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Pumps and Pumping Theory. Pump PUMPS POSTIVE DISPLACEMENT DYNAMIC Based on PUMPING ACTION Based on ORIENTATION VERTICAL HORIZONTAL ROTARYRECIPROCATING.

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Presentation on theme: "Pumps and Pumping Theory. Pump PUMPS POSTIVE DISPLACEMENT DYNAMIC Based on PUMPING ACTION Based on ORIENTATION VERTICAL HORIZONTAL ROTARYRECIPROCATING."— Presentation transcript:

1 Pumps and Pumping Theory

2 Pump

3 PUMPS POSTIVE DISPLACEMENT DYNAMIC Based on PUMPING ACTION Based on ORIENTATION VERTICAL HORIZONTAL ROTARYRECIPROCATING SINGLE STAGEMULTI STAGE DIAPHRAGMPISTON/PLUNGER CENTRIFUGALAXIAL SCREWGEAR Based on NO. OF STAGES Based on TYPE OF SHAFT SEALING GLAND PACKING MECHANICAL SEAL Based on PORTABILITY FIXED PORTABLE (Wilden, Oil Transfer etc.) Based on Location CARGO SPACEOTHER SPACESENGINE ROOM Based on Speed Variability Variable speed Fixed Speed Based on Prime mover Diesel Engine Hydraulic Motor Compressed Air Steam Turbine Steam Reciprocating Mechanism Electric Motor

4 Classification of Pumps Based on Drive, pumps may be -Electric Motor Driven -Steam Turbine Driven -Steam Reciprocating Mechanism Driven -Compressed Air Driven -Diesel Engine Driven -Hydraulic Motor Driven

5 Rotodynamic & Positive Displacement Pumps

6 Static & Dynamic Head

7 Pump Performance Characterstics

8 Slip

9 Centrifugal Pump Performance Curve

10 Frictional Losses in Centrifugal Pumps

11 Actual Performance Curve

12 Losses in Centrifugal Pump

13 Centrifugal pump characteristics at constant speed

14 Centrifugal pump characteristics The effects of throttling discharge valve on discharge pressure, efficiency, power and npsh can be seen. The throughput of a centrifugal pump alters with discharge head or back pressure. A slow rate of discharge by a centrifugal cargo pump can be, explained by increasing head due to a restricted or very long discharge pipe, high viscosity of the liquid, discharge to a storage tank sited at a high level or even a partly open valve on the discharge line. Depending on application, centrifugal pumps can be designed with relatively flat H/Q curves or if required the curve can be steep to give a relatively large shut-off head. We can see from the power curve, that minimum power is consumed by the pump when there is no flow and when the discharge head is at its highest. This equates to the discharge valve being closed. Because maximum pressure with the discharge closed is only moderately above working pressure, a relief valve is not necessary for a centrifugal pump. It will be noticed that the efficiency curve for the pump is convex which means that maximum efficiency occurs at a point somewhere between maximum and minimum discharge head and throughput conditions.

15 Losses in Positive Displacement Pump

16 Rotodynamic pumps (or dynamic pressure pumps) In this a tangential acceleration is imparted to the fluid. Depending upon supply head they may require a positive displacement pump as a priming device. In general they would be used for medium to high discharge rates, they usually are confined to low viscosity fluids and generate only low to moderate pressure differentials.

17 Kinetic Pumps (Roto-dynamic) Centrifugal Pumps Rotation of a centrifugal pump impeller causes the liquid it contains to move outwards from the centre to beyond the circumference of the impeller. The revolving liquid is impelled by centrifugal effect. It can only be projected into the casing around the periphery of the impeller if other liquid in the casing can be displaced. Displaced liquid in moving from the casing to the delivery pipe, causes flow in the discharge side of the system.

18 Centrifugal Pumps The liquid in the impeller and casing of a centrifugal pump is also essential to its operation. In moving out under the influence of the centrifugal effect, it drops the pressure at the centre, to which the suction or supply pipe delivers the liquid to be pumped. The moving liquid acts in the same way as a reciprocating pump piston on its suction stroke. Provided that a centrifugal pump is filled initially with liquid and that flow is maintained, the suction stroke action will continue. If such a pump contains no liquid initially, it is as though an essential part is missing.

19 Types of centrifugal pumps The volute pump is so called because of the shape of the casing. The object of the volute is gradually to reduce the velocity of the water after it leaves the impeller, and so convert part of its kinetic energy to pressure energy. For general purposes the volute pump is commonly used. In some pumps, diffusers are used. These consist of a ring of stationary guide vanes surrounding the impeller, the passage through the diffuser vanes is designed to change some of the velocity energy in the fluid to pressure energy. The design is used for high pressure as in multi-stage boiler feed pumps. The diffuser passages are able to convert a larger amount of the kinetic energy of the liquid as it leaves the impeller into pressure energy. A single stage diffuser pump is able to deliver to a much greater head than an ordinary volute pump. The regenerative pump is used where a relatively high pressure and small capacity are required.

20 Centrifugal pump characteristics at constant speed

21 Centrifugal pump characteristics The effects of throttling discharge valve on discharge pressure, efficiency, power and npsh can be seen. The throughput of a centrifugal pump alters with discharge head or back pressure. A slow rate of discharge by a centrifugal cargo pump can be, explained by increasing head due to a restricted or very long discharge pipe, high viscosity of the liquid, discharge to a storage tank sited at a high level or even a partly open valve on the discharge line. Depending on application, centrifugal pumps can be designed with relatively flat H/Q curves or if required the curve can be steep to give a relatively large shut-off head. We can see from the power curve, that minimum power is consumed by the pump when there is no flow and when the discharge head is at its highest. This equates to the discharge valve being closed. Because maximum pressure with the discharge closed is only moderately above working pressure, a relief valve is not necessary for a centrifugal pump. It will be noticed that the efficiency curve for the pump is convex which means that maximum efficiency occurs at a point somewhere between maximum and minimum discharge head and throughput conditions.

22 Variable speed centrifugal pump In the case of a variable speed pump: 1.Head varies as the square of the speed. 2.Capacity varies directly as the speed. 3.Power varies as the cube of the speed since it is a function of head and capacity.

23 Construction of Centrifugal pumps Double eye Single eye

24 In single stage pumps a single impeller rotates in a casing of spiral or volute form and in multistage pumps two or more impellers are fitted on the same shaft. Fluid enters the impeller axially through the eye then by centrifugal action continues radially and discharges around the entire circumference. In double inlet pumps fluid enters from two sides to the impeller eye as if there were two impellers back to back giving twice the discharge at a given head. In multi- stage pumps the fluid from one impeller is discharged via suitable passages to the eye of the next impeller so that the total head developed (or discharge pressure) is the product of the head per stage and the number of stages, such a pump is often used for high pressure discharge at moderate speed (e.g. turbo-feed).

25 The casing usually has the suction and discharge branches arranged at the back so impeller and spindle can be removed from the front without breaking pipe joints. The number of impeller vanes is not ‘fixed but usually there are six to ten. The volute casing is like a divergent nozzle which is wrapped around the impeller and serves two main functions (1) it enables velocity energy to be converted into pressure energy, the degree of conversion is governed mainly by the degree of divergence (2) it accommodates the gradual increase in quantity of fluid that builds at discharge from the circumference of the impeller.

26 For the velocity to be constant the volute is made so that cross sectional pipe area increases uniformly from cut water to throat. With an impeller having six vanes then the cross sectional area of volute at No. 1 vane will be 1/6th of throat area as one vane is pumping 1/6th of the water quantity, similarly 1/3rd at No. 2 and so on, taking vanes in turn from cut water to throat. A common fault for repair with these pumps is the increase of clearance due to wear at the wearing ring (or sealing ring) faces. This allows connection between suction and discharge so drastically reducing efficiency. During overhaul, the wear ring clearances are checked and if clearances are more than recommended values, than they are renewed.

27 VERTICAL, SINGLE INLET, CENTRIFUGAL PUMP Marine pumps are usually installed with the shaft vertical and the motor above the pump. This positions the pump as low as possible for the best NPSH, takes up the least horizontal space and leaves the electric motor safer from gland or other leakage

28 Shaft sealing In the smaller pumps the shaft gland seal is by water cooled ordinary stuffing box. Stuffing box type glands may be packed with soft packing. Great care must be taken on these packings as they are very prone to nip and score the shaft severely if not properly adjusted.

29 Mechanical seal This consists of a fixed clamp ring on the shaft driving another ring cup, with packing rings on to the shaft, through driving pins. Ring cup and rings are free to slide along the shaft under the action of axial springs from the clamp ring. The cup ring presses on to a fixed ball ring which in turn sits in a ball socket joint in the back plate which bolts to the pump casting.

30 Mechanical Seal

31 Centrifugal Pump – Theory and Characteristics Centrifugal pumps are generally used for movement of large volumes of liquid at low pressures. Higher pressures can be obtained with multistaging

32 Centrifugal Pump – Theory and Characteristics

33

34 Losses in Centrifugal Pump

35 Centrifugal Pump – Theory and Characteristics

36 Net Positive Suction Head (NPSH)

37 Net Positive Suction Head Available (NPSHA)

38 Net Positive Suction Head Required (NPSHR)

39 Cavitation

40 NPSHA in Reciprocating Pumps

41 Centrifugal Pumps - Cavitation

42 Cavitation

43 Centrifugal Pumps - Priming

44 Centrifugal Pump - Parts

45

46

47 Air handling methods

48 A separate pipe from the suction pipe of the main pump is taken to a rotary air pump which is directly driven by a friction clutch operated spindle as shown. The rotor revolves in a special variable shaped chamber which is supplied with fresh water from a separate water tank attached to the air pump casing. The discharge pressure of the pump places the air pump in or out of operation by hydraulic pressure clutching in/out the operating spindle of the air pump.

49 WATER RING AIR VACUUM PUMP PRINCIPLE As the impeller vanes pass the suction port air is drawn in and trapped between the water ring and the pump shaft. This ‘slug’ of air is carried around and delivered to the discharge port, hence this pump is a positive displacement type. Due to the casing shape the water is made to flow from and towards the rotor centre during each revolution. The water motion is utilised to act as suction and discharge for the air through appropriate sets of ports.

50 Axial Flow Pump

51 Characteristic curves for an axial flow pump

52 Axial Flow Pump When large capacity, wide variation of low lift head at constant speed, conditions have to be met the horizontal or vertically arranged axial pump is the most suitable. An axial flow pump is one in which a screw propeller is used to create an increase in pressure by causing an axial acceleration of liquid within its blades. The incidental rotation imparted to the liquid is converted into straight axial movement by suitably shaped outlet guide vanes.

53 Axial Flow Pump Axial flow pumps are sometimes classed with centrifugal pumps although centrifugal force plays no useful part in the pumping action. A comparison of discharge characteristics shows that H/Q and working efficiency characteristics for the two pumps are quite different. Starting from the point of normal duty, throttling of the discharge of an axial flow pump reduces the flow but also causes a rise in pressure and power. With the valve closed and zero discharge, the head can be about three times greater and absorbed power about doubled. The action of throttling to reduce throughput would overload the electric motor and cause operation of protective devices. If the discharge of the centrifugal pump is closed in as previously described, the pressure rises by a moderate amount and power demand actually drops.

54 Positive displacement pumps These are those where the volume of the pump chamber is alternately increased to draw the liquid in (suction) and then decreased by forcing the liquid out (delivery). This maybe done by a reciprocating motion of a piston or plunger within a cylinder or by a rotary motion of specially designed vanes, gears or rotors. They do not require a priming device, in fact they may be used as priming devices. Positive displacement pumps must be fitted with relief valve and pressure regulating valve to safeguard the system. In general they would be used for small to medium discharge rates, they can pump fluids of a wide range of viscosity and can develop-especially in the case of the reciprocating pump-high pressure differentials if required.

55 Lift Pump On high: The lift pump upstroke creates a vacuum; water rises to fill it. The aspiration height doesn't exceed nine metres. When attempting to raise water by use of a vacuum pump, the weight of the air is insufficient to raise the water higher than nine metres (or 27 feet).

56 Reciprocating Pumps These types of pump operate by using a reciprocating piston. The liquid enters a pumping chamber via an inlet valve and is pushed out via a outlet valve by the action of the piston or diaphragm. Reciprocating pumps are generally very efficient and are suitable for very high heads at low flows. This type of pump is self priming as it can draw liquid from a level below the suction flange even if the suction pipe is not evacuated. The pump delivers reliable discharge flows and is often used for metering duties delivering accurate quantities of fluid.

57 Reciprocating Pump – single & double acting The reciprocating pump is not tolerant to solid particles and delivers a highly pulsed flow. If a smooth flow is required then the discharge flow system has to include additional features such as accumulators to provide even flows. Reciprocating pumps designed for delivering high pressures must include methods for releasing excessive fluid pressures. The pumps should include for built in relief valves or relief valves should be included in the fluid circuit which cannot be isolated from the pump.

58 Rotary Displacement Pumps- external gear pump

59 Internal Gear Pump It uses two rotating gears which un-mesh at the suction side of the pump to create voids which allow atmospheric pressure to force fluid into the pump. The spaces between the gear teeth transport the fluid on either side of a crescent to the discharge side, and then the gears re-mesh to discharge the fluid.

60 Lobe-pump A lobe-pump like a gear pump and was the earlier type of mechanical pumps used for supercharging of main engine. Now you will find it being used as a sewage pump.

61 Vane Type Pump A Vane Type Pump operation is based on the principle of increasing the size of the cavity to form a vacuum, allowing the space to fill with the incoming liquid, and then forcing the fluid out of the pump under, pressure by diminishing the volume. The sliding vanes or blades fit into the slots in the rotor. Ahead of the slots and in the direction of rotation, grooves admit the liquid being pumped by the vanes, moving them outward with a force of locking pressure that varies directly with the pressure that the pump is operating against. The grooves also serve to break the vacuum on the admission side. The operating cycle and the action of centrifugal force and hydraulic pressure hold the vanes in contact with the casing.

62 Single-screw pump or mono pump They consist of only one driven metal rotor rotating within an elastomer lined (elastic) stator. Liquid enters the inlet and as the rotor turns within the flexible rubber stator forming tightly sealed cavities between the screw and the casing and progresses towards the discharge side of the pump which moves the liquid toward the outlet. A. This movement creates a partial vacuum which draws liquid into the pump. Pumping action starts the instant the ROTOR turns. Liquid acts as the lubricant between the pumping elements. This pump produces a constant discharge with negligible pulsation. This type can handle highly abrasive liquids and can also pump liquids containing fairly large solid particles.

63 Double-screw pump Two screws run either with intermeshing contact or the screws are driven in phase by timing gears and synchronized to run with positive clearance.

64 Triple-screw pump

65 Triple-screw pump has three screw on parallel axis. The central screw is power driven and drives two outer idler screws directly without external timing gears. The centre screw is driven mechanically, through a flexible coupling. The two outer screws are driven by the fluid pressure and act purely as seals. The screws work in a renewable cast iron sleeve mounted in a cast iron pump casing. Pedestal bearings at the base support the weight of the rotors and maintain their axial position When the screws rotate, their close relation to each other creates pockets in the helices. These pockets move axially and have the same effect as a piston moving constantly in one direction. The liquid being pumped enters the suction opening, flows through passages around the rotor housing, and through the screws from each end, in opposed streams, toward the center discharge. This eliminates unbalanced hydraulic thrust. These pumps work well at high pressure and with high viscosity fluids (up to 4000 centistokes).. The screw pump is used for pumping viscous fluids, usually lubricating, hydraulic, or fuel oil.

66 Hand Pump:(Semi Rotary Pump)

67 Diaphragm Pump (Wilden Pump)

68 An air valve directs pressurized air to one of the chambers, this pushes the diaphragm across the chamber and fluid on the other side of the diaphragm is forced out. The diaphragm in the opposite chamber is pulled towards the centre by the connecting rod. This creates suction of liquid in chamber, when the diaphragm plate reaches the centre of the pump it pushes across the Pilot Valve rod diverting a pulse of air to the Air Valve. This moves across and diverts air to the opposite side of the pump reversing the operation. It also opens the air chamber to the exhaust.

69 Eductor An eductor is a type of jet pump. Unlike other pumps, an Eductor pump has no moving parts. It uses the Venturi effect of a converging-diverging nozzle to convert the pressure energy of a motive fluid to velocity energy which creates a low pressure zone that draws in and entrains a suction fluid.Venturi effect converging-diverging nozzlepressurevelocity It is a device which effectively utilizes the pressure energy in a flowing fluid to evacuate, entrap/suck other fluid and discharge it to a point as needed in a system.

70 Principle of Eductor A simple eductor pump, as illustrated, consists of a supply line, a nozzle, a suction line, a suction chamber, a diffuser, and a discharge line. After passing through the throat of the injector, the mixed fluid expands and the velocity is reduced which results in recompressing the mixed fluids by converting velocity energy back into pressure energy. The motive fluid may be a liquid, steam or any other gas. The entrained suction fluid may be a gas, a liquid, a slurry, or a dust-laden gas stream

71 Applications of Eductors Creating vacuum in Fresh Water Generator Mixing Foam and water in Portable Foam applicator Pumping put Engine Room Bilges,, Steering Flat Bilges and other Bilges Creating vacuum for Steam Turbine System Stripping Cargo tanks in Oil Tankers Drawing water from wells by supplementing the centrifugal pump

72 Mixing Water and Chemicals with Eductor 1. incoming water stream is restricted by a nozzle. 2. while the speed of the outgoing water is decreased by the inverted funnel shape at the bottom of the venturi. 3. results in a vacuum in the middle, where the chemical is sucked into the water stream. 4. chemical flow regulated by interchangeable metering tips. 5. water and chemical are thoroughly mixed as they leave the outlet.

73 Rotary Piston Pumps 1.Radial Piston Pump 2.Swashplate Piston Pump 3.Wobble Plate Pump 4.Bent Axis Piston Pump

74 Radial Piston Pump Radial Piston pumps include a rotating cylinder containing equally spaced radial pistons arranged radial around the cylinder centre line. A springs pushes the pistons against the inner surface of an encircling stationary ring mounted eccentric to the cylinder.The pistons draw in fluid during half a revolution and drive fluid out during the other half. The greater the ring eccentricity the longer the pistons stroke and the more fluid they transfer.

75 Swashplate pump Swashplate pumps have a rotating cylinder containing parallel pistons arranged radially around the cylinder centre line. A spring pushes the pistons against a stationary swash plate located at one end of the cylinder, which sits at an angle to the cylinder. The pistons draw in fluid during half a revolution and drive fluid out during the other half. The greater the swashplate angle relative to the cylinder centre line the further the longer the pistons stroke and the more fluid they transfer.

76 Wobble Plate Pumps This pump includes a stationary piston block containing a number parallel pistons arranged radially around the block centre(at least five). The end of each piston is forced against a rotating wobble plate by springs. The wobble plate is shaped with varying thickness around its centre line and thus as it rotates it causes the pistons to reciprocate at a fixed stroke. The pistons draw in fluid from the cavity during half a revolution and drive fluid out at the rear of the pump during the other half. The fluid flow is controlled using non-return valves for each piston.

77 Bent Axis Pump Bent axis piston pumps have a rotating cylinder containing parallel pistons arranged radially around the cylinder centre line. The cylinder is driven by an shaft which is arranged at an angle to the cylinder axis. the shaft includes a flange with a mechanical connection to each piston. As the shaft rotates the pistons are made to reciprocate over a stroke based on the relative angle of the shaft and cylinder.

78 Running Centrifugal Pumps in Series and in Parallel Case 1. Suppose you are asked to discharge at a faster rate (with more Q m3/hr) than possible with a single pump, what do you do? Case 2. Suppose you find that during discharging, that the shore tank is not receiving the specified amount of cargo due to increased back pressure, what do you do?

79 Running Centrifugal Pumps in Series and in Parallel A centrifugal pump will pump fluid at the point where the system curve intersects the pump curve. If you need more flexibility you can install another pump and operate it in either series or parallel with the first pump. For pumps in series - add heads, for pumps in parallel - add flowrates

80 Running Centrifugal Pumps in Series Centrifugal pumps are connected in series if the discharge of one pump is connected to the suction side of a second pump. Two similar pumps, in series, operate in the same manner as a two-stage centrifugal pump. Each of the pumps is putting energy into the pumping fluid, so the resultant head is the sum of the individual heads. There is no change in the quantity discharged

81 Running Centrifugal Pumps in Series When two (or more) pumps are arranged in series, their resulting pump performance curve is obtained by adding their heads at same flow rate as indicated in the figure below.pump performance curveheads If one of the pumps in series stops, the operation point moves along the system resistance curve from point 3 to point 1 - the head and flow rate are decreased.

82 Running Centrifugal Pumps in Series Centrifugal pumps in series are used to overcome larger system head loss than one pump can handle alone. For two identical pumps in series, the head will be twice the head of a single pump at the same flow rate. With constant flowrate the combined head moves from 1 to 2. In practice the combined head and flow rated moved along the system curve to 3. The first pump acts like a booster pump

83 Series Operation of Centrifugal Pumps Both pumps must have the same width impeller or the difference in capacities (GPM or Cubic meters/hour.) could cause a cavitation problem if the first pump cannot supply enough liquid to the second pump. Both pumps must run at the same speed (same reason). Be sure the casing of the second pump is strong enough to resist the higher pressure. Higher strength material, ribbing, or extra bolting may be required. The stuffing box of the second pump will see the discharge pressure of the first pump. You may need a high-pressure mechanical seal. Be sure both pumps are filled with liquid during start-up and operation. Start the second pump after the first pump is running.

84 Running Centrifugal Pumps in Parallel Pumps are operated in parallel when two or more pumps are connected to a common discharge line, and share the same suction conditions. When two or more pumps are arranged in parallel their resulting performance curve is obtained by adding their flowrates at the same head as indicated in the figure. performance curve head

85 Running Centrifugal Pumps in Parallel Centrifugal pumps in parallel are used to overcome larger volume flows than one pump can handle alone. For two identical pumps in parallel the flowrate will double (moving from 1 to 2) compared to a single pump if head is kept constant. In practice the combined head and volume flow moves along the system curve as indicated from 1 to 3. If one of the pumps in parallel or series stops, the operation point moves along the system resistance curve from point 3 to point 1 - the head and flow rate are decreased.

86 Parallel Running of Centrifugal Pumps Both pumps must produce the same head this usually means they must be running at the same speed, with the same diameter impeller. Two pumps in parallel will deliver less than twice the flow rate of a single pump in the system because of the increased friction in the piping. The shape of the system curve determines the actual increase in capacity. If there is additional friction in the system from throttling (see dotted line in the following diagram), two pumps in parallel may deliver only slightly more than a single pump operating by its self.

87 Parallel Running of Centrifugal Pumps If you run a single pump only, it will operate at a higher flow rate (A) than if it were working in parallel with another pump (B) because it will be operating further out on the curve requiring increased power. The rule is that if a pump is selected to run in parallel, be sure it has a driver rated for single operation. Parallel pumps are notorious for operating at different flows. Often a weaker pump is operating close to its shut off point while a stronger pump is operating to the far right of its curve and running out of NPSHA.

88 Operating Procedures for Positive displacement pumps Starting: Precaution: Never start a displacement pump without ensuring that all valves on the discharge line are open. Attempt to turn the pump shaft to ensure it is not seized. Ensure that the cocks to the pressure gauges are in line for indicating the pressure and not open to the atmosphere. Open appropriate valves on the discharge side where the liquid has to go. Open appropriate valves on the suction side. On fuel or lube oil transfer pumps you will find a manually controlled valve (bypass) to regulate pressure, release the spring load to start the pump at low load.

89 Starting Procedure for Positive displacement pumps contd. Start the pump and observe for any abnormal sounds, load on the motor, or pressure build up. (stop the pump immediately in case of any abnormality) If the liquid being drawn is from a distant tank below the level of the pump, the pump will take some time to draw the liquid. There will be a change in the running sound when the liquid reaches the pump. If the liquid is cold the pump is likely to make more noise. Observe pressure as the pump picks up liquid. Adjust pressure regulating valve to increase the discharge pressure to normal. Observe leakages at pump lands, valves, and along the pipe line. Incase the pump is having difficulty in drawing the liquid. Stop the pump and check suction filter. Clean if necessary. Heat up the liquid if the temperature is low.

90 Operating Procedures for Positive displacement pumps Stopping the pump: Stop the motor. Shut all valves on the suction and discharge side. Open bypass valve. Clean the suction filter if the pump has drawn oil from dirty tank or the last part of oil tank. Record operating times, pressures, soundings as per standing instructions on board.

91 Operating procedures for a Centrifugal pump Starting: Open the suction valve completely. Keep the discharge valve closed at this stage, Open the air vent and if the water comes out from it, close it (pump is now said to have been primed). If the pump is of the self-priming type with an attached vacuum pump, keep the air vent closed and open the check valve on the vacuum pump line. Start the motor (pump) When the discharge pressure has risen, open the discharge valve gradually. (For a self-priming arrangement, close the check valve connecting to the vacuum pump.) Changeover suction and discharge as required gradually. Monitor suction and discharge pressures, load on the motor, vibrations, and leakages through valves and glands. If necessary ‘nip up’ the glands.

92 Note 1: Starting the pump with closed discharge valve reduces the starting current on the motor and prevents damage to the pump parts. Since centrifugal pump is not a positive displacement type, there is no danger of build up of excessive pressure. Pup casing and parts have been design to withstand maximum pressure the pump can produce in this case. Note 2: In case the pump looses suction, prime it as soon as possible. Avoid running the pump without liquid even for short periods to minimise wear between the impeller and its guide ring (wearing ring). Operating procedures for a Centrifugal pump contd.

93 Stopping the pump: Incase of a pumps used for bilge or ballast line, before stopping the pump, you must run the pump ‘sea to sea’ for some time to flush the pump and the pipe line of contaminated water. Close the discharge valve Stop the motor Close Suction valves all other valves that were opened for use. Note:Record starting and stopping times as per ship board instructions & practices. Operating procedures for a Centrifugal pump contd.


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