Anna GE 6253 - Sources of Hydraulic Power

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Sources of Hydraulic power Pumping Theory Pump Classification Pump is a machine or mechanical equipment which is required to lift liquid from low level to high level or to flow liquid from low pressure area to high pressure area Before you purchase a pump you must specify the type of pump and make sure it is given pressure capable of delivering given flowrate at a a A Pump Doing Work 1 pound 0 45 kg 1 gallon 3 78 liters 1 PSI POUND PER SQUARE INCH 0 07 kg cm2 or 0 06 bar It is often assumed that pumps create pressure but the sole purpose of pumps is Pumping theory to create flow Pressure is force per unit area and is created by resistance to flow A pump is a mechanism designed to produce the flow necessary for the development of pressure within the device operating principle of the pump is to convert mechanical energy to pressure Energy transfer the transfer of energy from the shaft to the impeller and from the impeller to the water Centrifugal force the force used to throw the water from the impeller The positive displacement hydraulic pump is a device that converts mechanical energy into hydraulic energy When driven by its motor prime mover it basically performs two functions Firstly it creates a partial vacuum at the pump inlet port This vacuum enables the atmospheric pressure to force fluid from the reservoir tank into the pump Secondly the mechanical action of the pump traps this fluid within the pumping cavities transports it through the pump and forces it into the hydraulic system Hydraulic Pumps Pumping Theory hydraulic energy The positive displacement hydraulic pump is a device that converts mechanical energy into When driven by its motor prime mover it basically performs two functions Firstly it creates a partial vacuum at the pump inlet port This vacuum enables the atmospheric pressure to force fluid from the reservoir tank into the pump flow Secondly the mechanical action of the pump traps this fluid within the pumping cavities transports it through the pump and forces it into the hydraulic system Pumps create flow not pressure It is often assumed that pumps create pressure but the sole purpose of pumps is to create Pressure is force per unit area and is created by resistance to flow Classification of Pumps pump types generally fall into two main categories Dynamic Centrifugal Pumps Energy is continuously added to increase the fluid velocities within the machine Hydrodynamic or non positive pumps They are used for low pressure high volume flow applications Normally their maximum pressure capacity is limited to 250 300 psi Reciprocating pumps Rotary pumps and Pneumatic pumps Hydrostatic or positive pumps Gear vane piston pumps little leakage or slippage between them High pressure capability up to 10 000 psi or higher Small compact size Positive Displacement Pumps Energy is periodically added by application of force to enclosed fluid containing volumes Positive displacement pumps have the internal working elements which make a very close fit together so that there is very High volumetric efficiency Small changes in efficiency Great flexibility of performance Positive displacement pumps are usually selected for their ability to handle high viscosity fluids at high pressures and relatively low flows as their efficiency isn t affected by pressure Positive displacement pumps are able to handle variations in pressure flow and viscosity and remain efficient unlike centrifugal pumps which do not operate well off the center of their curve Positive Displacement Machines Typical positive displacement pumps a tire pump b human heart c gear pump centrifugal pump Pump Variable piston pump Fixed gear pump In a roto dynamic pump a rotating impeller imparts energy to the fluid The most common type of roto dynamic pump is the centrifugal pump low pressure high volume flow applications Since they are not capable of withstanding high pressures there is little use in the fluid power field Their maximum pressure is limited to 250 300 psi This type of pump is primarily used for location to from one transporting fluids another Centrifugal and axial flow propeller pumps are the two most common types of dynamic pumps Dynamic Centrifugal Pump Dynamic pumps uses centrifugal force to develop velocity in the liquid being handled The velocity is then converted to pressure As kinetic energy is decreased pressure is increased This pressure difference drives the fluid through the system Dynamic Centrifugal pumps use a rotating impeller to create a vacuum in order to move fluid The pump s impeller rotates within the housing and reduces pressure at the inlet This motion then drives fluid to the outside of the pump s housing which increases the pressure enough to send it out the discharge Dynamic Centrifugal pumps to transfer of low viscosity fluids in high flow rate low pressure installations which makes them ideal for applications that require the pump to deal with large volumes The centrifugal pump design is often associated with the transfer of water but is also a popular solution for handling thin fuels and chemicals maintenance requirements and costs Dynamic Centrifugal pumps benefit from a simple design with few moving parts resulting in lower


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Anna GE 6253 - Sources of Hydraulic Power

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