Centrifugal pumps

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2. CENTRIFUGAL PUMPSQ.Give a number of examples for reducing of axial pressure/force in thecentrifugal pumps.A.There are three types of axial pressure (force balancing): a) The sealing device 2and1, equalizing hole 3 connects suction and dischargespace. b) Balanced impeller (used in multistage pumps). c) Simple balancing disk 1 and chamber 5. d)Q.What is the purpose of the shafts PROTECTING SLEEVE?A.Pump shafts are usually protected fromerosion, corrosion, and wear at the seal chambers, leakage joints,internal bearings, and in the waterways by renewable sleeves. Unlessotherwise specified, a shaft sleeve of wear, corrosion, and erosion-resistant material shall be provided to protect the shaft. The sleeveshall be sealed at one end. The shaft sleeve assembly shall extendbeyond the outer face of the seal gland plate. (Leakage between theshaft and the sleeve should not be confused with leakage through themechanical seal). Q.What is the function of a WEAR RING?A. The function of the wear ring is: Wear ring provides an easily andeconomically renewableleakage joint between the impeller and the casing.For efficient operation it is important to ensure that leakage from the highto low-pressure side is kept to a minimum. This is achieved by the use of 2 3. wearing rings. Traditionally these are fitted to the casing, to increase thelongevity of the impeller wear ring tires may be fitted.If the clearance becomes too large the pump efficiency will be lowered causing heatand vibration problems. Most manufacturers require that you disassemble the pump tocheck the wear ring clearance and replace the rings when this clearance doubles. Q. What is the function of a DIFUSER? A. The function of a DIFUSER is included in the casing of pump.Circular casing have stationary diffusion vanes surrounding the impellerperiphery that convert velocity energy to pressure energy. Conventionally, thediffusers are applied to multi-stage pumps.The casings can be designed either as solid casings or split casings.Solid casing implies a design in which the entire casing including thedischarge nozzle is all contained in one casting or fabricated piece. A split casing implies two or more parts are fastened together. When thecasing parts are divided by horizontal plane, the casing is described ashorizontally split or axially split casing. When the split is in a verticalplane perpendicular to the rotation axis, the casing is described asVertically split or radically split casing. Casing Wear rings act as the sealbetween the casing and the impeller.Q.What are the parameters that are responsible for the capacity and pressure in acentrifugal pump?A. CapacityCapacity means the flow rate with which liquid is moved or pushed by the pumpto the desired point in the process. It is commonly measured in either gallons perminute (GPM) or cubic meters per hour (m 3 /hr). The capacity usually changes withthe changes in operation of the process. For example, a boiler feed pump is anapplication that needs a constant pressure with varying capacities to meet achanging steam demand.The capacity depends on a number of factors like:Process liquid characteristics i.e. density, viscositySize of the pump and its inlet and outlet sectionsImpeller size3 4. Impeller rotational speed RPMSize and shape of cavities between the vanesPump suction and discharge temperature and pressure conditionsFor a pump with a particular impeller running at a certain speed in a liquid, theonly items on the list above that can change the amount flowing through the pumpare the pressures at the pump inlet and outlet. The effect on the flow through apump by changing the outlet pressures is graphed on a pump curve.As liquids are essentially incompressible, the capacity is directly related with thevelocity of flow in the suction pipe.D B RPM Q.Why are centrifugal pumps not provided with safety valve? A. A centrifugal pump does note create pressure, it only provides flow.Pressure is just an indication of the amount of resistance to flow.Q.How can we regulate the PRESSURE and CAPASITY of aCentrifugal pump? A. There are a few methods to change pressure and capacity ofCentrifugal pump:a) By closing the flap or valve on discharge side.b) Relieving part of the liquid flowing from discharge space to thesuction space.c) Changing RPM of the motor (if it possible). 4 5. Q. a) From what material is the WEAR RING made from?b) What is the allowable clearance for the WEAR RING?c) Sketch at least three wear ring types? A. A) WEAR RING MATERIAL: Aluminum, Bronze, Brass, Carbon- fiber, Vein forced thermoplasticmaterial Stainless alloys. b) The clearance between the impeller and the casingWearing ring must be a maintained as directed by the manufacturer. When clearances exceed the specified amount, the casing-wearing ring must be replaced. The clearance given for wear rings is often a source of contention especially when dealing with on-ship made rings. A clearance of 1/1000 of the diameter of the bore is often quoted although this may be very difficult to achieve in practice 2-STAGE SELF PRIMING P/PSymbolsClearance in MMOn theDrawingManufacOverhaul Max. ture Clearanc available size e. clearanc newIntermed e. cond.iaterepair.1-STAGE NON SELF PRIMING P/P 5 6. 1-STAGE NON-SELF PRIMING P/PSymbol Clearance in MM QOn thedrawingm/hMANUFACTURE Max. Max.SIZEavailabl availabl NEW COND.eeclearanc clearance. e. 6 7. Q.Wear ring types:A. There are various types of wearing-ring designs, and selection of the most desirable type depends on the liquid being handled, the pressure differential across the leakage joint, the surface speed, and the particular pump design. In general, centrifugal-pump designers use the ring construction they have found suitable for each particular pump service. The most common ring constructions are the flat-type, the L- type and U- type. Q. What will happen when a centrifugal pump will turn in opposite direction?Will the pump build up pressure? And what will the power gauge show? A.When the centrifugal pump turns in the opposite direction of rotation, it can cause the following: a) Reduction in capacity b) Pressure droop c) Increased load high current Q.If the clearance of the wear ring increases, will the load increase, or decreases?A. If the clearance becomes too large, the pump efficiency will be reduced, causing heat and vibration problems. When the clearance between the wear ring increases, it will cause part of the liquids volume to pass over from the discharge space to the suction space. It will create an internal resistance. The pump must to wear down (overcome) the resistance of its owntransferring liquid and also resistance of the leakages. The pumpconsumes more energy. The load will be increased. It will be indicate on the Ampere Meter.7 8. Q. What types of bearings are used on a CENTRIFUGAL PUMP?A. ; Journal ThrustSupportSupport Thrust bearing:bearing.bearingbearing Bearing Made of Dbl. RowSingle Single row- Dbl. row bronze or Rollerrow-ball rollerBall bearing rubberbearing bearingbearing Heavy-Deep dutyGroove angular Ball contact bearing ball bearing 8 9. Q. Give a number of examples for centrifugal pumps that are used on the vesselwith a NON-RETURN VALVE on the discharge line.A.1) Sea water cooling pump2) F.W. central cooling pump3) Fire Fighting and General service pump4) Boiler feed and circulating pump5) HT cooling pumpQ. What is the significance of checkingPRESSURE TEST, on?A centrifugal pump? A.Pressure test =Head test it is measuring of KINETIC ENERGY. Significance of using the head term instead of the pressure termThe pressure at any point in a liquid can be thought of as being caused by aVertical column of the liquid due to its weight. The height of this column iscalled the static head and is expressed in terms of feet of liquid.The same head term is used to measure the kinetic energy created by thepump.In other words, head is a measurement of the height of a liquid column that the pump could create from the kinetic energy imparted to the liquid. Imagine a pipe shooting a jet of water straight up into the air, the height the water goes up would be the head. The head is not equivalent to pressure. Head is a term that has units of aLength or feet and pressure has units of force per unit area or pound perSquare meter.The main reason for using head instead of pressure to measure a centrifugal pumps energy is that the pressure from a pump will change if the specific gravity (weight) of the liquid changes, but the head will not change. Pressure to Head Conversion formula The static head corresponding to any specific pressure is dependent upon the weight of the liquid according to the following formula: Head= Pressure (PSI) 2.31Specific GravityQ. How do we check CAPASITY of the centrifugal pump?9 10. A. There are two methods to carry out a capacity test for a centrifugal pump. a) Calculation by means of formula: Q (m/h) Q=mvAm- mass of fluid in (kg)v- velocity of flow in (m/sec)A-area of the pipe in(m) OR: Q (feeet/h)Q=449vAv- velocity of flow in (feet/sec.)A-area of the pipe in(feet) b) In order to measure the capacity, we should fill the specific volume (tank), which is calibrated by sounding table.Time of filling must be noted and regarded to this volume.Q. In what way can we cool a mechanical seal?A. Where mechanical shaft seals are used, the design ensuresthat positive liquid pressure is supplied to the seal faces under allconditions of operation and that there is adequate circulation ofthe liquid at the seal faces to minimize the deposit of foreignmatter on the seal parts. a) Cooling water is supplied from the discharge side of the pump. b) Cooling liquid is supplied from the external source:(central coolingwater system or M.E. Jacket cooling system). Those pump usu