How to Select Hydraulic Pumps
Image Credit: Haskel International, Inc. | Grainger Industrial Supply | Continental Hydraulics
Hydraulic pumps are positive displacement pumps which pressurize hydraulic fluid in order to do work. They are powered by mechanical energy sources which apply force directly to a movable volume of liquid. Hydraulic pumps are simple pumps, but are able to achieve some of the highest pressures among pump types.
Operation
Hydraulic pumps operate on the principle of positive displacement. Positive displacement pumps use expanding and contracting cavities to move fluids. In the case of hydraulic pumps, these cavities apply force directly to a hydraulic fluid, allowing it to exit the pump at high pressures. There are many variations of hydraulic pumps, operating as either rotary or reciprocating.
- Rotary pumps are typically characterized by medium flow rates and low to medium head. They provide a smooth flow and are best suited for clean, non-abrasive, viscous fluids. Subtypes of rotary pumps include screw, peristaltic, gear, and rotary vane pumps.
- Gear pumps contain few moving parts and are the ideal choice for clean oils and other clean, high viscosity fluids.
- Peristaltic pumps require no seal and have no leakage, making them a good choice for handling disinfectants, corrosives, and media containing solids.
- Rotary vane pumps are able to handle thick and thin liquids well, making them ideal for applications handling multiple clean fluids of varying viscosities.
- Screw pumps provide the highest flow rates of positive displacement pumps. They can handle oils, fuels, and other high viscosity liquids.
- Reciprocating pumps are typically characterized by low flow rates and high head. They provide a pulsed flow able to handle dirty, tacky, and viscous liquids. Subtypes include diaphragm, piston, and plunger pumps.
- Diaphragm pumps are seal-less pumps which can run dry and can handle a wide range of liquids, including fluids containing solids and corrosives.
- Piston pumps can provide very high pressure and are best suited for high head applications involving abrasive liquids.
- Plunger pumps provide the best means to achieve very high pressures. They are best suited for water and other thin liquids.
Specifications
There are a number of specifications to consider when selecting hydraulic pumps.
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Head defines the energy supplied to liquid (per unit weight) by the pump. It is expressed as a column height of liquid (either vertical lift or suction), given in feet of head (ft).
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Pressure describes the operational pressure of the pump. It is usually given in pounds per square inch (psi) or bar.
- Operating speed is the speed at which the pump’s moving parts rotate, expressed in revolutions per minute (rpm) or similar terms.
- Horsepower indicates the output power of the pump, and is dependent on the pressure and flow of the fluid through the pump. It is measured in units of horsepower (hp).
- Power rating indicates the power required to operate the pump, measured in Watts (W) or horsepower (hp).
- Flowrate describes the rate of volume discharge through the pump, usually given in gallons per minute (gpm) or gallons per hour (gph).
- Outlet diameter is the size of the discharge or outlet connection of the pump. Inner diameter (I.D.) describes the size of the inner opening while outer diameter (O.D.) specifies the entire opening size including the pipe thickness.
- Operating temperature defines the range of temperatures or temperature limit of the media handled by the pump.
- Maximum fluid viscosity is the viscosity the hydraulic pump can accommodate, measured on the basis of the fluid's resistance to shear. It is measured in centipoises (cP).
For a more in depth understanding of pump specifications, performance curves, and operation, visit the Industrial Liquid Handling Pumps information page on GlobalSpec.
Applications
Hydraulic pumps are designed to generate high enough fluid pressures to do work. Applications include construction equipment (e.g. backhoes, forklifts), elevators, and industrial presses.
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