Centrifugal Pump.docx

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Centrifugal pumpDevice for moving liquids and gases. The two major parts of the device are the impeller (a wheel with vanes) and the circular pump casing around it. In the most common type, called the volute centrifugal pump, fluid enters the pump at high speed near the centre of the rotating impeller and is thrown against the casing by the vanes. The centrifugal pressure forces the fluid through an opening in the casing. This outlet widens progressively in a spiral fashion, which reduces the speed of the fluid and thereby increases pressure. Centrifugal pumps produce a continuous flow of fluid at high pressure; the pressure can be increased by linking several impellers together in one system. In such a multistage pump the outlet for each impeller casing serves as the inlet to the next impeller. Centrifugal pumps are used for a wide variety of purposes, such as pumping liquids for water supply, irrigation, and sewage disposal systems. Such devices are also utilized as gas compressors.Centrifugal forcequantity, peculiar to a particle moving on a circular path, that has the same magnitude and dimensions as the force that keeps the particle on its circular path (the centripetal force) but points in the opposite direction.Centrifugal PumpImpellerAn impeller (or impellar) is a rotor inside a tube or conduit used to increase the pressure and flow of a fluid.

The working principle of centrifugal pump

The impeller installs in the pump housing in 2, and fastens in the pump spindle on 3, the pump spindle leads directly by the electrical machinery. The pump housing central has a liquid inspiration 4 and the boost 5 connections. The liquid 6 and the boost enter in the pump after the bottom valve. In pump housing liquid escapement 8 and education tube 9 connections. Starts before the centrifugal pump, in the pump housing fills the liquid which transports; after the start, after the start, the impeller leads the high speed rotation by the axis, liquid between leaf blades also must along with the rotation. Under the centrifugal force function, the liquid is thrown from the impeller center and obtains to the outflow boundary the energy, by leaves the impeller outflow boundary to enter the worm type pump housing high speed. In the volute, the liquid decelerates as a result of the flow channel gradual expansion, also transforms the partial kinetic energy into the static pressure energy, finally by the high pressure inflow exit pipe, delivers to needs the place. Liquid when flows to the outflow boundary by the impeller center, in the impeller center has formed certain vacuum, because above the storage tank liquid level pressure is bigger than the pump inlet place pressure, the liquid continuously is then pressed in the impeller. Obviously, so long as the impeller rotates unceasingly, the liquid then can unceasingly and discharges by the inspiration.

Based on number of impeller/s in the pump:

PumpA pump is a machine that imparts energy to a liquid to increase its pressure and move it from one point to another. We used the term liquid (not fluid ) because the word pump is universally used to refer to a machine that pumps liquid whereas one that handles air, gas, or vapor, is specifically referred to as air pump, vacuum pump, compressor, blower, or fan.

In this web site the word pump is used to refer to machinery that handles liquid. It is important to make this distinction because air, gas, or vapor is an "enemy" of a pump that impairs its performance and operation. A pump, in its universal meaning, should not be used for handling air, gas, or vapor.A typical pump has hundreds of parts. No matter how simple or complex some pumps are, their major parts are designed to perform specific functions regardless of their sizes and shapes. The major parts are: casing impeller shaft seal bearing coupling

CasingThe casing (or case) contains the liquid and acts as a pressure containment vessel that directs the flow of liquid in and out of the pump. In most cases the casing includes the suction and discharge nozzles of the pump that connect it to the external piping. In some vertical pumps the casing may be referred to as bowl, and in some small pumps they may it call it housing.

ImpellerThe impeller is a vaned-disk (or disc) mounted on the shaft. Its function is to increase the pressure of the liquid by means of its rotating action. The impeller may be of open, semi-open, or enclosed type, and may have anywhere between two to ten vanes. It may also be of single, or double, suction design.

SealA pump may be provided with one of two types of sealing elements - packing rings or mechanical seal. The sealing elements prevents the leakage of the pumped liquid into the atmosphere.

BearingsThe functions of the bearings are to support the weight of the shaft (rotor) assembly, to carry the hydraulic loads acting on the shaft, and to keep the pump shaft aligned to the shaft of the driver.

CouplingThe function of a coupling is to connect the pump shaft and the driver shaft, and to transmit the input power from the driver into the pump.

Types of centrifugal pumps

Centrifugal pumps can be grouped into several types using different criteria such as its design, construction, application, service, compliance with a national or industry standard, etc. Thus one specific pump can belong to different groups and oftentimes this becomes descriptive of the pump itself. Some of these groups are:Based on number of impeller/s in the pump:Single stage - pump has one impeller only; for low head serviceTwo-stage - pump has two impellers in series; for medium head serviceMulti-stage - pump has three or more impellers in series; for high head service

The number of impellers, not the number of volutes, determines the number of stages. Thus a pump with 4 volutes but only 3 impellers is normally referred to as a 4-stage pump destaged to 3-stage, or 4/3-stage.

Based on impeller suction:Single suction - pump with single suction impeller (impeller has suction cavity on one side only); simple design but impeller is subjected to higher axial thrust imbalance due to flow coming in on one side of impeller only.

Double suction - pump with double suction impeller (impeller has suction cavities on both sides); has lower NPSHR than single suction impeller. Pump is considered hydraulically balanced but is susceptible to uneven flow on both sides of impeller if suction piping is not done properly.

In a pump with more than one impeller the design of the first stage impeller determines if the pump is considered single or double suction type.

Based on type of volute:Single volute - pump volute has single lip which is very easy to cast. Is usually used in small low capacity pumps where a double volute design is impractical due to relatively small size of volute passageway which makes obtaining good quality commercial casting difficult. Pumps with single volute design have higher radial loads.

Double volute - pump volute has dual lips located 180 degrees apart resulting in balanced radial loads; most centrifugal pumps are of double volute design.

Based on nozzle location:End suction/top discharge - the suction nozzle is located at the end of, and concentric to, the shaft while the discharge nozzle is located at the top of the case perpendicular to the shaft. Pump is always of an overhung type and typically has lower NPSHR because the liquid feeds directly into the impeller eye.

Top/top nozzles -the suction and discharge nozzles are located at the top of the case perpendicular to the shaft. Pump can either be overhung type or between-bearing type but is always a radially-split case pump.

Side/side nozzles - the suction and discharge nozzles are located at the sides of the case perpendicular to the shaft. Pump can either be an axially or radially split case type.

Based on shaft orientation:Horizontal - pump with shaft in horizontal plane; popular due to ease of servicing and maintenance.

Vertical - pump with shaft in vertical plane; ideal when space is limited or of a premium, or when pumping from a pit or underground barrel to increase the available NPSH.

Based on orientation of case-split:Axial split - pump case is split axially; the upper half is called the upper or top case, the lower half is called the lower or bottom case. The case cannot be supported at shaft centerline because of the case split; is usually limited to temperature up to 450 degrees F to avoid misalignment because of uneven thermal expansion from shaft centerline. The flat case gasket and irregular bolting pattern makes containing the bolt stress difficult hence it is limited in its hydrostatic test and allowable working pressure.

Radial split - pump case is split radially; the split parts are usually referred to as case and cover; can be supported at shaft centerline for even thermal expansion and is the preferred construction for high temperature application. The confined case gasket and circular bolting pattern makes containing the bolt stress more manageable hence it can be designed for higher hydrostatic test and allowable working pressure.

Based on bearing support:Overhung - the impeller overhungs on one end of shaft which is unsupported by a bearing; usually has lower NPSHR because there is no shaft blockage at the impeller eye. The trade-off is that pump has higher shaft deflection.

Between-bearing - the shaft has bearing support on both ends, thus impeller is located in between-bearings. Pump has lower shaft deflection than overhung pump but usually has higher NPSHR because shaft is blocking the impeller eye and shaft diameter at the impeller is usually of larger size.

Based on shaft connection to driver:Close-coupled - the impeller is mounted on the driver shaft which is of special design