Lecture 4

Fluid Mechanics II

Muhammad Usman

Pumps ClassificationsPumps

Positive Displacment Pumps

Dynamic Pumps

Reciprocating Rotary Pumps Diapharm Pumps

Single Acting

Doubel Acting

Gear Pump

Lobe Pump

Screw Type

Centrifugal Pumps

Axial Flow

Radia Flow

Mixed Flow

Vane Type Pump

Centrifugal Pumps

Parts of the centrifugal Pump

• Pump casing (Vent to remove gases)• Pump shaft• Volute• Diffuser• Impeller• Stuffing box• Lantern Ring• Impeller wearing ring• Pump casing wearing ring

Two Types of Volute casings

Diffusers

Types Of impellersOpen, Semi open and closed.

Radial Flow Centrifugal Pumps

Axial Flow Centrifugal Pumps

Mixed Flow Centrifugal Pumps

Multi-Stage Centrifugal Pump

Wearing Rings

• Wearing rings are replaceable rings that are attached to the impeller and/or the pump casing to allow a small running clearance between the impeller and the pump casing without causing wear of the actual impeller or pump casing material.

Parts of Centrifugal Pump

Stuffing Box

• The stuffing box is a cylindrical space in the pump casing surrounding the shaft. Rings of packing material are placed in this space. Packing is material in the form of rings or strands that is placed in the stuffing box to form a seal to control the rate of leakage along the shaft.

Lantern Ring

• A lantern ring is a perforated hollow ring located near the center of the packing box that receives relatively cool, clean liquid from either the discharge of the pump or from an external source and distributes the liquied uniformly aroung the shaft to provide lubrication and cooling.

Mechanical Seals

• These have two basic parts, a rotating element attached to pump shaft and stationery element attached pump casing.

Cavitation

• The process of formation and subsequent collapse of vapor bubbles in a pump is called cavitation.

• It degrades the performance of the pump and it can also cause extensive vibration which could damage the pump bearing, wearing rings and seals.

Net Positive Suction Head

• The net positive suction head available (NPSHA) is the difference between the pressure at the suction of the pump and the saturation pressure for the liquid being pumped.

Preventing Cavitation

• Increasing the suction pressure by increasing the level of liquid in the tank.

• By decreasing the temperature of the liquid.

• By decreasing the head losses increasing the pipe diameter, reducing number of elbows, valves and decreasing the length of the pipe.

• By using additional prallel pumps.

Centrifugal Pump Characteristic Curve

Priming of the Centrifugal Pump

• The filling of pump casing before the start up is called priming of the pump.

Reciprocating Pumps

• Suitable for less discharge and higher heads.

• A positive displacement pump is one in which a definite volume of liquid is delivered for each cycle of pump operation.

Air Vessels

• An air vessel is a cast iron closed chamber having an opening at its base through which the water flows into the vessel or from the vessel.

• The purpose of using the air vessel to obtain unifrom discharge from the reciprocating pump.

Rotary Pumps

• Self primed due to their capacity to remove air from the suciton line.

• These pumps are used for systems require high suction lift.

• These are positive displacement and have constant discharge.

Gear Pump

Lobe Pump

Screw Pump

Vane Type Pump

Diaphragm Pump