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Differences between fixed displacement pump and variable displacement pump?
the main difference between them is the way that energy is added to the fluid to be converted to pressure increase. In dynamic pumps, energy is added to the fluid continuously through the rotary motion of the blades. These rotating blades raise the momentum of fluid and the momentum then is converted to pressure energy through diffuser in pump outlet. In positive displacement pumps, the energy is added periodically to the fluid. the pump has reciprocating motion by pistons for example. When the fluid enters the pump through valves, the reciprocating piston begins to press the fluid resulting in going out of the pump with pressure rise.
Disadvantage of positive displacement pump?
THIS FORM OF transferring an emotional response
What is a non-positive displacement pump?
A hydraulic pump that uses an impeller or propeller to move fluid by momentum, as opposed to a positive displacement pump, which moves discrete quantities of fluid with each rotation. A typical application of a non-positive displacement pump is the coolant pump, or water pump, on a radiator-cooled engine.The most common types of mobile hydraulic (hydraulic oil systems) pumps that one might come across are:Vane type (positive displacement, open center system)Gee Roller (positive displacement, open center system)Gear type (positive displacement, open-center system)Radial piston (positive displacement, closed center, destroking and pressure compensating)Axial piston (positive displacement, closed center, destroking, pressure compensating and load sensing)The open center system pumps being positive displacement must have a dump valve, bypass, or pressure relief on the outlet side of the pump because of constant flow production. For example, if you were to put an on-off valve on the outlet side of a positive displacement open-center system and if you turned that valve to "off" You would either hit a system "stall" pressure or have a broken housing and/or lines.The closed center systems will "destroke" (stop pumping) when there is no demand for pressure oil. This allows for decreased horsepower demands and lower sump oil temperature.Examples of non-positive displacement pumps are:Turbine pumpsImpeller (centrifugal) found in engine cooling systems, liquid transfer pumps, and dredging systems.Any pump that does not require a relief, dump, or bypass valve when outlet flow or pressure is restricted or stopped.With these examples it is easy to assume that they are open center systems, however, being non-positive displacement an individual could shut off a valve on the outlet side of these systems and avoid system damage. This is due in most part to larger clearances within the pump, which allow for a certain amount of a "calculated leak" or "slippage" as another individual stated. Shutting off the outlet side will strain the system a little but it should be accepted to system specifications. This examples plays out in the cooling system of a vehicle every time the engine temperature is below operating temp. The water pump is being turned whenever the engine is running but until the thermostat (our hypothetical valve) opens, the impeller of the water pump must slip as it continues to try and build flow.
Shutting the discharge of an air operated reciprocating pump will cause the pump to do what?
stall
Types of positive displacement pump?
gear pump, crescent gear pump, axial-piston pump, radial-piston pump, linear-piston pump, & vane pump Also, fuel injection pumps such as linear piston pumps and rotary piston pumps.
