Centrifugal & reciprocating pumps

intro & explaination

1. Presentation On Centrifugal & reciprocating pumps Applied Thermal & Hydraulic Engineering Submitted by : Chauhan Karan(130120109004)/Electrical Engg./B-1 Chippa Abdul ( 130120109005) / Electrical Engg. / B-1 Submitted To: ( 2140907) GANDHINAGAR INSTITUTE OF TECHNOLOGY

2. Pump Basics

3. WHAT IS THE PUMP ? A hydrodynamic pump machine is a device for converting the energy held by mechanical energy into hydraulic energy of a fluid Pumps enable a liquid to: 1. Flow from a region or low pressure to one of high pressure. 2. Flow from a low level to a higher level. 3. Flow at a faster rate. 1

4. There are two main categories of pump: Rotodynamic pumps. Positive displacement pumps. Diaphragm Piston Plunger Reciprocating Rotary Mixed flow Gear Lobe Sliding Vane Screw Axial flow Centrifugal Rotodynamic Turbine Positive displacement PUMP 2

5. Difference between centrifugal pump & inward flow hydraulic Centrifugal pumps are similar to inward flow reaction turbine but it is reverse in action. In case water turbine the water flows outer periphery radially inwards while the water in centrifugal pump flow radially outwards towrds the periphery. In turbine the flow from higher pressure to lower pressure & produces mechanical power at the shaft. While in pump the water flows from lower pressure towards higher pressure side on the expense of mechanical energy. In turbine the flow is accelerated due to centrifugal action while the flow is deaccelerated in pumps.

6. Applications of centrifugal pump To pump water from source to fields for agricultural and irrigation purposes. In petroleum installations to pump oil. In steam and diesel power plants to circulate feed water & cooling water respectively. Hydraulic control systems. Transfer of raw materials. Pumping of water in buildings. Fire fighting.

7. Pump Terminology

8. 1- Casing:- II. Circular casings for low head and high capacity. A volute is a curved funnel increasing in area to the discharge port. Volute Suction Impeller Construction of Centrifugal Pumps Casing generally are two types: I. Volute casings for a higher head. have stationary diffusion vanes surrounding the impeller periphery that convert velocity energy to pressure energy. 6

9. Radial flow Axial flow Mixed flow 2-Impeller Three main categories of centrifugal pumps exist 7

10. Heads of Pump: where : V s = Velocity of fluid in the suction pipe. V d = Velocity of fluid in the delivery pipe. h s = Suction head. h d = Delivery head. h fs = head losses in the suction pipe. h fd = head losses in the delivery pipe. 10 Static head ( H st ) H st = h s + h d

11. Manometric head ( H m ) : but and   where h f = h fs + h fd (where H L = impeller losses) Total head ( H ) (where ) When V s = V d Hence H m = H 11

12. Losses in pumps hydraulic losses :(i)losses in pump:(a)loss of head due to friction in impeller. (b)Loss of head due to shock & eddy’s from inlet to exit of impeller. (c)Loss of head in guide vanes due to diffusion and in casing. (ii)Other hydraulic losses:(a)friction loss in suction & delivery pipes. (b)Loss of head in heads, fittings, valves etc. 2)Mechanical losses 3)Leakage losses

13. Pump Efficiencies 1- Hydraulic Efficiency ( ζ h ) The normal value varies between 60% - 90% 2- Manometric Efficiency( ζ m ) 3 -Volumetric Efficiency ( ζ v ) The normal value lies between 97% to 98% 14

14. 4- Mechanical Efficiency ( ζ ) It is due to losses in the shaft, coupling, and other operation losses as vibration The normal value is 95% - 98% 5 - Overall Efficiency ( ζ o ) The normal value is 71% - 86% Discharge of a Centrifugal Pump 15

15. Pump Performance The performance of a pump is show by its characteristic curve, where the flow capacity (Q) is plotted against the delivery pressure or developed head (H). Head is measured in metres.

16. Centrifugal Pump Performance Curve A centrifugal pump uses the conservation of energy principle .It changes velocity energy into pressure energy . As the differential head (H) increases ,the flow rate (Q)decreases .The performance curve looks like this .

17. Centrifugal Pump Performance Curve A centrifugal pump uses the conservation of energy principle .It changes velocity energy into pressure energy . As the differential head (H) increases ,the flow rate (Q)decreases .The performance curve looks like this .

18. Losses due to Friction A centrifugal pump incurs head losses due to friction. The friction is caused by the fluid changing direction when travelling through the pump and by clearances within the pump .These losses vary with both head and flow.

19. Actual performance curve Subtracting the losses from the ideal gives the actual performance curve for the pump. Ideal Head –Losses =Actual Head It is possible to determine the useful power of a pump by the formula

20. Multistage centrifugal pumps The centrifugal pumps with two or more number of identical impellers are called multistage centrifugal pumps. The impellers of these pumps may be attached on the same or on different shafts. the multistage pumps are needed either to increase the head or the discharge compared to a single stage pump, accordingly the impellers are connected in series or parallel .

21. Two Impellers in Series Twice the pressure Same amount of water Direction of Flow

22. Priming of a centrifugal pump Methods of priming: 1. priming by hand 2. connection with city water mains 3.by providing priming pumps 4.self priming devices

23. Reciprocating pump Pumps are used to increase the energy level of water by virtue of which it can be raised to a higher level. Reciprocating pumps are positive displacement pump, i.e. initially, a small quantity of liquid is taken into a chamber and is physically displaced and forced out with pressure by a moving mechanical elements. The use of reciprocating pumps is being limited these days and being replaced by centrifugal pumps.

24. Reciprocating pump For industrial purposes, they have become obsolete due to their high initial and maintenance costs as compared to centrifugal pumps. Small hand operated pumps are still in use that include well pumps, etc. These are also useful where high heads are required with small discharge, as oil drilling operations.

25. Main components A reciprocation pumps consists of a plunger or a piston that moves forward and backward inside a cylinder with the help of a connecting rod and a crank. The crank is rotated by an external source of power. The cylinder is connected to the sump by a suction pipe and to the delivery tank by a delivery pipe. At the cylinder ends of these pipes, non-return valves are provided. A non-return valve allows the liquid to pass in only one direction. Through suction valve, liquid can only be admitted into the cylinder and through the delivery valve, liquid can only be discharged into the delivery pipe.

26. Main components

27. Working of Reciprocating Pump When the piston moves from the left to the right, a suction pressure is produced in the cylinder. If the pump is started for the first time or after a long period, air from the suction pipe is sucked during the suction stroke, while the delivery valve is closed. Liquid rises into the suction pipe by a small height due to atmospheric pressure on the sump liquid. During the delivery stroke, air in the cylinder is pushed out into the delivery pipe by the thrust of the piston, while the suction valve is closed. When all the air from the suction pipe has been exhausted, the liquid from the sump is able to rise and enter the cylinder.

28. Working of Reciprocating Pump During the delivery stroke it is displaced into the delivery pipe. Thus the liquid is delivered into the delivery tank intermittently, i.e. during the delivery stroke only.

29. Classification of Reciprocating pumps Following are the main types of reciprocating pumps: According to use of piston sides Single acting Reciprocating Pump: If there is only one suction and one delivery pipe and the liquid is filled only on one side of the piston, it is called a single-acting reciprocating pump. Double acting Reciprocating Pump: A double-acting reciprocating pump has two suction and two delivery pipes, Liquid is receiving on both sides of the piston in the cylinder and is delivered into the respective delivery pipes.

30. Classification of Reciprocating pumps

31. Classification of Reciprocating pumps According to number of cylinder Reciprocating pumps having more than one cylinder are called multi-cylinder reciprocating pumps. Single cylinder pump A single-cylinder pump can be either single or double acting Double cylinder pump (or two throw pump) A double cylinder or two throw pump consist of two cylinders connected to the same shaft.

32. Classification of Reciprocating pumps According to number of cylinder

33. Discharge through a Reciprocating Pump Let A = cross sectional area of cylinder r = crank radius N = rpm of the crank L = stroke length (2r) Discharge through pump per second= Area x stroke length x rpm/60 This will be the discharge when the pump is single acting.

34. Discharge through a Reciprocating Pump

35. Discharge through a Reciprocating Pump Discharge in case of double acting pump Discharge/Second = Where, A p = Area of cross-section of piston rod However, if area of the piston rod is neglected Discharge/Second =

36. Discharge through a Reciprocating Pump Thus discharge of a double-acting reciprocating pump is twice than that of a single-acting pump. Owing to leakage losses and time delay in closing the valves, actual discharge Q a usually lesser than the theoretical discharge Q th .

37. Slip Slip of a reciprocating pump is defined as the difference between the theoretical and the actual discharge. i.e. Slip = Theoretical discharge - Actual discharge = Q th . - Q a Slip can also be expressed in terms of %age and given by

38. Slip Slip Where C d is known as co-efficient of discharge and is defined as the ratio of the actual discharge to the theoretical discharge. C d = Q a / Q th . Value of C d when expressed in percentage is known as volumetric efficiency of the pump. Its value ranges between 95---98 %. Percentage slip is of the order of 2% for pumps in good conditions.

39. Negative slip It is not always that the actual discharge is lesser than the theoretical discharge. In case of a reciprocating pump with long suction pipe, short delivery pipe and running at high speed, inertia force in the suction pipe becomes large as compared to the pressure force on the outside of delivery valve. This opens the delivery valve even before the piston has completed its suction stroke. Thus some of the water is pushed into the delivery pipe before the delivery stroke is actually commenced. This way the actual discharge becomes more than the theoretical discharge. Thus co-efficient of discharge increases from one and the slip becomes negative.

40. Comparison of Centrifugal and Reciprocating Pumps Centrifugal Pumps Reciprocating Pumps 1. Steady and even flow 1 . Intermittent and pulsating flow 2 . For large discharge, small heads 2 . For small discharge, high heads. 3 . Can be used for viscous fluids e.g. oils, muddy water. 3 . Can handle pure water or less viscous liquids only otherwise valves give frequent trouble. 4 . Low initial cost 4 . High initial cost. 5 . Can run at high speed. Can be coupled directly to electric motor. 5 . Low speed. Belt drive necessary. 6 . Low maintenance cost. Periodic check up sufficient. 6 . High maintenance cost. Frequent replacement of parts. 7 . Compact less floors required. 7 . Needs 6-7 times area than for centrifugal pumps. 8. Low head pumps have high efficiency 8 . Efficiency of low head pumps as low as 40 per cent due to the energy losses. 9. Uniform torque 9 . Torque not uniform. 10 . Simple constructions. Less number of spare parts needed 10 . Complicated construction. More number of spare parts needed.