An external relief valve in the discharge line, with a return line back to the suction line or supply tank provides increased safety.Ī positive-displacement pump can be further classified according to the mechanism used to move the fluid: The internal valve is usually used only as a safety precaution. The pump manufacturer normally has the option to supply internal relief or safety valves. The relief valve can be internal or external. A positive-displacement pump operating against a closed discharge valve continues to produce flow and the pressure in the discharge line increases until the line bursts, the pump is severely damaged, or both.Ī relief or safety valve on the discharge side of the positive-displacement pump is therefore necessary. However, a slight increase in internal leakage as the pressure increases prevents a truly constant flow rate.Ī positive-displacement pump must not operate against a closed valve on the discharge side of the pump, because it has no shutoff head like centrifugal pumps. Thus, positive-displacement pumps are constant flow machines. Positive-displacement pumps, unlike centrifugal, can theoretically produce the same flow at a given speed (rpm) no matter what the discharge pressure. Positive-displacement pump behavior and safety The volume is constant through each cycle of operation. Liquid flows into the pump as the cavity on the suction side expands and the liquid flows out of the discharge as the cavity collapses. Some positive-displacement pumps use an expanding cavity on the suction side and a decreasing cavity on the discharge side. See also: Vacuum_pump Positive-displacement pumps Lobe pump internalsĪ positive-displacement pump makes a fluid move by trapping a fixed amount and forcing (displacing) that trapped volume into the discharge pipe.
In biology, many different types of chemical and biomechanical pumps have evolved biomimicry is sometimes used in developing new types of mechanical pumps. A pump that does not fit this description is simply a single-stage pump in contrast. Terms such as two-stage or double-stage may be used to specifically describe the number of stages. When a pump contains two or more pump mechanisms with fluid being directed to flow through them in series, it is called a multi-stage pump. In the medical industry, pumps are used for biochemical processes in developing and manufacturing medicine, and as artificial replacements for body parts, in particular the artificial heart and penile prosthesis. Mechanical pumps serve in a wide range of applications such as pumping water from wells, aquarium filtering, pond filtering and aeration, in the car industry for water-cooling and fuel injection, in the energy industry for pumping oil and natural gas or for operating cooling towers and other components of heating, ventilation and air conditioning systems.
A small, electrically powered pump A large, electrically driven pump for waterworks near the Hengsteysee, GermanyĪ pump is a device that moves fluids ( liquids or gases), or sometimes slurries, by mechanical action, typically converted from electrical energy into hydraulic energy. For other uses of "pump" or "pumps", see Pump (disambiguation).
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