Views: 0 Author: Site Editor Publish Time: 2023-02-16 Origin: Site
A pump is a device that moves a fluid (liquid or gas) or sometimes a slurry by mechanical action,usually converting electrical energy into hydraulic energy.Mechanical pumps are used in a wide range of applications such as pumping water from wells, aquarium filtration, pond filtration and aeration, in the automotive industry for water cooling and fuel injection, in the energy industry for pumping oil and gas or for operational cooling Towers and other components of heating, ventilation and air conditioning systems.In the medical industry, pumps are used in the biochemical processes of developing and manufacturing drugs, and as artificial replacements for body parts, especially artificial hearts and penile prostheses.When a pump contains two or more pump mechanisms through which the fluid is directed sequentially, it is called a multistage pump.The number of stages can be specifically described using terms such as two-stage or double-stage.Pumps that do not fit this description are single stage pumps only.In biology, many different types of chemical and biomechanical pumps have been developed; biomimicry is sometimes used to develop new types of mechanical pumps.
Mechanical pumps can be submerged in the fluid they pump or placed outside of the fluid.Pumps can be divided into positivedisplacement pumps, pulse pumps, speed pumps, gravity pumps, steam pumps and valveless pumps according to their displacement methods.Pumps are divided into three basic types: positive displacement pumps, centrifugal pumps, and axial flow pumps. In a centrifugal pump, the direction of fluid flow changes by 90 degrees as it passes the impeller, whereas in an axial pump, the direction of flow is constant.
Positive displacement pumps move fluid by trapping a fixed volume and forcing (displacing) the trapped volume into a discharge line.
Some positive displacement pumps use an expanding chamber on the suction side and a reducing chamber on the discharge side. When the cavity on the suction side expands, liquid flows into the pump, and when the cavity collapses, liquid flows out of the discharge port.The volume is constant during each operating cycle.
Positive displacement pump behavior and safety
Unlike centrifugal pumps, positive displacement pumps can theoretically produce the same flow at a given speed (rpm), regardless of discharge pressure.Therefore, a positive displacement pump is a constant flow machine.However, as pressure increases, internal leakage increases slightly, preventing a truly constant flow rate.A positive displacement pump must not be run with the valve closed on the discharge side of the pump because it does not have a closing head like a centrifugal pump.A positive displacement pump running with the discharge valve closed will continue to produce flow and pressure in the discharge line will build until the line bursts, the pump is severely damaged,or both.Therefore, positive displacement pumps require a pressure relief valve or safety valve on the discharge side.Safety valves can be internal or external.Pump manufacturers often have the option to provide internal pressure relief or safety valves.Internal valves are usually only used as a safety precaution.External relief valve in discharge line, return line back to suction line or supply tank for added safety.
Positive displacement pumps can be further classified according to the mechanism used to move fluid:
Rotary positive displacement: internal or external gear pumps, progressive cavity pumps, lobe pumps, shuttle pulleys, flexible or sliding vanes, peripheral pistons, flexible impellers, helical twist roots (eg Wendelkolben pumps) or liquid ring pumpsReciprocating positive displacement: piston pump, plunger pump or diaphragm pump linear positive displacement:rope and chain pumps.