Pumps

WEL COME TO PERSONALITY DEVELOPMENT AND VOCATIONAL TRAINING

BY A.Antony Peter

PUMPS

A Pump is a machine , when driven from some external source like a motor or a diesel engine lifts water or liquid from lower level to higher level.

A Pump is a machine which converts Mechanical energy into Pressure energy.

PUMP Pump is a mechanical device to increase the pressure energy of a liquid. In most of the cases pump is used for raising fluids from a lower level to a higher level. This is achieved by creating a low pressure at the inlet or suction end and high pressure at the outlet or delivery end of the pump.Due to the low inlet pressure the fluid rises from a depth where it is available and the high outlet pressure forces it up to a height where it required

PUMPS A Pumping system consists of • Pump • Prime Mover • Suction Pipeline • Delivery Pipeline

Layout of a pumping system

Delivery head

Overhead tank

Delivery valve Delivery pipe

SH

Pump Strainer & foot valve

Suction pipe

CLASSIFICATION OF PUMPS PUMPS

Positive displacement pump

Reciprocating pump

Rotary pump

Rotodynamic pump

Centrifugal pump

Axial pump

Semi Axial pump

Positive Displacement What is meant by positive displacement pump? Positive displacement pump means that for changes in efficiency the pump out let is Constant regardless of pressure.The out let is positively sealed from the inlet,So that what ever gets in is forced out through out let port

CLASSIFICATION OF PUMPS

Reciprocating pump Piston pump

Plunger pump

Bucket pump

RECIPROCATING PUMP A reciprocating pump consists of a piston reciprocating inside a close fitting cylinder , thus performing the suction and delivery strokes. The reciprocating pump is a positive acting type which means it is a displacement pump which creates lift and pressure by displacing liquid with a moving piston. The cylinder is alternately filled and emptied by forcing and drawing the liquid by mechanical motion This type is also called ‘Positive displacement’ pump

HAND PUMP

Centrifugal pump

Single Stage pump

Multi Stage pump

i) CENTRIFUGAL PUMP The Pump which raises water or a liquid from lower level to Higher level by the action of centrifugal force is known as Centrifugal Pump.

This above idea of lifting water by centrifugal force was first given by L.D.Vinci,an Italian Scientist and Engineer.

Centrifugal Pump

+

Delivery pipe Impeller Pump casing

Suction Pipe

Foot valve

CENTRIFUGAL PUMP

Principle of operation of centrifugal pumps • The pump consists of an impeller which is mounted in a housing. The impeller is driven at 1775 to 3400 rpm within the housing. The water is drawn into the impeller and with the rapid rotation of the impeller. Pressure and velocity is created and water is thrown outwards with force.The impeller is the only moving part in the pump. The pump will not work against high heads. • Generally single stage pump is not used for heads exceeding about 300 feet.

Principle of operation of centrifugal pumps • The basic principle of operation on which a centrifugal pumps functions :the first step in operation of a pump is priming. Now the revolution of the pump impeller inside a casing full of water produces a forced vortex which is responsible for imparting a centrifugal head to the water. Rotation of impeller effects a reduction of pressure at the center. This causes the water in the suction pipe to rush into the eye. The speed of the pump should be high enough to produce centrifugal head sufficient to initiate discharge against the delivery head.

SUCTION PIPE. Suction pipe of a centrifugal pump plays an important role. A poorly designed suction pipe causes insufficient net positive Suction head, vibration, noise and excess wear. For this purpose bends in the suction pipe are avoided and its Diameter is often kept larger.

DELIVERY PIPE. PIPE A check valve is provided in the delivery pipe near the pump, In order to protect the pump from hammer and also to regulate The discharge from the pump . The size and length of the Delivery pipe depends up on the requirement.

Strainer and foot valve. • This is fitted at the end of the suction pipe and is submerged in water in such a way that it is only a few cm above the bottom of water to be pumped. The water from the sump or well first enters the strainer which is meant to keep the floating bodies away from the pump. In absence of strainer, the foreign material will pass through the pump and choke the pump. The cast foot valve is a non return or one way valve opening upward only. The water will pass through the foot valve and will not allow the water to move downwards.

Suction lift of a pump • The theoretical suction lift or suction head is equal to atmospheric pressure divided by the density of the fluid being pumped. In case of clean water ( cold ) it is 10.33 meters or 33.9 feet. Hence for other fluids maximum suction lift is 10.33 meters specific gravity of fluid

Priming of centrifugal pumps • The pressure developed by the impeller of centrifugal pump is proportional to the density of the fluid in the impeller. If the impeller is running in air , it will produce only a negligible pressure, which may not suck the water from its source. To avoid this , the pump is first primed . i.e. filled up with water.

Single stage pump. • It has one impeller keyed to the shaft. This is generally horizontal but can be vertical also. • It is usually a low lift pump.

Single stage pump.

Multi stage pump • It has two or more impellers keyed to a single shaft and enclosed in the same casing. Pressure is built up in steps. • The impellers are surrounded by guide vanes and water is led through a by - pass channel from the outlet of one stage to the entrance of the next stage until it is finally discharged into a wide chamber from where it is pushed on to the delivery pipe. • The pumps are used essentially for high working heads and the no of stages depends on the head required.

Volute casing • In this, the impeller is surrounded by a spiral casing. Such a casing provides a gradual increase in the area of flow, thus decreasing the velocity of water and correspondingly increasing the pressure. • But a considerable loss takes place due to formation of eddies in this type of casing.

Volute casing

Vortex casing • It is an improved type of volute casing, in which the spiral casing is combined with a circular chamber. In this casing , the eddies are reduced to a considerable extent and an increased efficiency is obtained.

Vortex casing

Volute casing with guide blades • In this type of casing , there are guide blades surrounding the impeller. These guide blades are arranged at such an angle, that the water enters without shock and forms a passage of increasing area, through which the water passes and reaches the delivery pipe. • The ring of the guide blades is called diffuser and is very efficient.

Volute casing

Closed impeller pumps • In this impeller , the vanes are covered with shrouds on both sides. This impeller is meant to handle non - viscous fluid such as ordinary water, hot water and chemicals etc. • For hot water cast steel impeller is recommended • Non ferrous impellers are used for chemicals which are liable to corrode a ferrous surface. • For pumping acids, the impellers and all inside surfaces in contact with the liquid should be coated with stone.

Semi open impeller pump • The impeller is provided with shroud on one side only. • This type of pump is used for viscous liquids such as sewage water, paper pulp, sugar molasses etc.

Open impeller pump • The impeller is not provided with any shroud. • Such pumps are used in dredgers and elsewhere for handling mixture of water , sand pebbles and clay. • The impellers has very rough duty to perform and is generally made of forged steel.

Check valve • These are usually known as non returning or foot valves. • These are designed to permit fluid flow in one direction only. • These valves are used in suction pipes mainly.

Check valve

Globe check valves • These valves are intended to prevent a reverse flow in the line after a pump has stopped. Or in the event of a leak. • These valve prevent dangerous back flow in a line when two or more fluids are being supplied to a common point at different pressures.

Globe check valves

Butterfly valves • These are low pressure valves of extremely simple design which are used to control or regulate flow. • The movement is simple and straight forward and is used only for 90 degree rotation of the full movement.

Butterfly valves

Ball valves • This valve is frequently used where it is desired to provide a free opening for thick liquids. • The valves are guided in cages and rest in a free open circular seat. • The balls are carefully ground and polished and properly balanced.

Ball valves

GATE VALVE

GATE VALVE

Effect of throttling the Valves • Reducing the pump capacity by throttling a gate valve in a suction line leads to cavitations, excessive noise and vibration

• Excessive throttling of a discharge gate valve leads to overheating of the pump since only a small percentage of the rated flow is pumped and the casing may be unable to radiate enough heat generated by the excessive power so that the temperature is constant.

Satisfactory operation of a stuffing box • A fundamental rule for satisfactory operation of a stuffing box is that there must be a controlled leakage, This is necessary because in operation , a stuffing box is a form of braking mechanism which generated heat. This friction is held to a minimum by the use of smooth polished surfaces and continuous supply of lubricant from the packings to the shaft/ packing interface. The function of stuffing box leakage is to assist in lubrication and to carry of the generated heat maintaining packing pressure at the lowest possible level helps to keep the heat generation to a minimum.

Centrifugal pumps should not be operated dry - why ? • In centrifugal pumps since there is a relative motion between the surfaces of the stationary and rotating wear rings, there must be a clearance between them.Some leakage must therefore occur during operation.This leakage is necessary to act as a lubricant and coolant to keep the surfaces separated and to prevent and seizing of the surfaces.For this reason , a pump should never be started unless it is filled with liquid.

Centrifugal pumps should not be operated keeping the discharge valve- why ? • If the discharge valve is closed, the flow of liquid can be stopped without building excessive pressure in the casing as the impeller ids free to rotate in the liquid resulting in generation of heat.

Radial flow pump. • Ordinarily all centrifugal pumps are manufactured with radial flow impellers

Mixed flow pump. • The mixed flow impeller is just a modification of radial flow type enabling it to pump a large quantity of water. Flow through the impeller is a combination of radial and axial flows and the impeller resembles the propeller of a ship. • Some mixed flow impellers look like a screw and are known as screw impellers.

Axial flow pumps • It is a roto dynamic pump, it is hardly justifiable to call it as a centrifugal pump because centrifugal force is not called into play for the generation of pressure.

Operation of reciprocating pump • During the suction stroke, the piston moves towards the right, thus creating vacuum in the cylinder. This vacuum causes the suction valve to open and the water enters the cylinder. During the delivery stroke, the piston moves towards left, thus increasing pressure in the cylinder . This increase in pressure causes the suction valve to close and delivery valve to open and the water is forced into the delivery pipe.

Parts of a Reciprocating Pump

Delivery Pipe Hd b Hs

d o R g n i t c Conne

o°

90° 180°

a Suction Pipe

Water Level

270° Rotating Crank

Parts of a Reciprocating Pump

Delivery Pipe Hd b Hs

d o R g n i t c Conne

o°

90° 180°

a Suction Pipe

Water Level

270° Rotating Crank

Parts of a Reciprocating Pump

Delivery Pipe Hd b Hs

90°

d o R g n i t c Conne

o°

180°

a Suction Pipe

Water Level

270° Rotating Crank

Parts of a Reciprocating Pump

Delivery Pipe Hd b Hs

90°

d o R g n i t c Conne

o°

180°

a Suction Pipe

Water Level

270° Rotating Crank

Parts of a Reciprocating Pump

Delivery Pipe Hd b Hs

90°

d o R g n i t c Conne

o°

180°

a Suction Pipe

Water Level

270° Rotating Crank

Parts of a Reciprocating Pump

Delivery Pipe Hd b Hs

90°

d o R g n i t c Conne

o°

180°

a Suction Pipe

Water Level

270° Rotating Crank

Parts of a Reciprocating Pump

Delivery Pipe Hd b Hs

90°

d o R g n i t c Conne

o°

180°

a Suction Pipe

Water Level

270° Rotating Crank

Parts of a Reciprocating Pump

Delivery Pipe Hd b Hs

90°

d o R g n i t c Conne

o°

180°

a Suction Pipe

Water Level

270° Rotating Crank

Parts of a Reciprocating Pump

Delivery Pipe Hd b Hs

90°

d o R g n i t c Conne

o°

180°

a Suction Pipe

Water Level

270° Rotating Crank

Parts of a Reciprocating Pump

Delivery Pipe Hd b Hs

90°

d o R g n i t c Conne

o°

180°

a Suction Pipe

Water Level

270° Rotating Crank

Parts of a Reciprocating Pump

Delivery Pipe Hd b Hs

d o R g n i t c Conne

o°

90° 180°

a Suction Pipe

Water Level

270° Rotating Crank

Parts of a Reciprocating Pump

Delivery Pipe Hd b Hs

90°

d o R g n i t c Conne

o°

180°

a Suction Pipe

Water Level

270° Rotating Crank

Parts of a Reciprocating Pump

Delivery Pipe Hd b Hs

90°

d o R g n i t c Conne

o°

180°

a Suction Pipe

Water Level

270° Rotating Crank

Parts of a Reciprocating Pump

Delivery Pipe Hd b Hs

90°

d o R g n i t c Conne

o°

180°

a Suction Pipe

Water Level

270° Rotating Crank

Parts of a Reciprocating Pump

Delivery Pipe Hd b Hs

90°

d o R g n i t c Conne

o°

180°

a Suction Pipe

Water Level

270° Rotating Crank

Parts of a Reciprocating Pump

Delivery Pipe Hd b Hs

90°

d o R g n i t c Conne

o°

180°

a Suction Pipe

Water Level

270° Rotating Crank

Parts of a Reciprocating Pump

Delivery Pipe Hd b Hs

90°

d o R g n i t c Conne

o°

180°

a Suction Pipe

Water Level

270° Rotating Crank

Parts of a Reciprocating Pump

Delivery Pipe Hd b Hs

90°

d o R g n i t c Conne

o°

180°

a Suction Pipe

Water Level

270° Rotating Crank

Parts of a Reciprocating Pump

Delivery Pipe Hd b Hs

90°

d o R g n i t c Conne

o°

180°

a Suction Pipe

Water Level

270° Rotating Crank

Parts of a Reciprocating Pump

Delivery Pipe Hd b Hs

90°

d o R g n i t c Conne

o°

180°

a Suction Pipe

Water Level

270° Rotating Crank

JET PUMP • It is used for lifting water from the deep wells.A jet pump in its simplest form consists of a pipe having a convergent end at its bottom. The upper end of the pipe leads to the required height.Water under a high pressure is introduced to nozzle. The pressure energy of the water is converted in to kinetic energy,as it passes through the nozzle.As a result of this,the pressure in the convergent portion of the pipe is considerably reduced and the water is sucked in to the pipe.The sucked water after coming in contact with the jet, is carried in to the delivery pipe.

Discharge

Throat Nozzle

Strainer

AIR LIFT PUMP • Air lift pump utilises the compressed air for raising water.Because the density of mixture of air in water is much lower than the pure water.If such a mixture is balanced against a water column, former will rise much higher than the later. • Air lift pump, in its simplest form consists of an open vertical pipe with its lower end submerged into the liquid to be raised.The upper end of the pipe leads to the required height.The compressed air is introduced at the bottom of the pipe through a nozzle. • Advantages: It is quite simple in design. • No moving parts. • The initial as well as maintenance cost is very less • Disadvantages: Efficiency of the pump is very low.

AIR LIFT PUMP AIR

WATER

Nozzle

WELL

VANE PUMP

DIAPHRAGM PUMP

Difference between centrifugal &reciprocating pumps CENTRIFUGAL PUMP Low initial cost Occupies less floor space Construction is simple Low maintenance cost Less wear and tear Can handle dirty water Can run at higher speeds Delivery is continuous Operation is quite and simple Needs priming No air vessel is required

RECIPROCATING PUMP Initial cost is much higher Occupies more floor space Complicated construction High maintenance cost More wear and tear Can not handle dirty water Can not run at higher speeds Delivery is pulsating Care is required in operation Does not need priming Air vessel is required

Selection of pumps • Nature of liquid to be pumped Fresh or salt water , acid or alkaline Cold or hot in condition Specific gravity of the liquid Viscous or non - viscous.

• Capacity Required capacity as well as minimum and maximum amount of liquid to be pumped

• Suction conditions Suction head - how much ? No of bends and elbows in the suction pipe.

Selection of pumps - contd • Discharge conditions Delivery head - how much ? Friction head ? Length and diameter of delivery pipe ? • Total head How much is total head ?

Selection of centrifugal pumps based on specific speed S.no Specific speed in rpm 1 10 to 30 2 30 to 50 3 50 to 80 4 80 to 160 5 160 to 500 6 Above 500

Type of centrifugal pump Slow speed pump, with radial flow at outlet Medium speed pump , with radial flow at outlet High speed pump , with radial flow at outlet High speed pump , with mixed flow at outlet High speed pump , with axial flow at outlet Very high speed pump.

Specific speed of a centrifugal pump • The specific speed of a centrifugal pump may be defined as the speed of an imaginary pump, identical with the given pump, which will discharge one liter of water , while it is being raised through a head of one meter. • This helps in selecting the type of centrifugal pump.

Specific speed of a centrifugal pump SPECIFIC SPEED NS = N x √Q (H)¾

N = Actual speed of the pump Q = Quantity flowing in m³/sec H = Delivery Head in m

CHECKING FOR PROPER PUMP ALIGNMENT • The coupling faces must be checked both angular and axially. • The angular alignment can be checked by using a feeler or taper gauges between the coupling faces. • The axial alignment can be checked by using straight edges and feeler gauges.

SEQUENCE OF OPERATION FOR PROPER PUMP ALIGNMENT • Grout the bed plate by checking its level on all sides by using wedges or steel blocks. • After 3 to 4 days when the grout is set, remove the wedges and mount the pump. • Tighten the bolts and check the level again either with the level or dial indicator. • In case , some distortion is noticed correct it by inserting shims and tighten the bolts firmly. • Check the level again.

COMPARISON OF MONOBLOCK AND COUPLED PUMPS

S.NO PARAMETERS COUPLED PUMPS ELECTRIC MONOBLOCK 1 Loss of power in transmission Upto 5 % depending upon alignment Nil 2 Possibilities of misalignment Too often Nil 3 Matching of pump and motor rating May not be correct Is correct 4 Danger of overloading / underloading Very high Nil 5 Maintenance Cumbersome Negligible

4Q

Discharge

3Q

2Q

Q

0

N

2N

3N

4N

Speed

Characteristic curve for Speed verses Discharge

5N

Characteristic curve for Speed Vs Head 4H

Head

3H 2H

H

0

N

2N Speed

3N

4N

5N

Characteristic curve for Speed Vs Power 4P

Power

3P 2P

P

0

N

2N Speed

3N

4N

5N

TIPS IN PUMPING SYSTEM • To run the pump at the specified duty point Deviation on the duty points result in part load / over load conditions. This will affect the efficiency of the pumps and motors thereby power consumption. • To check up for the mechanical freeness of the pump and correct clearance I. E. at Bearings , Lubricants Gland packing Alignment etc. Failure on the above will result in increased friction which will force the pump to consume more energy.

TIPS IN PUMPING SYSTEM • To check up regularly for proper functioning of valves, suction strainers pipelines and other accessories. Non compliance of the above will result in change of pressures which will shift the duty point thereby the power absorbed will vary. • To change the wear out components / parts like impellers, wear rings shaft protection sleeve and gland packing etc with genuine spares periodically. Failure of the above will increase the clearances, excessive leakage will start which will all finally reduce the efficiency of the pump.

TIPS IN PUMPING SYSTEM • To run the pump at the specified duty point Deviation on the duty points result in part load / over load conditions. This will affect the efficiency of the pumps and motors thereby power consumption. • To check up for the mechanical freeness of the pump and correct clearance I. E. at Bearings , Lubricants Gland packing Alignment etc. Failure on the above will result in increased friction which will force the pump to consume more energy.

ENERGY BALANCE OF A CENTRIFUGAL PUMP

8

35

22

15

20

Delivered energy

Piping

Pump

Motor

Throttling of valves

Symptom Pump & suction line not primed properly Excessive suction lift Air leak in suction line Foot valve not submerged Incorrect direction of rotation Gland leak Foot valve too small Foot valve partly clogged Speed too low Impeller is damaged Impeller out of balance Insufficient or excessive lubrication Bearings incorrectly fitted Stuffing box incorrectly packed Pump shaft or sleeve worn

TROUBLE SHOOTING CHART Nature of trouble Pump fails Pump delivers Excess leak Heavy noise Bearings to deliver low quantity in stuffing box or vibration heating up * * * *

*

* * * *

* * *

* * * * * *

* *

* * *

* *

THANK

YOU