Assignment # 4Pumps:A pump is a device used to move fluids (liquids or gases) or sometimes slurries by mechanicalaction. Pumps can be classified into three major groups according to the method they use to movethe fluid: direct lift, displacement, and gravitypumps. Pumps must have a mechanism whichoperates them and consume energy to perform mechanical work by moving the fluid.The activating mechanism is often reciprocating or rotary. Pumps may be operated in manyways, including manual operation, electricity,a combustion engine of some type, and wind action.There are mainly two types of pumps Positive displacement pumps Variable displacement pumpsPositive Displacement Pumps:It operates with the alternately filling a capacity and displacing a given volume of the liquid. Itdelivers a constant volumes against varying heads. A Positive Displacement Pump cannot beoperated against a closed valve on the discharge side of the pump. If a Positive DisplacementPump is allowed to operate against a closed discharge valve it will continue to produce flowwhich will increase the pressure in the discharge line until either the line bursts or the pump isseverely damaged or both.Reciprocating pumps:Reciprocating compressors are either single- or double-acting. In single-acting machines thecompression takes place on only one side of the piston; double-acting machines use both sides ofthe cylinder for compression.
A hand pump that moves fluids during both strokes of the pump handle. A wobble pump is anexample of a double-acting hand pump.Axial piston Pump:An axial piston pump is a positive displacement pump that has a number of pistons in a circulararray within a cylinder block. It can be used as a stand-alone pump, a hydraulic motor or anautomotive air conditioning compressor. An axial piston pump has a number of pistons (usuallyan odd number) arranged in a circular array within a housing which is commonly referred to as acylinder block, rotor or barrel. This cylinder block is driven to rotate about its axis of symmetryby an integral shaft that is, more or less, aligned with the pumping pistons (usually parallel butnot necessarily).Double Acting Reciprocating pumps:This type of pump operates in exactly the same way as the single acting with respect to its action.The difference is, that the cylinder has inlet and outlet ports at each end of the cylinder. As thepiston moves forward, liquid is being drawn into the cylinder at the back end while, at the frontend, liquid is being discharged. When the piston direction is reversed, the sequence is reversed.With a double acting pump, the output pulsation is much less than the single acting.Variable displacement pumps:It is the type of pumps in which volume is changed with by changing pressure, discharge andhead.Centrifugal pump:A centrifugal pump is a rotodynamic pump that uses a rotating impeller to increase the pressureand flow rate of a fluid. Centrifugal pumps are the most common type of pump used to moveliquids through a piping system.The fluid enters the pump impeller along or near to the rotating axis and is accelerated by theimpeller, flowing radially outward or axially into a diffuser or volute chamber, from where itexits into the downstream piping system. Centrifugal pumps are typically used for large dischargethrough smaller heads. Centrifugal pumps are most often associated with the radial flow type.However, the term "centrifugal pump" can be used to describe all impeller type rot dynamicpumps including the radial, axial and mixed flow variations.
Radial flow pumps:Often simply referred to as centrifugal pumps. The fluid enters along the axial plane, isaccelerated by the impeller and exits at right angles to the shaft (radially). Radial flow pumpsoperate at higher pressures and lower flow rates than axial and mixed flow pumps.Axial flow pumps:Axial flow pumps differ from radial flow in that the fluid enters and exits along the samedirection parallel to the rotating shaft.The fluid is not accelerated but instead "lifted" by the action of the impeller. They may be likenedto a propeller spinning in a length of tube. Axial flow pumps operate at much lower pressures andhigher flow rates than radial flow pumps.Mixed flow pumps:Mixed flow pumps, as the name suggests, function as a compromise between radial and axialflow pumps, the fluid experiences both radial acceleration and lift and exits the impellersomewhere between 0–90 degrees from the axial direction. As a consequence mixed flow pumpsoperate at higher pressures than axial flow pumps while delivering higher discharges than radialflow pumps. The exit angle of the flow dictates the pressure head-discharge characteristic inrelation to radial and mixed flow.jet pumps:This uses a jet, often of steam, to create a low pressure. This low pressure sucks in fluid andpropels it into a higher pressure regionSubmersible pump:A submersible pump (or electric submersible pump (ESP)) is a device which has a hermeticallysealedmotor close-coupled to the pump body. The whole assembly is submerged in the fluid to bepumped.
The main advantage of this type of pump is that it prevents pump cavitation, a problem associatedwith a high elevation difference between pump and the fluid surface. Submersible pumps pushfluid to the surface as opposed to jet pumps having to pull fluids.Gear pump:A gear pump uses the meshing of gears to pump fluid by displacement. They are one of the mostcommon types of pumps for hydraulic fluid power applications. Gear pumps are also widely usedin chemical installations to pump fluid with a certain viscosity.There are two main variations; external gear pumps which use two external spur gears, andinternal gear pumps which use an external and an internal spur gear. Gear pumps are positivedisplacement (or fixed displacement), meaning they pump a constant amount of fluid for eachrevolution. Some gear pumps are designed to function as either a motor or a pump.Ram Pumps:A ram pump requires hydraulic pressure to operate the pump (Not electricity!), so a drop or"head" is mandatory to make the pump work. The ram pump then uses the energy generated bythe weight of the water to continuously pump a fraction of it uphill up to 10 times the "head" orfall feeding the pump. When the ram pumps poppet valve (the only moving part) is open, waterflows downhill through the supply pipe to the pump and escapes out the open valve. That is wastewater, and is utilized to generate the kinetic energy required to pump some of the water up thedelivery pipe. As the water gains velocity in the supply, or drive pipe, it causes the poppet to snapshut, which causes hydraulic pressure to peak immediately (a "water hammer" effect), whichforces some water through a check valve, and into the delivery pipe. This cycle repeats itselfabout once a second.