centrifugal pump operation

CENTRIFUGAL-PUMP OPERATIONMYGAZEE ‘99

PP(T)SB PROPRIETARY DOCUMENT

Initial Start.

Starting a centrifugal pump for the first time can be a troublesomeexperience unless our plant crew has made a thorough check of the unit during andafter installation. There are probably more unusual accidents and troubles duringinitial starting of a pump than at almost any other time. Factors to be consideredin starting any centrifugal pump include pipe cleanliness, pump alignment, rotation,lubrication, position of valves, stuffing-box and mechanical seals leakage, effect ofchanges, bypass quantities, throttling of the discharge, and performance checks.

Pipe Cleanliness.

Multistage pumps, and many single-stage units, have close-clearance runningparts which must be protected from Abrasive particles often found in new pipingsystems. In one subsidiary, Rust particles which lodge in the running clearance of alarge barrel type feed pump caused the unit to seize, requiring expensive repairs andloss of pumping capacity during the ensuing shutdown.

Fig. 1. Temporary screen for pump inlet

This is but one example of damage caused by materials lodged in new piping.Many others could be cited because this problem is rather common. To reduce thepossibility of larger abrasive particles from reaching the pump, install a flat or conicalstrainer made up of No. 20 or 30 mesh window screen backed with ¼ inch meshscreen. Place the screen in the suction line as close as possible to the pump suctionnozzle. Install pressure gauges on each side of the screen so the pressure drop acrossit can be measured.

When starting the pump for the first time, watch both gages and whena pressure difference occurs between the two, indicating the screen is clogged, stopthe pump and remove the dirt and scale from it. When the screen is clean, replace it.



Continue cleaning and replacing, as necessary, until no further pressure drop occurs.For most installations, the screen should be used for at least 24 hrs before beingremoved.

Alignment.

Bring the pump to operating temperature by admitting liquid to the casing.Check the alignment,. Turn the pump over by hand. It should turn freely , withoutbinding, scraping, or making any noise. Inspect the pump footings to see that anydevice for expension of the casing are free and in good working condition.

Rotation.

Check the driver and pump rotation. When a polyphase driving motor isused, touch the starter button just long enough to make the motor turn a fewrevolutions. The pump shaft should turn in the direction of the arrow on the casing.

Figure 2a shows how to determine the direction of rotation of a horizontalcentrifugal pump. Stand at the driver end facing the pump. If the top of the shaftrevolves from left to right when viewed from this position the pump is said to rotateclockwise. A counter-clockwise pump turns in the opposite direction when viewedfrom the same point. For a vertical pump (Fig. 2b) look down at the top of thepump. If a point on the shaft revolves from left to right, when viewed from thisposition, the rotation is clockwise. When the shaft turns in the opposite direction itsrotation is counterclockwise.

Fig.2. Method of determining thedirection of rotation as specified by theHydraulic Institute (a) Horizontal pumpsand (b) Vertical pumps.



Pump Bearings.

Before any pump is started its bearings must be carefully inspected, cleanedand lubricated. With Oil-lubricated shoes sleeve bearings, thrust shoes (if used),and drain plug. Flush out the housing, oil piping, cooler, pump, and sump tank withkerosene, carbon-tetrachloride or safety solvent such as Klenco. Wash the bearingparts throughly and reassemble them the housing. Flush entire system withlubricating oil and allow it to drain to waste. This will ensure removal of any dirt,metallic, or waste particles present in the bearings or lube sysem. Replace the drainplug, caps, and other parts and fill the bearing as directed by the manufacturer or asgiven later in this article.

Grease-lubricated ball, roller, and needle bearings are usually packed withgrease at the factory before the pump is shipped. So no lubrication may benecessary before starting the pump. Check the condition of the grease by removingthe bearing housing cover. See that there is grease in the bearing. In general, do notadd any grease unless the pump manufacturer gives specific direction to do so. Anover-greased bearing may overheat soon after the pump is started. If it has,replace as directed later in this article.

Never start a pump equipped with Kingsbury-type thrust bearings withoutfirst pouring enough oil into the bushing to protect the thrust shoes. Extreme care

must be exercised with all types of bearings on pumps to see that they have enoughclean lubricant, Watch for contamination and for dirt picked up during shipment.

Thrust Bearings.

Figure 3 shows the steps in priming two designs of Kingsbury thrustbearings commonly used in centrifugal pumps. In the bearing in Fig.3a, fill thehousing with the correct. grade of oil until the level reaches the ring on the oil-levelgage. This resembles the gage shown in Fig. 4a. Remove the locking screw in thetop of the thrust-bearing cap and pour a liberal amount of oil into the bushing(Fig.3a). Replace the locking screw, making sure it fits into the bushing, to prevent itfrom rotating. Remove the vent plug at the top of the oil-pump body and pour inenough oil to wet the parts of the oil pump. Watch the oil level in the gage glass afterthe main pump starts. If the level stabilises too far below the marker, add oil until thelevel is ½ (12.5mm) to ¼ in. (6.5mm) below the ring.

The bearing in Fig. 3b and 3c does not have an integral oil pump. It is,however, filled in a manner similar to that described above for Fig. 3a. Be sure toreplace the locking screw tightly, to prevent the bushing from rotating. Theprocedures given here apply to one make of Kingsbury thrust bearing. To becompletely safe, check the pump instruction manual before flushing and filling thrustbearings of this type. The exact procedure may differ from that given here.



Fig. 3. Filling thrust bearings



Fig.4. Two types of commonly used oil level indicators.

Fig.5. Typical forced-feed lubrication system.

Sight Gage Glasses.

Figure 4a shows a bearing housing equipped with a typical sight gage glass. The bearing inFig.4b has a constant-level oiler. This device maintains a constant oil level in the bearing aslong as there is oil in its reservoir (oil bottle).

Lube-oil Systems.

Figure 5 shows a typical forced-feed lube-oil system for a horizontalmultistage centrifugal pump. It consists of an integral gear-type oil pump mountedwithin the thrust-bearing housing and taking its suction from an oil reservoir mountedbelow the pump shaft, as shown, a tubular oil cooler, piping, and pressure and levelgages. With this type of system, which is often used with large pumps having sleevebearings for the main shaft, clean and flush the bearings as outlined above, including



the sump-tank reservoir and the oil cooler. Pour oil into each bearing bushing and fillthe sump tank until it is ¾ full, or more. Important: Fill the supply line to thebearings so it will be full when the pump starts and there will be no delay in the oilreaching the bearings. The system supplies oil to both the bearings of the main pumpand its driver. Some pumps have a centrifugal-type impeller on the end of theirshaft, instead of a gear pump.

Fig.5b. An advanced (Pure) oil mist lubrication system console

Ball Bearings.

Almost all modern pumps use ball bearings to carry radial or thrust loads, orboth. (These are usually lubricated by an advanced pure or purge mistsystems- (fig.5b). The types of ball bearings used for centrifugal pumps includesingle-row deep-groove, double-row deep groove, double-row self-aligning, andangular contact types made in double-and single-row designs. They may be grease-or oil-lubricated, with oil being popular for the larger sizes. Figure 6a shows atypical double-type out-board bearing designed to take small axial thrust loadsduring pump starts and stops. It consists of two angular-contract ball thrust bearingsmounted back to back. A locknut and washer hold this bearing and the rotorassembly in correct position with respect to the rest of the pump.

Cooled Ball Bearings.

Where high temperatures are expected in bearing operation the race may besurrounded by a cooling jacket (Fig.6b). Water or another suitable liquid iscirculated through the jackets during pump operation.



Sleeve Bearings. In horizontal pumps these resemble the bearing shown in Fig. 3b, except

that a thrust collar is not fitted. A spherical seat permits the bearing bushing to alignitself with the shaft journal. Bearing linings are removable.

Vertical deepwell turbine pumps use either water-lubricated bearings(Fig.6b) or oil-lubricated bearings (Fig. 6d). With the first type the liquid pumpedserves as the lubricant and no supply from the surface is needed. Oil-lubricatedbearings are inside a shaft-enclosing tube and are fed oil from the ground surface bya lubricator mounted on or near the pump drive.

Lubricants.

Many manufacturers recommend a straight correctly refined turbine-typePetronas Jentram type neutral mineral oil for centrifugal pumps. Normally it shouldnot contain any free acid, chlorine, sulfur, or more than a trace of free alkali. Basedon tests by ASTM standard methods, the oil should at least have the physicalcharacteristics given in Table 2-1.

182.2 min60 SSU min

1.6 max75 sec max

165.5 min65.5 SSU min

-15 max75 sec max

Flash point, C............Saybolt Viscosity at 37.7CPour Point, C...........Steam Emulsion value

Paraffin-base oilNapthene-base oilOil characteristics

Table 2.1 Recommended lube-oil characteristics for centrifugal pumps

6 months3 months

6 weeks3 weeks

LowHigh

LowHigh

8 hour day:7-day week7-day week

24 hour day:7-day week7-day week

Greasing IntervalAmbient Temp. CPump Service

Table 2.2 Greasing Interval for Vertical ball-bearing Pumps



Grease-lubricated ball bearings are generally packed with lubricant beforeshipment. Over-greasing must be avoided because it is probably the most commoncause of overheating. Many pump manufacturers recommend a sodium-soap greasecarrying not less than 82 per cent of a high-grade filtered mineral oil having aviscosity of not less than 150 SSU at 37.7 C. The melting point must not be lessthan 148.8 C and The penetration at 25 C should be 275 to 330. In addition, thegrease should not separate on standing, nor should it form gum, become sticky,harden, decompose, or corrode. Check to see that the grease is free of abrasiveparticles (sand, dirt, lime, etc.), resins, and mineral salts. Table 2-2 gives thegreasing-interval recommendations of one pump manufacturer. Note that this is for avertical pump. Time intervals for greasing bearings in horizontal pumps will varysomewhat, depending on the type of bearing, pump service conditions, and otherfactors.

Fig.6. (a) Double type outboard bearing. (b) Water lubricated bearing for deepwell turbine pump(c) ball bearing with cooling jacket (d) Oil lubricated bearing for deepwell turbine pump.



Regreasing.

To replace the grease in a new or used antifriction bearing, remove thebearing from the shaft. Using a brush, wash the race, balls, and other parts withwarm kerosene or carbon tetrachloride. Soak the bearing in one of these solventsuntil the grease on it starts to dissolve. Use an innert-air hose to blow the grease offthe bearing parts.

Wash the bearing housing out with the same solvent. When both it and thebearing are clean, flusih both with clean mineral oil. Allow the oil to drain to waste.Check the cleanliness of the bearing by rotating it slowly. If it turns smoothly, youcan assume it is clean. Do not use kerosene or carbon tetrachloride at atemperature higher fhan 50 C when cleaning the housing and bearing.

Pump Exterior.

Clean all external surfaces of The pump and its driver. Use rags or waste to removedirt, dust, oil drippings, globs of grease, and similar matter. It is important to havethe pump spotless if accidents and other operating troubles are to be avoided.

Check the suction and discharge piping to see that flanges and screwedjoints are tightly made up and will not leak. Where automatic valve operators areused, check their operation by opening and closing the valves several times. To besure that the valve operating mechanism is working satisfactorily, use the manualcontrols to open and close the valves.

Auxiliary Piping.

Check the auxiliary piping and liquid supply by opening the cooling-watersupply and discharge valves (Fig. 9) and observing the liquid flow. Where anindependent oil pump is used, start it and check the pressure and flow in the variouslube-oil lines. Check the cooling-water and oil flow at the pump bearings. See thatthe stuffing-box jackets and smothering glands, if used, have a sufficient supply ofclear cool water.

Pump Drive.

Check the motor, turbine, engine, or other drive to see that it is lubricatedand ready to operate. Whenever possible, solo-run the drive independently of thepump to see that it is in good operating order. Follow the manufacturer’sinstructions for drive operation. Remember, the drive generally is not supplied bythe pump manufacturer. So directions for drive operation may, or may not, beincluded with the pump instruction manual.



Priming.

Prime the pump by one of the methods given by the manufacturer’srecomendation. Take care to see that the suction pipe is full of liquid and that thereis enough reserve in the supply system to keep the line full while the pump operates.Reduced flow into the suction pipe of a centrifugal pump can lead tooverheating and extensive damage to the pump.

Position the Valves.

Open the suction valve wide. Never use it as a throttling device for pumpflow. With a medium- or high-head centrifugal pump it is best to start with thedischarge gate valve closed. This is because the pump requires less power inputwhen primed and operated at full speed with the discharge valve closed.

Mixed-flow-type centrifugal pumps often require greater power input whenstarted with the discharge valve closed than when it is open. Axial-flow-typecentrifugal pumps almost always take more power when started with the dischargevalve closed. So it is common practice to start these two types with the dischargegate valve open. But to be certain, check with the pump manufacturer.

The Hydraulic Institute recommends that, except in the case of axial ormixed-flow pumps, units driven by squirrel-cage induction motors havingreduced-voltage starting control should always be started with the discharge gatevalve closed. With this type of motor using across-the-line starting, the dischargegate valve can be opened before the pump is started. But the length of time theelectrical disturbance caused by the starting cycle lasts may be reduced by keepingthe gate valve closed.

Standard Motors.

General-purpose synchronous motors of ratings up to 500 hp (372.8 Kw)at 80 per cent power factor, and those having speeds of 500 rpm or higher at unitypower factor, have sufficient pull-in torque to start centrifugal pumps with thedischarge gate valve closed. At higher ratings and speeds below 500 rpm, standardsynchronous motors do not have enough pull-in torque to start a pump when itsdischarge gate valve is open. Specially built motors can, however, be obtained tostart under these conditions. The remarks above on the starting methods forinduction motors also apply to synchronous motors.

Where a centrifugal pump must be started with the discharge gate valveopen and the starting current must be held to a minimum, use a wound-rotorinduction motor where alternating current is available. This type of motor developsfull-load torque without taking an excessive line current. A d-c motor can also be



used, if a suitable power supply is available. It will develop full-load torque withoutthe line current’s exceeding 125 to 200 per cent of the normal full-load current.

Pump Warmup.

With pumps handling hot water or other hot liquids, the casing, rotor, andother parts must be brought to within a temperature of 10 to 38 C of the liquidbefore the unit is started. This prevents unequal expansion, with the possibility ofcontact between the moving and stationary parts. Some long pumps actually bowor arch when the top half is hot while the bottom half is cold.

Open the vent valve on top of the casing and admit warm liquid to thepump. Use one or more casing drains to increase the liquid flow from the pump,thereby reducing the time required for warm-up. Boiler-feed pumps, and unitshandling valuable or toxic liquids, cannot economically be warmed up in thismanner. Instead, a jumper line around the discharge check valve is used. Hot liquidflows through this line, into the pump, and out the suction pipe. In a 4.542 Cubicmeter/minute feed pump, a warmup flow of 37.8 liter/minute is enough to bringthe pump temperature to within 38 C of the liquid handled.

Pumps having labyrinth leakoffs in the stuffing box generally do not need ajumper line. Drainage through the leakoff is usually of sufficient quantity to keep thepump warm, if the leakage is made up with hot liquid from the suction line. At liquidtemperatures of 175 C or higher, a period of 3 to 4 hrs. should be allowed forpump to warmup, when starting from a cold condition. Shorter intervals may beused when the pump is warm before heating is begun.

Starting the Pump.

The following steps are usually suitable for starting a centrifugal pump ingood operating condition:

(1) Turn on the cooling-water system for the pump bearings,stuffing boxes, and mechanical seals, if these parts areliquid-cooled. (2) Start the auxiliary lube-oil pump, if one is fitted, and check theoil flow to the bearings and other parts of the pump. (3) Open the suction gate valve, and close or open the dischargegate valve, depending on the starting procedure to be followed. (4) Close all the drains in the casing and suction and dischargepiping. (5) Prime the pump. (6) Open the warmup valve if the pump is not at the righttemperature. (7) Open the recirculating valve. (8) Start the driver and bring the pump up to speed.



(9) As soon as the pump is up to rated speed, open the dischargegate valve slowly. (10) Check the leakage from the stuffing boxes. (11) Adjust sealing-liquid flow to ensure packing lubrication. Aflow of 3 to 7 liter/min to each stuffing box is usually sufficient. (12) Check the pump bearings for lube-oil flow. (13) When there is sufficient flow through the pump, close therecirculating valve. (14) Check the pump suction, discharge, lube-oil, cooling-water,and sealing-water pressures and temperatures. Bearingtemperatures generally should not exceed 65 C during pumpoperation.

The above steps are suitable for almost all centrifugal pumps. Some stepsmay be omitted with smaller units not having separate cooling and oil systems. If thepump shows any signs of trouble while being started such as overheated bearings orpacking, excessive vibration or noise stop the unit immediately. Inspect the pumpfor the cause of the trouble and take corrective action before starting the pumpagain.

Fig. 10. (a) Internal seal used with clean liquid



Fig 10 (b) External seal for dirty liquids

Stuffing Boxes.

On pumps using discharge liquid for the stuffing boxes (Fig. 10a) close thesealing-liquid valves while the pump is being started on a suction lift. When liquid isbeing discharged by the pump, open the sealing valves. Adjust until there is a slightbut constant leakage of liquid from the stuffing-box glands. With an externalseal-liquid supply (Fig. 10b) turn on the control valve before starting the pump.Figures 10c and 10d show two other sealing arrangements.

Bypass Use.

The recirculation or bypass connections should be cut in whenever thepump must run at shutoff or at 20 per cent or less of its rated capacity. Be sure therecirculated or bypassed liquid flows to a lower-pressure area where it can releasesome of its heat before returning to the pump. Then, there will be no danger of thepump’s overheating. The bypassed liquid is often returned to the source of suctionsupply, but not directly to the pump suction.



Fig 10 (c) External grease seal for non-lubricating liquid, or where water cannot be used.

In boiler-feed pumps the maximum allowable temperature rise usuallyrecommended is 10 C. But when the pump handles cold water a higher rise 15 to38 C may be permitted. The exact rise allowable limits must be obtained from thepump manufacturer. A rule of thumb often used is: To limit the temperature rise ofthe water in a boiler-feed pump, do not reduce the capacity below 113 liters/minper 100 hp or 74.5 Kw input to the pump at shutoff. Many centrifugal boiler-feedpumps have an orifice in the bypass line. The orifice is sized to pass the minimumsafe-flow quantity for the pump.

Excessive throttling of the discharge gate valve can also lead to overheatingof a pump. When only a small percentage of the rated flow is allowed to passthrough the pump, the casing may be unable to radiate enough heat to keep thetemperature constant. This is because the excess horsepower put into the pump,over that delivered by the liquid, appears as heat in the liquid. Noisy operation,over-heating, and shaft breakage are some of the operating troubles that may result.



Fig. 10 (d) Seal cage next to impeller keeps abrasive liquid away from packing or mechanical seal.

Standby Pumps.

When keeping a standby pump hot by circulating hot liquid, use thefollowing operating methods:

(1) Circulate coolingwater through the bearings, packing boxes, and lantern rings. (2)Circulate oil to the bearings. (3) Start the pump once each 8-hr shift, bringing it up to full speedand operating it for 3 or 4 minutes if they are not in the RCMconvention.

When the pump is on hot-oil or other service where the liquid handled maycoke or plug the passages, start the pump twice each 8-hr shift. Standby boiler-feedpumps are generally held in readiness with the suction and discharge gate valvesopen at all times. Be sure to have sufficient liquid in the suction well, tank, or pondwhen keeping a pump on standby.



Fig. 11. Typical boiler-feed pump log

Fig. 12 Cooling jacket for stuffing box operating at 120 C, or higher

Operating Checks.

While the pump runs, make the hourly checks listed below: bearingtemperature, suction and discharge pressure, lube-oil temperature and pressure,leakoff flow, discharge flowmeter, stuffing-box leakage, cooling-water suction anddischarge temperature and pressure, input to the pump driver and the oil level in thepump and driver bearings. Keep an hourly record of all these readings, using a logsheet (Fig. 11) developed for the particular installation. When the pump is fittedwith water-quenched glands (Fig. 12) shut off the quenching-water supply before



frying to determine the leakage from the stuffing box. Otherwise, thequenching-gland flow may be mistaken for leakage from the stuffing box (Fig. 10).The condition of the packing box can often be checked by feeling the gland whilethe pump is running (Fig 13). When the pump handles cool liquids, the glandhandles cool liquids, the gland should not be too hot to touch. With hot liquids thistest cannot be used because heat is transmitted from the liquid pumped to thegland.

Fig. 13. Checking stuffing-box temperature by hand.

Check ring-oiled or ball sleeve bearings every hour to see that the oil rings(Figs. 3 and 4) are taming freely and supplying enough oil to the bearings andshaft. With any pump having oil-lubricated bearings it is wise to rotate the shaft afew times by hand before starting for the first time when the oil is cold and thebearing surfaces dry. This starts a flow of lube oil to the bearing surfaces, reducingthe possibility of overheating of the bearings during starting.

When making the hourly round of a pump, listen to the sound it makes whilerunning. Any change in the sound should be carefully checked because it may be thefirst sign of impending trouble. Increased vibration and sudden changes in thebearing temperatures are other indicators of possible operating troubles.

Steam-turbine-driven Pumps.

Warm the turbine before starting by opening the steam exhaust valve and alldrains on the steam inlet and exhaust, and the turbine casing. Rotate the shaft atleast once by hand to see that it is free. Heat the turbine casing by cracking thesteam-inlet throttle valve and allowing a small amount of steam to pass through tothe exhaust line. Allow steam to enter the casing until the unit reaches its operatingtemperature. Open all drain valves wide to remove all condensate from the casingand steam lines. When the lines and casing are dry, close all drains, open the throttlevalve, and quickly bring the turbine up to rated speed. The governor will then takeover control of the turbine speed. Prepare the pump driven by a turbine in the samemanner as described earlier for other centrifugal pumps.



Balancing-chamber Leakoff.

Be sure that the leakoff from the balancing chamber of a multistage pump isalways open while the unit runs. Shutting off flow from the chamber may prevent thedrum from functioning, severely damaging the pump. When the pump is used inboiler-feed service, connect the balancing-chamber leakoff to the nearestconvenient liquid tank on the suction side of the pump. Since this is at a lowerpressure than in the chamber, leakoff liquid will automatically flow while the pumpoperates. In general, do not connect the leakoff line to the pump suction nozzle orpipe.

Mechanical Seals.

These are now used instead of packing in every pumps. When applied tohigh-pressure high-temperature service, some seals have a quench connection.Others, known as double seals, are used where the liquid is corrosive or abrasive.This type generally has an auxiliary pump and reservoir. The small auxiliary pumpcirculates lube oil through the seals to lubricate and cool them. Start the auxiliarypump and establish oil circulation before the main pump is started. Pumps handlingclean cool liquids sometimes bypass a small portion of the discharge to themechanical seals to cool and lubricate them. Be certain to open any valves in theseand the quench connections before starting the main pump.

Casing Gasket.

Before starting split-casing pumps for the first time, tighten the casing bolts.If the manufacturer recommends using a torque wrench, do so. This will ensure thatsufficient pressure is obtained on the paper or asbestos flange gaskets. Aftertightening flange bolts, tighten the shaft-sleeve nuts on packed pumps. Then thesleeve will rotate properly with the shaft.

Couplings.

Some gear-type shaft couplings must be filled with oil or grease before thepump is started for the first time. Do not over-fill oil-type couplings because thepack-oil may leak out while the pump operates, damaging the pump room walls,ceilings, lights, or other fixtures. Figure 15 shows the three steps to be followed infilling grease-packed gear-type couplings.



Fig. 15. Steps in packing a gear-type coupling. (a) Pack grease over grid and teeth. (b) Draw up cover and fasten with bolts. (c)Lubricate at least once every 6 months, using a grease gun.

Starting Marine Pumps.

Centrifugal pumps in shipboard uses are usually motor- or turbine-driven.On some small vessels the pump may be belt-driven from an electric motor or anengine shaft. Use the same starting procedure given earlier, except that more thanone valve may have to be opened in the suction line when the pump is connected toa manifold. In general, the discharge gate valve can be left open, if desired, if thepump is driven by a d-c motor. For most other drives the discharge gate valveshould be left in the position described above.

Belt-driven pumps need not be aligned quite so accurately with the driveshaft as coupled pumps. This is because the belts can operate with somemisalignment of the shafts without excessive wear. But to obtain best life from thedrive belts, align the shafts and sheaves as accurately as possible. Then the belts willlast longer and will operate more quietly.



Fig.16. Chart for best operating scheme.

When to Start Second Pump.

In some services, like boiler-feed, condenser-circulating water, and others,there is a definite point at which it is economical to start a second pump to aid thefirst in delivering to the system they serve. With circulating-water pumps thiscondition usually occurs in the spring and fall of the year. Below a certain watertemperature, running the second circulating pump reduces the overall plant efficiencybecause the input to the pump motor exceeds the additional generator outputproduced by the better vacuum. But above this temperature, the reverse holds truethe extra output from the generator is greater than the input to the pump motor andthe plant efficiency is higher. Figure 16, when used with the heat-rate correctionchart furnished by the turbine manufacturer, helps show when to start or stop thesecond circulating pump, if the plant is fitted with two.

Example: A turbine-generator unit operating at 100,000 kw shows a net change of 0.3 per cent in the gross heat rate when its 600-hp second circulating pump is started. Should the pump be left running or be stopped?

Solution: Enter Fig. 16 at the left at a gross generation of 100,000 kw and draw a straight line through the change in gross heat rate, 0.3 per cent in this case. Prolong this line until it intersects reference scale K. From this point draw a straight line through the circulating-pump horsepower. Extend it to the right. Scale



Q shows the circulating pump should be stopped to secure the best net heat rate for this particular unit.

In actual operation, start or stop the second circulating pump, depending onwhether it is idle or running. Then note the change in the condenser back pressure(vacuum). Find the corresponding change in the unit heat rate from the turbinemanufacturer’s curve. Solve as described above.

Pump Shutdown.

When the liquid supply is above the pump centerline, close the dischargegate valve, then the suction gate valve. Shutoff the power immediately. When theliquid supply is below the pump (suction lift), close the suction gate valve, then thedischarge gate valve. Immediately after, shut off the power or steam to the driver.This procedure keeps liquid in the pump, preventing damage should the unit bestarted before being primed. If the pump has a recirculating line, close its valvebefore the pump stops. Open the warmup valve if the pump is to be kept warm.

When a pump operates against a high discharge pressure it should bestopped in three steps:

(1) Partially close the discharge valve. (2) Shut off the power. (3) As soon as the power is off, close the discharge valve rapidly.The discharge valve should be tightly closed by the time the pumpstops rotating.

Then there is no possibility of backflow causing the pump to turn in areverse direction This procedure also prevents water hammer in high-pressure lines.If the pump is not to be started, hang a suitable tag on it. Do not shut off the coolingand sealing liquid supply until the pump shaft has stopped turning. When the pumpcannot be run against a closed gate valve, stop the motor or turbine before closingthe discharge gate valve.

Remember, an idle pump will partially drain through the glands while notoperating. So be sure to prime it before starting again. Never run any centrifugalpump dry. Serious damage will almost always result. When the pump is on standbyservice, its suction and discharge gate valves should be left open. Do not tighten thegland nuts to prevent leakage from the pump unless they can be loosened quicklywhen the unit is started.



Flushing Plant Piping.

At PP(T)SB, it is mandatory to flush the piping with liquid discharged byone or more pumps (if used) . The end of the pipe is connected to the sewer orsome other disposal point and water or other liquid is pumped through. Thisprocess serves two purposes it is a convenient way of cleaning any refuse or othermatter from the new piping and it permits a good check of the performance of thepump.

When flushing the piping a good opportunity is afforded for checking thestuffing-box packing (if used). Check the packing box by feel as soon as the pumpstarts and regularly thereafter while the pump runs. If the box overheats or begins tosmoke, shut the pump down immediately. Allow the box to cool and start the pumpagain. Check its temperature as before (Fig.13). If it overheats, stop the pumpagain. It may be necessary to start and stop the pump several times before thepacking is ‘worn-in’ and some of the liquid pumped can leak through to lubricate it.If the box continues to overheat, inspect and repack it.

Pneumatic Pumps.

Air-driven sump pumps are popular in our industrial and construction jobs.Before putting a unit of this type into service:

(1) Blow out the air-supply hose to remove any water or dirt beforeit is attached to the pump. (2) Pour a small amount of clean ISO #10 oil into the live-air inlet.(3) Remove the oil plug and fill the lube-oil reservoir with the samegrade as in (2), above. (4) Check the air-exhaust pipe to see that its outlet is above thewater level and free of dirt and other obstructions. (5) Connect the air-supply hose. Maintain an air pressure of atleast 6.5 Kg/Cm2 at the pump. Some pumps use other pressures besure that the pressure at the pump air inlet is not more than 5 percent below the rated inlet pressure.

Mount the pump on a flat stone or board so that it is above any muck orsettlings in the sump. If the liquid being pumped is extremely dirty, place the pump ina wire basket or screened box. When the pump is taken out of service overnight,drain all water from it and disconnect the air-supply and exhaust hoses. Pour a smallamount of oil into the live-air inlet, connect the air hose, and allow the pump to idlefor about a minute. Disconnect the hose.



Spare Parts.

The number of spare parts which should be kept on hand varies with thepump application. Thus, aboard ship more parts are generally carried than in astationary plant. Most manufacturers recommend that the minimum number ofspares should be one set of shaft bearings, one set of shaft sleeves, one set ofwearing rings, and a supply of suitable set of packing or mechanical seals for thestuffing boxes. On vital jobs where a standby pump is not installed, stock acomplete spare rotating element.

When ordering spare parts, always remember to give the manufacturer thefollowing information: serial number of pump, size and type of pump as given on thepump name-plate, the exact number of the part as listed in the pump instruction andparts manual, and the name of the part, as listed. Where possible, give the completesymbols stamped on the old part. This is important information hence our pumps arenot purchased off-the shelve.

////////////////////////////////////////////////////\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\

References:

(1) Hydraulic Institute. (2) Ingersoll-Rand Co. (3) Peerless Pump Div. (4) Layne & Bowler, Inc. (5) Westinghouse ElectricCorp. (6) Allis-Chalmers Mfg. Co. (7) Power. (8) Worthington Corp. (9) Falk Coupling Div, Borg-Warner Corp. (10) EbaraCorporation. (11) Pacific-Hiro pump Div, Shin Nippon Machinery (12) EKK Eagle Industry Co. Ltd. (13) Lubrication SystemsCompany. (14) American Petroleum Institute. (15) Institution of Electrical and Electronic Engineers. (16) Institution ofDiagnostic Engineers.



centrifugal pump operation

Documents

pump bearings

pump rotation

pump shaft

pump alignment

pump manufacturer

pump inlet

pump footings

horizontal centrifugal