockwise (CW) and counterclockwise (CCW) rotation as in the RA45, RA56, and RB23 centrifugal pumps. The rotation sense can be determined by watching the pump from the driving end of the shaft.

The following table provides a general guideline for casings and their relationship with the flow rate and pressure.

Table 3-2. Flow Rate and Pressure Analysis

Note:The volute and frame are generally made from cast iron. Therefore, they should never be welded or brazed because heat will cause the volute to become distorted, warped, or cracked.

3.6 Bearings, bearing frame, and stuffing box

3.6.1 BearingsThe main function of bearings is to support the shaft. The shaft must be held and supported precisely. If the impeller is allowed to contact the volute, failure of the impeller, volute, wear plates, shaft, and keyway may result.

Bearings are lubricated with an oil bath (e.g., the RB 2x3x11) or grease through a grease nipple connection on the casing (e.g., the RA 4x5). The bearings for the RA56 and RB23 are the same, but those for the RA45 are slightly smaller.

3.6.2 Bearing frame and stuffing boxThe bearing frame contains the bearing lubrication system and the bearings that support the shaft on which the impeller is mounted.


Figure 3-13. Bearing Frame

A seal or packing contained in the stuffing box is located between the stationary casing and the rotating shaft. The stuffing box can either be incorporated in the centrifugal pump casing (e.g., the RB 2x3x11) or mounted separately (e.g., the RA 4x5).

Figure 3-14. Stuffing Box

The stuffing box and packing material of a centrifugal pump provide a seal against pump leakage along the shaft. Liquid can leak from a pump and air can leak into a pump. Pack the pump correctly to ensure that the pump works optimally. Worn or incorrect packing material causes the seal to fail and scores the shaft.

3.7 Packing sealsPacking material counteracts the effects of the fluid trying to leak along the shaft during pumping.

Figure 3-15. Packing Seals

The packing material can be either seal packings or oil seals. Seals are mounted in the stuffing box to

prevent pumping fluid from leaking out of •the pumping chamber along the shaft

prevent lubricating fluid from leaking out of •the stuffing box

prevent air from entering the pumping •chamber.

Packing materials must have the following features:

low coefficient of friction•

no abrasive effect on the shaft•

the ability to prevent excessive leakage.•

Schlumberger uses two main types of packing materials:

square braided rope packing rings, also •called jam-type, that are used on self-lubricating pumps

rubber oil seals, also called automatic or •mechanical type.


Note:The seals are not pure rubber, as rubber expands and degrades in the presence of oil and thus will not create a seal. Seals are normally made of a rubber compound such as viton.

3.7.1 Rope packing or jam-type packingRope packing is called jam-type packing because it is jammed into the stuffing box. It is adjusted periodically by tightening the nuts on a gland to preserve its sealing ability as it gradually wears down. Rope packing can be found in the Guinard and RB 2x3 pumps.

Figure 3-16. Rope Packing Seals

Rope packing in a centrifugal pump acts like a seal around the moving shaft, but only to the extent that it throttles leakage. The packing is in effect a bearing and must be lubricated as such. Lubrication comes from a slight leak through the packing or, in emergencies, from a saturant in the packing itself. If the packing is dry, it becomes hot, hardens, and then scores the shaft.

Over-tightened packing will burn up quickly and score the shaft, so it is important to pack the stuffing box properly. Typically, the ring next to

the gland in jam-type packing does most of the work because the mechanical pressure on the gland is greater than the friction along the rod.

There are other considerations that affect sealing, such as the packing shape, the material used and the stuffing box design.

Some common rope packing ring materials are

asbestos rope•

Teflon-coated rope•

graphite-coated rope.•

3.7.2 Mechanical sealsMechanical seals work by liquid pressure in the seal chamber which forces the mating faces together and provides a thin film of lubricant between them. The sealed fluid supplies the necessary pressure by forcing the packing against the wearing face. Mechanical seals are usually lubricated with oil from an external lubricating system such as an Alemite pump.

Caution:Do not over-tighten the jam-type or oil seals.

Figure 3-17. Mechanical Seals


Examples of pumps that use mechanical seals are

RA 4x5•

RA 5x6•

RB 2x3x11•

The sealing mechanism requires no gland nut adjustment.

Note:Adjusting the gland nut where mechanical seals are used will not stop a leak if one should occur. The gland nut is only there to help ensure that the mechanical seals do not work out of their bore.

Pumps using oil seals have enclosed lubrication systems, which makes them less susceptible to pressure loss. Pressure loss can occur with jam-type seals that are allowed to leak. Oil seals hold pressure from one side only and have one correct way of insertion.

3.8 Lubrication systemIf the packing is not lubricated, it will quickly burn up and score the shaft. Therefore, reliable operation of the packing lube is essential to protect the pump packing. During a job (even a short one), the failure of any part of the packing lubrication system can damage the pump packings, causing a job incident and loss.

Schlumberger uses three types of lubrication: self-lubricating packing, oil used for the RA45, RA56, RB23 pumps, and grease.

3.8.1 Self-lubricating packingSelf-lubricating packing is suitable for any pump that is pumping a clean non-abrasive fluid. The pumped fluid must be allowed to leak or flow through the stuffing box to cool and lubricate the packing. Do not run the pump without fluid or have the discharge closed, because this will reduce the flow of the fluid, preventing the packing from cooling off and lubricating.

The pump should be periodically checked to make sure lubrication is continuous. Lubrication occurs though a steady drip (2 to 3 drops per second) out of the stuffing box. Any interruption in the lubricating supply burns up the packing within minutes, causing severe pump damage.

3.8.2 Oil (RA45, RA56, RB23)Oil lubrication is best used for pumps that have low discharge pressure and require an enclosed lubrication system to prevent cavitation. This enclosed lubrication system permits the pumping of abrasive fluids, such as cement slurries. For optimum packing life, it is essential to properly lubricate the packing. Improperly lubricated packing can be completely damaged within seconds. Inadequate lubrication also causes heat generation, which shortens the packing life. The air-over-oil lube system is a high-reliability, low-maintenance lubrication system intended to replace the conventional Alemite systems in both cementing and stimulation services. The system is intended for use on new construction and retrofits on existing pumping equipment. The Air-over-Oil lube system relies on air pressure to force lubricant into the plunger packing. There are no moving parts to jam or fail. Refer to InTouch ID# 4027077 for more details on the air-over-oil lubrication system.


An air-operated pump, such as the Alemite pump delivers the lubricating oil to a divider block, e.g., the McCord divider, which in turn divides and delivers equal amounts of oil to each packing set. The divider is used in the lubrication system to ensure that each centrifugal pump will have a metered oil supply.

A blockage in any of the delivery lines causes the failure of the entire packing lubrication system because the McCord divider does not operate properly if any of its outlet ports is blocked. The outlet from the divider block is connected through a check valve to each individual stuffing box. From there, oil flows into the stuffing box and enters the lantern gland for even distribution to the packing. The packing lube pump has two sections—the air-motor section, which drives the pump, and the pump section.

Figure 3-18. McCord Divider Blocks

Schlumberger uses two types of McCord divider blocks: three-outlets and four-outlet types (Fig. 3-18). It is also possible to have up to six outlets by making up a proper valve configuration. Each divider block is made up of a base plate and metering valves. The 12S valve is a single outlet and the 24T is a dual outlet-metering valve.

3.8.3 GreaseGrease lubrication is a simple form of lubrication used on pumps that have a higher discharge rate and low pressure. The Schlumberger recommended lubricating grease has graphite or moly to reduce friction and has a very high melting point. Grease with a low

Table 3-3. Summary of Lubrication Types


melting point will melt and turn into oil, then leak away through seals and bearings.

3.9 Power sourcesSchlumberger uses centrifugal pumps that have a variety of drive mechanisms, chosen primarily for practical and economic reasons.

3.9.1 Diesel drivesDiesel-driven centrifugal pumps are generally found on small pressurizer skids and blenders. The pump is driven by an extended shaft, which is generally connected (for alignment purposes) by a drive coupling between the engine and the pump.

Figure 3-19. Diesel Drive

3.9.2 Electric drivesElectric-driven centrifugal pumps are used on the offshore recirculating cement mixers and batch mixers and generally take the form of pressurizer pumps, such as RA45 and RA56.

The shaft is usually extended and, as a safety mechanism, overload breakers are incorporated into the main power supply.

Figure 3-20. Electric Drive

3.9.3 Power-takeoff (PTO)Power-takeoffs are drive mechanisms coupled directly from the transmission of the engine. They are usually mounted on cementing units to drive the various centrifugal pumps, such as the RB23, RB45, or RB56 on the CPS-361 cementing skid.

Figure 3-21. Power-Takeoff Drive

3.9.4 Hydraulic drivesHydraulic drives power pressurizer centrifugal pumps such as the RA45-RA56 on cement pump units, recirculating mixers, and batch mixers. Although many are driven from the hydraulic system of the unit, some have an


independent power pack. The hydraulic pump of the unit drives a hydraulic motor, which is connected to the centrifugal pump using a close-coupled, splined shaft as a direct drive. The system is often fitted with an over-pressure relief mechanism that prevents any unwanted hydraulic pressure buildup.

Figure 3-22. Hydraulic Drive


4.0 Centrifugal Pump Types

4.1 4x5 RA45 with open impellerThe RA45 is used on Schlumberger units as a pressurizing and makeup pump. This centrifugal pump is designed with a 5-in suction and a 4-in discharge for both sand and cement pumping operations.

Figure 4-1. 4x5 RA45 With Open Impeller

It has two designs using different shafts:

standard extended shaft for conventional •drive

short shaft with an internal spline and with •hydraulic motor attached directly to the frame.

This type is the most widely used on Schlumberger units.

The RA45 generally uses mechanical oil seals. The impeller can rotate clockwise (CW) or counterclockwise (CCW). To determine the rotation direction, observe from the shaft towards the volute. If the volute increases in size, and travels around the impeller in a CW direction, then it is a CW rotation pump.

If the volute increases in a CCW direction, it is a CCW rotation pump. To change a CCW rotation pump into a CW rotation pump, reverse the volute. The suction side now becomes the frame mounting side and install a CW rotation impeller.

Figure 4-2. Impeller Rotates Clockwise

Figure 4-3. Impeller Rotates Counterclockwise

24 | Centrifugal Pump Types

4.2 5x6 RA56 with open impellerThe RA56 pump is similar to the RA45. It has a 6-in suction and a 5-in discharge and is used on recirculating mixers and paddle blenders. It is also used as a pressurizing pump on the CPS-361 and SLURRY CHIEFS.

4.3 10x12 RA02 and RB02 with closed impeller

The RA02 and RB02 pumps are used on blenders and PCMs and have a 10-in discharge and 12-in suction. The only differences between the RA02 and RB02 are the frame and suction adapters.

On the RB02 pump, the frame can be mounted on the right-angle gearbox. The suction adapter fits the suction duct from the blender mixer tank.

Figure 4-4. 10x12 RA02 and RB02 With Closed Impeller

On the RA02 pump, the frame is standard design. The suction adapter is a standard ASA150 flange for mounting as a deck pump on blenders.

4.4 2x3x11 RB23 with closed impeller The RB23 pump is used as a low-pressure mixing pump on Schlumberger cementing units. It has a 3-in suction, a 2-in discharge, and an 11-in impeller.

The RB23 has two designs:

One uses a standard extended shaft for •conventional drive.

The other has a short shaft with an internal •spline used to mount either the hydraulic motor or electric motor.

Rotation of the pumps can be either clockwise or counterclockwise.

Caution:Do not pump abrasive fluids using the RB23. The seals and shaft become damaged. Damage can also could occur between the wear plates and the impeller.

Caution:Do not run the RB23 pump without fluid. To run fluid continuously, install a small tube from the highest point of the volute that returns to the suction piping as far as possible from the pump. This will help keep the pump cool and aid in priming the pump.


Note:On the PTO-driven pump, the main engine must be shut down before the PTO can be engaged or disengaged.

26 | Centrifugal Pump Types



5.0 Fundamentals and Pump Performance

The flow developed by the centrifugal pump is controlled by the rotational speed of the impeller and gravity or density of the fluid being pumped. The faster the impeller rotates, the higher the velocity, or speed, the fluid has as it leaves the outer edge of the impeller. This means that the fluid will travel farther before stopping, which is why pump discharge pressures are always given in feet of head. Feet of head means that the pump will lift a column of fluid a given distance, in feet, straight up—regardless of what kind of fluid is being pumped. Thus, a pump that has a discharge head of 140 ft will lift a column of water or cement 140 ft. The discharge pressure gauge reading will be different but the discharge head, in feet, will be the same.

All centrifugal pumps are rated or sized based on a flow rate and feet of head discharge. These ratings are measured at the pump outlet, with water, under ideal conditions. The table below provides some typical ratings for Schlumberger pumps. These are not the maximum rates or pressures that the pump produces.

When the centrifugal pump is connected to a treating line, the performance is decreased because of the number of hoses, valves, elbows, and tees used to move the fluid to and from the pump.

A 4-in suction hose causes a pressure drop of 2.3 feet of head per 100 ft of hose at 5 bbl/min. A single 4-in pipe elbow restricts the flow of fluid in an amount equal to 10 ft of hose. A fully open butterfly valve has a restriction equal to 6.7 ft of hose. These numbers may seem small but when they are added together they become significant.

The pressure at any point in a vertical column of liquid is caused by the weight of the liquid, which exerts pressure.

W A T E R

0 ft

5 ft

10 ftFigure 5-1. Static Head

This pressure is directly related to the height of the column, which is called the static head and is expressed in terms of liquid feet. The static head corresponding to any specific pressure is dependent upon the weight of the liquid.

As the pump imparts velocity to a liquid, the velocity energy is transformed into pressure energy as the liquid leaves the pump. Therefore, the head developed is approximately equal to the velocity energy at the edge of the impeller.

Pump Model

Impeller rpm

Suction Head ft

Discharge Rate GPM

Total Head ft

Efficiency %

RA45 RA56 LaBour RB23

2200 500 27065

298 102 143 213 460 -------

65 60 70 + 10

+ 20 + 20 -------

2200 2200 3200

Table 5-1. Performance Analysis

28 | Fundamentals and Pump Performance

5.1 System headSystem head is the head that exists in a particular piping network at a particular flow rate. The pump performance is shown in the total head capacity curve of that particular pump.

The point on the head capacity curve where the pump operates is dependent upon the system head. When plotting a curve depicting system head versus flow together with a pump’s capacity curve, the intersection of these two curves is the performance of that pump.

0 100 200 300 400 500 600 700 800 900 1000 1100 1200

Operating Range

System Head 2

System Head 1

Head Capacity

Static Head

200

Hea

d

Figure 5-2. System Head

The system head is composed as follows.

5.1.1 Total static headTotal static head is the difference between the levels of the discharge and the suction liquid.

The static suction head is the difference in elevation between the suction liquid level and the pump centerline. When the liquid level is below the pump centerline, the static suction head is called a suction lift. The static discharge head is the difference in elevation between the discharge liquid level and the pump centerline.

Suction lift•

Suction lift shows static heads in a pumping system where the pump is located above the suction tank (static suction lift).

Static SuctionLift

Static DischargeHead

Figure 5-3. Static Suction Lift

Positive suction head•

Positive suction head shows static heads in a pumping system where the pump is located below the suction tank (static suction head).




Figure 5-4. Positive Suction Head

Pressure head•

Pressure head is the difference in pressures on the liquid surfaces:


The pressure head is added or subtracted from the system head depending on its condition. If there is a vacuum on the suction liquid level or a positive pressure on the discharge liquid level, then these heads are added to the system head. Likewise, if there is a positive pressure on the suction liquid level or a vacuum on the discharge liquid level, then these heads are subtracted from the system head. These pressures are converted into feet.

Friction head•

Friction head is the head required to overcome resistance to flow in the piping network. Entrance and exit losses are also included in friction head considerations.

Velocity head•

Velocity head is the energy of a liquid resulting from its motion at a particular velocity, which is the head required to accelerate the fluid.

5.1.2 Total headThe total head is the work (at a particular flow rate) that a pump must do in a pumping network for it to pump the fluid through the system. For any flow at any particular time in a piping network, the total head is equal to the system head.

In an existing system, the total dynamic discharge head can be found with a pressure gauge on the discharge line.

Total dynamic suction head is the static suction head plus the velocity head at the pump suction flange less the friction head. The pressure head is subtracted if there is a vacuum on the suction liquid level. The pressure head is added if there is a positive pressure on the liquid surface. In a current system, the total dynamic suction head is the gauge reading, at the pump suction

flange, corrected to psia (absolute pressure = gauge pressure + atmospheric pressure) and converted to feet of liquid, plus the velocity head at the point of the gauge attachment.

Total dynamic suction lift is the static suction lift less the velocity head at the pump suction flange plus the friction head on the suction pipe. The pressure head is added if there is a vacuum on the liquid surface; otherwise, the pressure head is subtracted if there is a positive pressure on the liquid surface. In an existing system, the total dynamic suction lift is the gauge reading, at the pump suction flange, corrected to psia and converted to feet of liquid, less the velocity head at the point of the gauge attachment.

To determine the total head (system head), attach pressure gauges on the immediate discharge and suction of the pump and follow the procedures described in the previous two paragraphs for existing systems. You can use the calculated total head to determine the pump’s operation by comparing it with the pump’s performance curve.

5.2 VortexingVortexing occurs when using centrifugal pumps and other pump types. The fluid that is being sucked into the pump’s suction side begins to rotate like a whirlpool. This is caused by the rotation of the fluid while flowing through the lines going to the pump: rotation of the impeller, configuration of the tank opening, and amount of hydrostatic head in the tank.

Vortexing becomes visible when the fluid level becomes low in the tank. During vortexing a column of air is inducted into the pump. The air will then accumulate at the highest point in the line after the pump, causing the pump to lose prime while pumping. To minimize vortexing, perform one of the following actions:


Install crossbars in the suction of the pump •and tank.

Float a large piece of wood over the suction •opening in the tank.

Lower the rate of the pump. (This option is •not always feasible.)

5.3 Horsepower and efficiencyHorsepower is the weight of the pumped liquid in a period of time multiplied by the total head.

Water horsepower (WHP) is the hydraulic horsepower delivered by the pump, which is defined as follows:

In Standard Oilfield units:

WHP = Water HorsepowerQ = Flow rate (gallon/min)Hr = Differential head (feet)SpGr =Specificgravity(S.I.)(1=water)

WHP (HP) =Q( ) × Hr(ft) × SpGrgal

min

3,960

3,960 = 33,000 HHP8.33ppg

The constant (3,960) is the number of ft-lb in one horsepower (33,000) divided by the weight of one gal of water (8.33 lbm).

In metric units:

WHP (kW) =

Q( ) × Hr(mtr) × SpGr m3

hr

376.5

Brake horsepower (BHP) is the actual horsepower delivered to the pump shaft, defined as follows:

BHP (HP) =

Q( ) × Hr(ft) × SpGrgalmin

3,960 × Eff= WHP

BHP

Brake horsepower is always greater than hydraulic horsepower because of the friction in the pump. Pump efficiency is the ratio of these two values.

Pump Eff = WHP

BHP

5.4 Net positive suction head and cavitation

5.4.1 Net positive suction head (NPSH)When pumping liquids, there are pressure losses as the liquid flows into the impeller. The losses are caused by:

increase in fluid velocity•

turbulence as the liquid strikes the impeller.•

NPSH is an analysis of energy conditions on the suction side of a pump, which will determine if a liquid will vaporize at the lowest pressure point in a pump.

The majority of centrifugal pump problems are a direct result of less than NPSH required to the centrifugal pump.

Note:While you will not be expected to calculate available NPSH, it is important to understand this characteristic of centrifugal pumps in order to avoid problems when laying and hooking up suction hoses and lines.


Although most factors of available NPSH are controllable, friction loss is usually easier than the others. Keep suction lines as short and straight as possible. The maximum flow rate for a 4-in suction hose is 7 bbl/min for a straight 12½-ft hose under ideal conditions. The maximum rate can drop with long lines, high lift, and many other conditions, which would indicate a lower rate. The higher the flow rate, the higher the friction loss, which results in air or vapor separation.

This is always complicated further by elbows, tees and other flow path alterations or restrictions, especially those located near the pump suction where they can set up uneven flow patterns or vapor separation, causing uneven filling of the impeller vanes. This can affect the hydraulic balance of the impeller and lead to possible cavitation, excessive shaft deflection or even breakage, and premature bearing and impeller retaining bolt failures.

5.4.2 CavitationCavitation is a frequently encountered problem when there is insufficient NPSH. Cavitation occurs in pumps when the pressure of the liquid being pumped is reduced to a value equal to or below its vapor pressure, and small bubbles move along the impeller blades to a higher pressure area where they rapidly collapse and implode. Therefore, if the pressure above the liquid is below its vapor pressure at that temperature, the liquid starts to evaporate. This is usually heard as a growling or rumbling sound, much like the noise you would hear if you were pumping gravel. The forces are sometimes high enough to cause small fatigue failures on the impeller vane surfaces. This damage is progressive during long pumping periods in this condition and the pitting and fatigue failures are referred to as cavitation erosion, which can sometimes be severe enough to cause vibration and ultimately shaft and bearing failure.

The pressure within the pump must not fall below the vapor pressure of the liquid at the pumping temperature. If the pumping pressure falls below the vapor pressure, the liquid begins to boil, causing cavitation.

The only way to prevent the undesirable effects of cavitation is to ensure that the

NPSHavailable to the system is greater than the NPSHrequired by the pump.

In summary, whenever a system offers insufficient NPSHavailable, increase the NPSHavailable or reduce NPSHrequired.

To increase NPSHavailable, take the following actions:

raise the liquid level•

lower the pump•

reduce the friction losses in the suction •piping

use a booster pump•

cool down the liquid to reduce the vapor •pressure Pv.

To reduce NPSHrequired, perform the following:

lower the pump speed•

use a double-suction impeller•

enlarge the impeller-eye area•

use an oversized pump•

employ an inducer upstream of the impeller.•


6.0 Pump Operation

6.1 Rigging upWhen rigging up the pumping unit, consider the rate, distance or pressure, and viscosity of the fluid you will pump. The maximum rate that can be safely sucked through a 4-in diameter hose is 7 bbl/min. If the pumping rate for the job is above 7 bbl/min, connect more hoses to the pump. Each pump’s maximum pumping rate is dependent on the suction and discharge pressures.

Piping connections to the pump should be as straight and short as possible. Each bend or change of flow direction becomes a restriction in the line, reducing the pump rate.

Grease the bearings of the pump and check the oil level according to the unit’s standard technical equipment maintenance checklist. The packing lube system must be full of lube and operational.

To provide maximum sealing, clean all connections on the suction side with a wire brush and lubricate the threads. It is important that the pump does not suck air into the system. A small amount of air leakage (4%) results in a large drop (43.5%) in pump performance.

Important:Use only soft hoses for discharge and hard hoses for suction. Refer to JET 01 Treating Equipment, Section 3.0, for more information.

Note:If the suction hose for the centrifugal pump is run from a dirty pit or tank, place a screen over the suction end of the hose to prevent any loose material from being picked up. Debris can easily clog or damage the pump.

6.2 Centrifugal pump primingA centrifugal pump is considered primed and capable of pumping when its suction lines are full of fluid. A pump that contains air in either the volute or lines turns without developing any flow. If there is no flow, pressure cannot be developed. Always prime the centrifugal pumps on cementing units or batch mixers before starting any job to make sure they are ready to pump.

Figure 6-1. Priming Pump with Higher Level Fluid Tank

A centrifugal pump is automatically primed when it sucks fluid from a tank positioned

34 | Pump Operation

above the pump. Gravity forces the fluid into the pump.

You must prime the pump if the fluid tank is placed at a lower level. To prime the pump, pull fluid using a positive displacement triplex pump through the centrifugal pump discharge side with fluid until the volute and suction lines are full of liquid.

If the packing lube system fails, air can be sucked into the pump through the packing or seals. This can cause a loss of prime in the pump.

Figure 6-2. Priming Pump with Lower Level Fluid Tank

Note:Air can enter the suction hose through loose unions, a hole in the hose itself, or a vortex in the tank causing the pump to lose prime and eventually to become damaged.

In a rig-up using more than one suction hose, it is easier to prime one hose at a time rather than all the hoses at once.

6.3 Pumping with centrifugal pumpsOnce the pump is rigged up and primed, it is ready to pump. If the pump has jam-type packing, check the proper flow of the lubricant. To check the flow, ensure that there is either packing lube or that the fluid being pumped is dripping out of the stuffing box.

Unlike a triplex pump, a centrifugal pump can be closed at the discharge side for a brief time without damaging the pump or piping. With the RA45 and RA56 pumps, you can close the discharge side for several minutes. On the other hand, you can close the discharge side of the RB23 and BJ pumps for only 15 seconds.

If the pumps are pumping against closed valves for a long period of time, the fluid inside the pump overheats and then burns the packing or seals. The pumps may also get hot enough to melt the grease out of the bearing housing. Correct operating procedures do not require the pumps to operate against closed valves for extended periods of time. Follow these guidelines when operating the pump:

Slow down the pump if it is not needed for •a few minutes.

When the pump is sucking fluid from a pit, •leave it running to maintain prime.

Maintain the required discharge pressure. •Any pump speed that produces more than the required pressure results in excessive pump wear and shorter life.

If the pump must be kept running with the •discharge side closed, rig up a bypass system that allows the fluid to return either to the tank or to the pump’s suction side. It is recommended to return the fluid to the tank. The fluid will heat up if it is returned to the pump suction, even at a much slower rate.


7.0 Parallel and Series Operations

Sometimes it is necessary to operate two or more pumps in conjunction with one another. The pumps will either be parallel or in series, depending on the requirements of the operation. The pumps must be similar in rate and pressure to operate in parallel or in series.

7.1 Parallel operationAn operation is called parallel if the discharge sides of two pumps are connected into the same outlet. The total rate is the sum of the two individual rates. The pressure does not change.

In a parallel operation, the discharge head is equal to that of one pump and the volume is equal to the total of the two pumps. Ensure that there is a continuous flow through the suction manifold of the centrifugal pumps. The discharge capacity of each pump must be the same to prevent one pump from moving fluid back through the second pump.

Figure 7-1. Parallel Operation

Example:Two pumps are to be operated together in parallel. Each has the capacity of 20 bbl/min at 100 ft of head.

Volume:

20 bbl/min + 20 bbl/min = 40 bbl/min

Discharge head = 100 ft

7.2 Series operationSeries operation occurs when one pump is pumping into the suction of another pump. The total pressure is the sum of the individual pressures. The rate does not change.

The volume is limited to the capacity of one pump. The discharge head is equal to the sum of the two pump’s discharge rate.

Due to the high incidence of seal failures in the second pump, this type of operation is not recommended.

Figure 7-2. Series Operation

36 | Parallel and Series Operations

Example:If two pumps are operated in series and each has the capacity of 20 bbl/min at 100 ft of head:

Volume = 20 bbl/min

Discharge head:

100 + 100 < 200 ft

Although the theoretical head for a series operation is 200 ft, the actual discharge head is always lower. This is because of the friction loss in the manifold between pumps and the different volumes and manifold arrangements.


8.0 Piping Design

The design of a piping system has an important effect on the successful operation of a centrifugal pump. Criteria such as pump design, suction piping design, suction and discharge pipe size, and pipe supports must be carefully evaluated.

Discharge pipe size is largely a matter of economics. The cost of the various pipe sizes must be compared to the pump size and power cost required to overcome the resulting friction head.

Suction piping design and size is of primary importance to the performance of the pump. The suction pipe must never be smaller than the suction inlet of the pump, and in most cases should be one size larger. Suction pipes should be as short and straight as possible.

Higher velocities than 5 to 8 ft/s increase friction losses and can result in troublesome air or vapor separation. Elbows and tees further complicate this process, resulting in uneven flow patterns, vibration, cavitation, and shaft deflection. Shaft breakage or premature bearing failure is the final result.

On pump installations with a suction lift, the suction pipe should be as horizontal with a slight slope upward. Ensure that there are no areas where air pockets can collect and cause the pump to lose its prime.

Run the piping from the pump to a point several feet away where the final connection is made to minimize excessive pipe strain on the pump nozzles. Always support the piping by attaching brackets to the main frame of the equipment. This reduces the weight the pump required to carry and the risk for hand traps when

performing pump maintenance. Always align the pipe and pump flanges.


38 | Piping Design


9.0 Centrifugal Pump Preventative Maintenance

Proper maintenance and repair is necessary for the safe, reliable operation of all Schlumberger equipment. To prevent possible service quality incidents or hazardous situations during operations, all employees must conform to the Well Services Safety Standards to ensure personal safety.

Keeping packing lubricated and adjusted

The packing lube system must be operating properly. The use of mechanical or lip type seals reduces maintenance. Perform the following to extend the life of jam-type packing.

Ensure adequate lubrication. In the case of •a centrifugal pump with a square braided packing, make sure that the fluid being pumped drips continually through the packing. Any interruption in the lubrication flow burns the packing and scores the shaft.

Do not over-tighten the packing nut. •Over-tightening results in a shorter packing life. To tighten a packing gland, tighten the two hexagon nuts 1/6 of a turn, then wait for about 10 minutes to allow the packing time to readjust itself and reduce excessive leakage. If excessive leakage persists after 10 minutes, retighten the two nuts. Make sure to tighten the two nuts the same distance to evenly distribute the load.

Loosen the packing gland in case the •centrifugal pump will be shut down for any length of time. This allows the packing to be thoroughly saturated by the pumping fluid when it is started up again and before it is tightened, reducing the chance of packing failure and grooved shafts.

Drain the packing lube system and clean •the reservoir periodically to prevent any objects from being sucked into the system.

Periodically add a small amount of •high-quality chassis grease to lubricate the bearings. The rear (farthest from the impeller) grease zerk is distorted to allow the air to escape. Grease the housing until grease comes out of the rear zerk.

Turn bearing seal lips inward to retain •grease in the housing. When installing new bearings that have shields, remove the shields before assembling the bearings onto the shaft. Shields prevent proper future lubrication of the bearings. Over-greasing can also damage the seals and cause premature bearing failure. The only way to properly inspect and lubricate the drive splines is to remove the hydraulic motor.

Note:Mechanical or lip-type seals are recommended. Rope packing is only used in emergency situations where mechanical seals are not readily available.

Excessive throttling shortens pump life

Never operate a centrifugal pump continuously near shutoff or zero capacity. It will shorten the pump’s life and increase downtime and maintenance. The difference between input horsepower and water horsepower is transferred to the liquid in the pump as heat. When only a small percentage of rated flow is allowed through the pump, the casing becomes

40 | Centrifugal Pump Preventative Maintenance

unable to dissipate the generated heat, which dangerously increases the liquid and pump temperature.

The hydraulic radial thrust becomes unbalanced when the pump is operating near shutoff and causes irregular deflection of the shaft. The pump becomes noisy and starts to vibrate excessively, which may lead to catastrophic shaft failure.

To relieve the pump of undue strain, extend a bypass line from the pump discharge back to the source of fluid. Place a throttle valve or an orifice plate in the bypass line.

Return sufficient flow to the pump so that it will operate at a capacity reasonably near its rating. Do not return the bypassed liquid to the suction line immediately upstream from the pump. Return discharge fluid back to the supply source below the liquid level to avoid air entrainment.

If excessive throttling at the discharge valve is required with the bypass line open, select a new rating for the actual system head and capacity requirements.

Throttling accelerates erosion when pumping abrasives

Pumping liquid that contains abrasive particles, such as cement slurry, causes erosion in the impeller and other pump parts. It also shortens the pump’s life.

When a pump is throttled to operate near shutoff, fluid with abrasive particles recirculates within the impeller and strikes the metal vane surfaces many times before it is discharged. This internal recirculation quickly erodes the impeller vane tips. Leakage clearances increase rapidly once the impeller is damaged.


10.0 Servicing

10.1 Repacking procedureIn order for the packing to work efficiently, the sleeve, shaft, bearings, and stuffing box must be in good condition. Replace any bent shafts. If the stuffing box bore is damaged due to pitting, a leak-free seal between the OD of the seal and the stuffing box housing is difficult to obtain. Use the correct type of packing for the application.

10.1.1 Lip type oil seals for RA45 and RA56 pumps

To remove and replace the lip type oil seals for the RA45 and RA56 pumps, complete the following steps:

STEP 01 Remove the old packing or oil seals from the stuffing box.

STEP 02 Inspect the stuffing box for cleanliness and wear. Clean as required.

STEP 03 Install the two oil seals with lips facing the impeller (10x12 will have three seals before the lantern gland).

STEP 04 Install the lantern gland. Ensure that the groove in the lantern gland is aligned with the oil hole in the stuffing box.

STEP 05 Install the next seal with the lip facing away from the impeller. This seal prevents air from entering the stuffing box and pump and allows lubrication to flow past its lip to lubricate the final seal.

STEP 06 Install the last seal with the lip facing the impeller in the same way as the first seals were installed. Some pumps require a small spacer behind the last seal. Use a spacer if the last seal is not flush with the rear of the stuffing box.

STEP 07 Install the packing gland or the stuffing box nut and tighten.

STEP 08 Make sure that the oiler is operating properly.

STEP 09 Start the pump and circulate water for five minutes.

STEP 10 Check for leaks and make sure that the oiler cycles while the pump is running.

Note:Further adjustments are not required during the seal’s life.

10.1.2 Lip type oil seals for RB23 pumpTo remove and replace the lip type oil seals for the RB23 pump, complete the following steps:

STEP 01 Remove the old packing or oil seals from the stuffing box.

STEP 02 Inspect the stuffing box for cleanliness and wear. Clean the stuffing box as required.

42 | Servicing

STEP 03 Install two oil seals with the lip facing the impeller.

STEP 04 Install the lantern gland and ensure that it is aligned with the oil hole in the stuffing box.

STEP 05 Install two more oil seals with lips facing the impeller as the first two seals were installed. See Step 3.

STEP 06 Install the spacer.

STEP 07 Install the packing gland with the flat side toward the spacer.

STEP 08 Tighten the nuts to 8 to 12 ft-lb.

STEP 09 Make sure that the oiler is operating.

STEP 10 Start the pump and circulate water for 5 minutes. Check for leaks and make sure that the oiler cycles while the pump is running.

STEP 11 Further adjustments are not required during the seal’s life.

10.1.3 Rope packing for RB23 pumpTo remove and replace the rope packing for the RB23 pump, complete the following steps:

STEP 01 Remove the old packing. Aim the packing hook at the bore of the stuffing box to keep it from scratching the shaft. Clean thoroughly so that the new packing does not hang up.

STEP 02 Check for bent shaft, grooves, or shoulders. If the neck bushing clearance in the bottom of the box is large, use a stiffer bottom ring or replace the neck bushing.

STEP 03 Install a dial indicator on the shaft and rotate it to check for any bending. If the run-out exceeds 0.003 in, straighten or replace the shaft. Check the condition of the bearings and the impeller balance. If any bending or wear exists, the pump vibrates and the packing fails prematurely.

STEP 04 To determine the correct packing size to install, measure the stuffing box bore and subtract the shaft diameter, then divide by 2.

STEP 05 Wind enough packing to fill the stuffing box around a rod of the same size as the shaft. Supporting the rod in a vise makes this task easier. Cut through each turn of the packing while it is coiled around the rod. Place each turn on a clean piece of paper, then roll it out with a pipe as you would use a rolling pin when making a pastry.

STEP 06 To have packing rings with parallel ends, cut the packing while it is wrapped around the rod. When the packing is cut while stretched out straight, the ends and gap will be at an angle, which is a problem when installing the packing. To install packing that has been cut at an angle, squeeze it into the top of the gap and ring and prevent it from closing.

STEP 07 Slide the ring off the rod sideways, especially lead-filled and metallic types to avoid distorting the molded circumference by breaking the ring at the gap.

STEP 08 Using a split wooden bushing, install the first turn of packing, then force it into the bottom of the box by tightening the gland against the bushing.

STEP 09 Stagger the packing ring joints so that they are not lined up together to ensure


that oil does not flow through the packing once it is installed.

STEP 10 Install the packing so that the lantern ring lines up with the flush or cooling liquid opening. Remember that this ring moves back into the box as packing is compressed. Leave space for the gland to enter.

STEP 11 Snug the gland nut up using a packing wrench. Back off and retighten the gland nut to finger tight. Allow the packing to leak for 15 minutes when first running the pump. Tighten the packing slowly to allow it to settle before readjusting to achieve the 2 to 3 drops per second lubrication flow through the packing.

STEP 12 Tighten each hex nut and wait 10 minutes for the packing to readjust itself before tightening the nuts any further. The packing should leak 2 to 3 drips per second with the pump shaft running close to optimum speed.

When preparing to pump latex or other fluid where no leakage can be tolerated, use the special graphite packing. Slowly tighten the packing until the leak stops. If the latex leaks into the packing area, continue to tightening the packing until the leak stops. This may cause the packing to smoke. Do not be alarmed, since the packing is rated to 800 degF, and as soon as the latex burns off the sealing surface, the smoking stops.

10.2 Overhauling centrifugal pumpsTo safely make repairs to centrifugal pumps, be sure that you wear the following personal safety gear:

steel-toed boots•

hard hat•

Nomex coveralls•

gloves•

safety glasses or goggles•

dust mask (if required).•

You will need the following tools:

2 heavy screwdrivers or thin pry bars•

rubber mallet•

socket set•

Allen key set•

spanner set•

12-in pipe wrench•

chisel or punch•

small hammer•

pliers.•

10.2.1 4x5 and 5x6 centrifugal pumps disassembly

To disassemble the 4x5 and 5x6 centrifugal pumps, complete the following steps:

STEP 01 Remove the motor retaining bolts that attach the hydraulic motor to the pump frame. For shaft-driven models, remove the drive shaft flange bolts or coupler set screws.

STEP 02 Carefully pull the hydraulic motor from the frame. Do not remove the hydraulic hoses. If the hoses must be removed, mark and cap the hoses, then plug them. For shaft-driven models, carefully pull the drive shaft or coupler back from the pump.

STEP 03 Tie the motor or drive shaft securely to the frame of the unit out of the way to prevent it from falling.

STEP 04 Remove the oiler line and lay it aside. Place a cap on the oiler to prevent any leakage.

44 | Servicing

Figure 10-1. Removing Bolts

STEP 05 Remove the bolts attaching the base support to the frame.

STEP 06 Remove the bolts holding the pump housing to the volute and mark the pump housing and volute so that they can be reinstalled in the same position.

Caution:The impeller blades can be extremely sharp from wear by fine abrasive fluids. Use extreme caution.

Figure 10-2. Marking Pump Housing and Volute

Figure 10-3. Using Pry Bars to Pry Evenly

STEP 07 Remove the pump assembly from the volute and place it on the workbench. It may be necessary to use pry bars to evenly pry the wear plate out of the volute.

Important:Do not use a hammer to remove the pump assembly.

Figure 10-4. Removing the Pump Assembly from the Volute

STEP 08 Remove the antirotation lock screw from the retaining stud by inserting an Allen wrench and turning 3 to 4 turns until it no longer makes contact with the impeller.


Figure 10-5. Removing the Anti-Rotation Lock Screw

STEP 09 Remove the impeller retaining bolt and the impeller lock.

STEP 10 Remove the impeller from its slip-fit position on the shaft. Cement buildup may make this difficult. If necessary, insert two pry bars underneath the impeller 180 degrees apart.

Caution:Use caution not to tear the rubberized coating of the backing plate. If the impeller cannot be removed, remove the bearing retainer bolts, then slide up the assembly to create a gap between the back plate and the impeller. Insert two equally thick steel bars between the impeller and the backing plate.

Figure 10-6. Removing the Impeller

Figure 10-7. Inserting Pry Bars

Warning:Do not attempt to hold the impeller with your bare hands.

46 | Servicing

Figure 10-8. Do Not Hold Impeller with Bare Hands

STEP 11 Remove the keyway and the two nuts from the rear of the back wear plate, and use two heavy screw drivers to separate the wear plate from the pump frame.

Figure 10-9. Removing the Keyway

Figure 10-10. Seperating the Wear Plate

STEP 12 Remove the lubricator fitting from the stuffing box and mark the stuffing box to the frame.

Figure 10-11. Marking Stuffing Box to the Frame

STEP 13 Lift the stuffing box out of the frame.


Figure 10-12. Lifting the Stuffing Box

STEP 14 Use a hammer and a punch to remove the cap from the locking assembly, applying light pressure to the cap.

Figure 10-13. Removing the Cap

STEP 15 Remove the four bolts and nuts from front bearing retainer bars.

Figure 10-14. Removing Bolts and Nuts

STEP 16 Using a hammer, lightly tap the shaft and bearing assembly out from the housing. The shims will fall on the ground. The shims will be used later to provide proper head space on the impeller.

Figure 10-15. Taping Shaft and Bearing Assembly

STEP 17 To replace the bearings, pry the locking washer tang out of the slot in the bearing retainer nut.

48 | Servicing

Figure 10-16. Replacing the Bearings

Figure 10-17. Pressing Rear of the Shaft

STEP 18 Press off the rear of the shaft. Clean and inspect the shaft for any signs of damage. Replace shafts that have any grooves or worn areas more than 0.01in (0.254mm) deep.

STEP 19 Remove the oil seals, lantern gland, spacer and snap ring from the inside of the stuffing box. Carefully clean and inspect the inside of the stuffing box for signs of damage. Rough spots can cause leaking seals, vibration, and even shaft and bearing failure.

Figure 10-18. Cleaning Parts from Inside the Stuffing Box

10.2.2 4x5 and 5x6 centrifugal pump assembly

To assemble the 4x5 and 5x6 centrifugal pumps, complete the following steps:

STEP 01 If installing new bearings with grease shields, remove the grease shields.

Figure 10-19. Removing Grease Shields

STEP 02 Lightly oil the shaft and press the new bearings and spacer onto it.

STEP 03 Install the lock and nut. Use a small amount of nylon thread-locking compound on the threads.


STEP 04 Carefully tighten the bearing nut without damaging the new shaft. An old impeller clamped into a bench vise works well to hold the shaft from rotating. Insert the shaft assembly into the pump frame.

STEP 05 Place the shims that were removed during disassembly under the front bearing snap ring, and slide the front bearing cap cover with seal onto the shaft.

Figure 10-20. Placing the Shims

STEP 06 Measure the shims with a dial caliper to ensure that both sides are of equal stack height.

STEP 07 Install the bearing retainer bars and bolts. It is not necessary to completely tighten these bolts until after the pump has been installed and the clearance between the impeller and front wear plate is set.

Figure 10-21. Installing Bars and Bolts

STEP 08 Install the new packing in the stuffing box in the following order:

Spacer (not used with new style stuffing 1. box

Note:The new style stuffing box, which does not use a spiral locks ring, does not require the first spacer.

Two oil seals (6679) with their lips facing 2. the impeller

Lantern ring3.

One oil seal (6679) with the lip facing 4. away from the impeller to prevent air pick up around the shaft

One last oil seal (6679) with the lip 5. facing the impeller.

50 | Servicing

Important:To install the stuffing box and packing properly onto the shaft, be sure to use a packing installation tool to avoid damaging the lips of the seals.

Figure 10-22. Lips of the Seals

STEP 09 Make up the stuffing box and tap it tight with a small punch. When installing the stuffing box, ensure that the lubricating holebhabhi with the grease fittings in the pump frame are in the same position as before.

Figure 10-23. Making the Stuffing Box

STEP 10 Reassemble the locking assembly and tighten the cap with the small pipe wrench. Install the pointed edge the lock toward the stuffing box nut right side. This will lock the nut in position.

Figure 10-24. Reassembling the Locking Assembly

STEP 11 Apply a very light coat of oil to the back of the wear plate and housing.

STEP 12 Align the rear wear plate with the two bolts for the retaining nuts and hand-tighten the nuts. This will allow the wear plate to center when the rotating assembly is inserted back into the volute.

Figure 10-25. Aligning the Rear Wear Plate


STEP 13 Install the impeller, key, slotted washer and lock (bolt). Be sure there is 1/8-in of key stick out to hold the slotted washer in position, then install the bolt. Use a small amount of thread locking compound to make sure that the bolt stays locked in.

Figure 10-26. Installing Impeller, Key, Washer, and Lock

Figure 10-27. Torquing the Lock

STEP 14 Torque the lock screw to the value shown:

PUMP ft-lb

N.m

4x5

5x6

75 ± 10

200 ± 25

100 ± 15

150 ± 20

Table 10-1. Torque Values

STEP 15 Install the lock screw to ensure that the lock (bolt) remains securely in place during operation. Use a small amount of thread locking compound. The lock screw should seat into an indention in the impeller bolt washer. It may become necessary to rotate the washer 180 degrees if it does not align with the indention at the proper torque.

52 | Servicing



11.0 Troubleshooting

The following chart lists various solutions to complaints resulting from the imperfect performance of a centrifugal pump.

Table 11-1. Troubleshooting

Troubleshooting

Symptom Solution

Pump will not prime. a. The pump is too high above the fluid source. b. The seals or packing are taking in air around the shaft. c. Too much clearance between the impeller and front wear plate. d. The pump speed is too slow. e. There is restriction or blockage in the suction. f. There are worn parts, impeller, wear plates, or volute. g. The impeller is loose on the shaft or the key is broken.

Low discharge pressure. a. There are worn parts, impeller, wear plates, or volute. b. There is restriction in the suction. c. The pump speed is too slow. d. There is too much clearance between impeller, and front wear plates.

Pump is noisy or vibrates. a. Cavitation b. Worn bearings c. Out of balance d. Loose mounting bolts e. Misaligned coupling f. Speed too high g. Broken impeller vane h. Aeration

Pump leaks around bolts at volute.

a. Wear plates are not sealing at the volute. b. There is excessive clearance between the volute and frame.

Pumps will not pump slurry. Slurry pumps will sometimes hold a normal discharge pressure; on hydraulically driven pumps, the hydraulic pressure will be normal when pumping water. As the slurry weight increases, the pump and hydraulic pressures become erratic, the pumps suddenly stops pumping, and the hydraulic pressure usually drops to 25% of normal. This condition can almost always be traced to defective shaft seals in the pump or seals that have been installed improperly with all the seal lips facing the impeller. The next-to-last seal in any mechanical seal arrangement must always face away from the impeller to prevent air pickup around the shaft.

To determine if the problem is a seal or a hydraulic problem, install the pump (on a hydraulically driven unit only) and observe the hydraulic pressure. If it is normal (usually 2,600 to 2,800 psi), then the problem is in the seals, not in the hydraulic system.


54 | Troubleshooting


12.0 References

Safety Standards for Well Services Operations (InTouch Content ID# 3038426)

WSSS 4—Facilities and Workshops (InTouch Content ID# 3313678)

WSSS 5—Location Safety (InTouch Content ID# 3313681)

WSSS 15—Lockout-Tag (InTouch Content ID# 3313691)

Centrifugal Pump Performance Manual (Engineering Version) (InTouch Content ID# 3015892)


56 | References


13.0 Appendix—Performance Curve

The performance of a centrifugal pump can be shown graphically on a characteristic curve that depicts the interrelationship of total dynamic head, brake horsepower (BHP), efficiency, and net positive suction head (NPSH) for a specific impeller and casing. The capacity curve shows the relationship between capacity and total head, while a system head curve is obtained by combining the friction head with the static head and any pressure differences in the pumping system.

Figure 13-1. Performance Curve

These curves are important for determining the type of pump you will need for a certain application, and can show the differences in the major classes of pumps:

Radial or volute

The head decreases gradually as the flow •increases.

The brake horsepower increases gradually •over the flow range with the maximum normally at the point of maximum flow.

Mixed flow

The head curve is steep.•

Brake horsepower remains constant.•

Axial

Head and brake horsepower both increase dramatically near shutoff.

ExampleThis example is a hypothetical engineering problem that illustrates the use of the performance curves shown in figure 13-1.

Assume that we have a piping network that requires a flow of 700 gal/min at a total head of 140 ft of water.

The maximum and minimum system heads are 500 gpm at 143 feet and 1,050 gal/min at 125 ft, respectively.

Figure 13-2. Performance Curve

A vertical line is drawn from the X-axis at 700 gal/min. A horizontal line is drawn from the left Y-axis at 140 ft. The operating point of the pump is the intersection of these two lines.

58 | Appendix I – Performance Curve

Looking at Figure 3-1, the intersection of these two lines falls on the 2,200 rpm capacity curve (total head curve). Therefore, the pump will be specified to operate at 2,200 rpm.

We also need to know the operating range of the pump, which is the entire capacity curve. In most cases, design restraints such as the system heads of the pipe system will determine the operating range.

For this example, we have calculated the maximum and minimum system heads, which will set the pump’s operating range. Vertical lines are drawn from the X-axis at 500 gal/min and 1,050 gal/min up to 143 and 125 ft. These lines should intersect the 2,200 rpm capacity curve.

Since the operating range of the pump is known, we choose the BHP that is required for the maximum operating point that will be encountered, which is 1,050 gpm at 125 ft of head. We look for the BHP line that is above our operating range (i.e., it does not intersect the 2,200 rpm capacity curve). In this case, the 50 BHP line completely contains our pump’s operating range. Therefore, a 50 BHP drive mechanism is specified.

The final information we obtain from the performance curve is efficiency. Efficiency can be used when you need to choose among several different pumps. Each efficiency curve depicts the boundary of the curve labeled efficiency. For our pump, the efficiency increases from 52% at the minimum operating point to 74% at the maximum operating point.

14.0 Check Your Understanding

59JET 03 - Centrifugal Pumps |

1. ____________ is the rotating element through which liquid passes in a centrifugal pump?A. wear ringB. impellerC. packingD. wear plate

2. Wear rings serve the same function as wear plates.A. trueB. false

3. Which of the following is used to make fine adjustments to the clearance between the plates and impeller?A. wear platesB. bearingsC. shimsD. packing

4. Bearings support the shaft.A. trueB. false

5. Which of the following drive mechanisms are used for the Schlumberger centrifugal pumps? Select four that apply.A. power-takeoffB. hydraulicC. electricD. dieselE. water

6. How do centrifugal pumps convert mechanical energy into hydraulic energy?A. by pushing air into the systemB. by pushing fluid into the systemC. by pushing mud into the systemD. by pushing gas into the system

7. How does the volute affect the velocity of energy of the liquid?A. converts it into pressureB. converts it into heat

8. Total head can be increased by increasing the rpm.A. trueB. false

9. Bearings support the shaft.A. trueB. false

10. Which of the following lubricate bearings? Select two that apply.A. oil bathB. gelC. greaseD. water

11. A centrifugal pump primes itself.A. trueB. false

60 | Check Your Understanding

12. Worn packing can cause the seal to fail.A. trueB. false

13. Rope packing is used in RB23 centrifugal pumps.A. trueB. false

14. Centrifugal pumps that use mechanical seals are _________, _________, and _________.A. RA 4x5B. RA 5x6C. RB10x12D. RB 2x3x11

15. Total suction head is the difference between the levels of the discharge and suction liquid.A. trueB. false

16. To minimize vortexing, perform which of the following (select three that apply):A. Install crossbars in the suction of the

pump and tank.B. Increase the pump rate.C. Lower the pump rate.D. Float a large piece of wood over the

suction opening in the tank.

17. The pressure within the pump must not fall below the vapour pressure of the liquid at the pumping temperature.A. trueB. false

18. To increase NPSH-A _________ , _________, and _________ .A. Raise the liquid level.B. Lower the pump.C. Use an oversized pump.D. Use a booster pump.

19. An operation is parallel when the discharge sides of two pumps are connected to the same outlet.A. trueB. false

20. You can operate centrifugal pumps continuously near shutoff or zero capacity.A. trueB. false

21. Pumping liquid that contains abrasive particles does not cause erosion.A. trueB. false

22. Air is mixed in the liquid being pumped as a result of (select all that apply):A. leaky suction linesB. improperly assembled stuffing boxC. inadequate seals on the suction lift

hook-upD. all of the above

23. Series operations are not recommended because of the high incidence of seal failures in the second pump.A. trueB. false

61JET 03 - Centrifugal Pumps |

24. When rigging up the centrifugal pump, take into consideration _________.A. rate B. distanceC. pressureD. viscosity of the fluidE. all of the above

62 | Check Your Understanding


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