Definition for Hydraulic Pumps
The mechanical device that is used to convert mechanical power into hydraulic energy is known as a hydraulic pump. The load that is responsible for the pressure is overcome with this device by creating sufficient power and generating a flow.
The hydraulic pump has two functions to perform during operation, allowing atmospheric pressure to push liquid into the inlet line from the reservoir to the pump by the mechanical action created vacuum at the pump. The other function it performs is that the pumps mechanical action supplies the liquid to the pump outlet and then forced into the hydraulic system.
Categories of a Hydraulic Pump
 Positive-displacement and non-positive-displacement is what hydraulic pumps can be classified into, though a majority of the hydraulic systems utilize positive-displacement. The slippage in the positive-displacement pump is minor compared to volumetric output flow of the pump.
Now if the output port were blocked the pressure in the pump would increase immediately causing the pumping element or its case to stop working or the pump's prime mover could stall or even explode incase the drive shaft does not break.
But in the non-positive-displacement pump a continuous flow is produced since a positive internal seal is not provided to avoid slippage and this causes the pressure top to vary, which indirectly or directly causes a variable output. Examples of non-positive-displacement pumps are propeller and centrifugal pumps.
Working, Functioning and Specifications of Hydraulic Pumps
The pump outlets receive a high-pressure fluid flow from hydraulic pumps that pressurize fluid and are powered by mechanical energy resources. The hydraulic pumps can work as a motor since it rotates in forward and reverse direction when powered by pressurized fluid. When looking for hydraulic pumps there are a few specifications that are required to be considered like housing materials, operational specification etc.
When considering operational specifications, there are two that are most important, the pump type, and the pump stage. The types of hydraulic pumps range from radial piston, axial piston, gears- internal and external, and vane. The axially mounted piston that is used in an axial piston pump pressurizes the fluid and the piston is moved through the chamber pressurizing the fluid by the mechanical motion from the pump's power source.
The fluid flow is directed from the inlet pipe to the outlet or discharge using port plates or check valves. Another point to remember is that a majority of the axial piston pumps are multi-piston. In the radial piston pump, as the name suggests, the pistons are mounted radially with reference to a central axis. It is a variation of the axially mounted piston using a number of pistons that are interconnected, typically in a star pattern.
The stroke length of the pistons, their size and number, determines liquid displacement by the pump. Moving the reaction ring to increase or decrease piston travel, varying eccentricity, can vary displacement. There are a variety of controls available to monitor this. The pistons are forced in the chambers and pressurize the fluid because of the piston movement that is sourced from the hydraulic pumps' power.
The gear pump is another type of hydraulic pump in which the flow is produced by carrying the fluid in between the two meshing gears teeth. The pump housing and wear or pressure plates (side plates) enclose the chambers formed between the adjoining gear teeth.
Below optimum conditions the volumetric efficiencies of gear pumps reach a maximum of 93%. There is a always a certain loss when fluid is pumped at a fixed pressure and variable volume because of the clearances run in between gear tooth crests, gear faces and housing. So in order that the gear pumps operate at their maximum rated speeds, the volumetric efficiency is kept low and leads to a poor flow.
A gear pump is differentiated into internal and external, the fluid is pressurized using internal gears in the internal gear pump. The fluids are forced through the pump outlet by turning the internal gears using the pump's power source. The internal gear pumps are compact units and so they are used as portable units. With respect to the external gear pumps the fluid is pressurized through the pump outlet using external gears and the external gears are also turned using the power source from the pump.
The vane pump pressurizes the fluid using a vane and the vane rotates using the pumps power source. A vacuum is created during the vane rotation as the rotor, which is enclosed in the chamber increases. As this takes place in the inlet side of the pump, the atmospheric pressure forces oil in the chamber and as the space reduces, liquid is forced out from the outlets. Considering the stages of the pumps, they are set at single, double, triple, four and many more stages.
Other Hydraulic Pump Specifications
The additional specifications that are included in the operation of a hydraulic pump are:
- Weight of the pump.
- Operating speed - The pump's moving parts rotation speed and denoted in revolutions per minute, or similar terms.
- Operating temperature - The pumps accommodation capabilities with relation to the fluid temperature range.
- Operating horsepower - This is dependent on the liquid flowing through the pump and its pressure and the measure of power the pump is competent of delivering.
- Maximum operating pressure - The pump outlets available maximum peak pressure available on an irregular basis.
- Continuous operating pressure - The outlet pumps maximum pressure available.
- Fluid Temperature- This is a specification that varies from every manufacturer and depends on the internal component materials
- Maximum fluid viscosity- The fluid's resistance to shear
- Maximum fluid flow
- Displacement per revolution
Units of Measurement in Hydraulic Pumps
Gallons/unit is unit of measurement for the volumetric flow, and the fluid viscosity unit is centipoises for the hydraulic pump. The centipoise is equal to one mill Pascal second or 0.01 poise and is a universal metric unit of dynamic viscosity.
CC or cubic centimeters is the unit of measurement for the fluid volume displaced per revolution. And a pound is the measurement unit for the weight of the hydraulic pump.
Uses of Hydraulic Pumps
The hydraulic pump is one of the main components used in manufacturing, construction, and machining equipment. The hydraulic pump affects the machineries precision, productivity, efficiency and basically the overall system performance. In order that the hydraulic pumps last longer and wear less there are a number of materials that are used in it's manufacturing and in different composition depending on the purpose it has to serve.
For high-pressure systems, high strength alloys and polymers are utilized, while for low-pressure systems less expensive and minimal pressure pumps are available. It is always practical to consider the machineries operating conditions and requirements prior to purchasing a hydraulic pump. There are a variety of manufacturers to choose from.
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