What Functions Does The Hydraulic Pumps Perform

  • The   Hydraulic Pumps   converts mechanical energy into hydraulic energy. When the hydraulic pump is running, it performs two functions. First, its mechanical action creates a vacuum at the inlet of the pump, causing atmospheric pressure to force liquid from the storage tank into the inlet line of the pump. Secondly, its mechanical action transports this liquid to the outlet of the pump and presses it into the hydraulic system.

    The pump produces liquid movement or flow: it does not generate pressure. It generates pressure to produce the required flow rate, which is a function of the fluid flow resistance in the system. For example, for a pump that is not connected to the system (load), the fluid pressure at the pump outlet is zero. In addition, for pumps delivered to the system, the pressure will only rise to the level required to overcome the load resistance.

    Pump classification
    All pumps can be classified as positive displacement or non-positive displacement. Most pumps used in hydraulic systems are positive displacement pumps.

    Non-positive displacement pumps produce continuous flow. However, because it does not provide a reliable internal seal to prevent slippage, its output will vary significantly with changes in pressure. Centrifugal pumps and propeller pumps are examples of non-positive displacement pumps.

    If the output port of the non-positive displacement pump is blocked, the pressure will rise and the output will decrease to zero. Although the pumping element will continue to move, the flow will stop due to slippage inside the pump.

    In positive displacement pumps, the slip is negligible compared to the volumetric output flow of the pump. If the output port is blocked, the pressure will immediately increase to the point where the pump element of the pump or its casing will fail (it may explode if the drive shaft does not break first), or the pump's prime mover will stall.


    Positive displacement principle
    A positive displacement pump is a pump that displaces (delivers) the same amount of liquid in each rotation cycle of the pumping element. Due to the tight fit between the pumping element and the pump casing, it can be delivered constantly in every cycle. That is, the amount of liquid slipping through the pumping element in the positive displacement pump is the smallest and negligible compared to the theoretically highest possible delivery. Regardless of the pressure change during pump operation, the delivery volume per cycle remains almost constant. Please note that if the fluid slips severely, it indicates that the pump is not operating properly and should be repaired or replaced.

    Positive displacement pumps can be fixed displacement or variable displacement. The output of the fixed displacement pump is kept constant at a given pump speed during each pumping cycle. The output of the variable displacement pump can be changed by changing the geometry of the displacement chamber.

    Other names describing these pumps are hydrostatic pumps for positive displacement and hydrodynamic pumps for non-positive displacement. Hydrostatic pressure means that the pump converts mechanical energy into hydraulic energy with a smaller liquid volume and speed. In hydrodynamic pumps, the liquid velocity and motion are large; the output pressure actually depends on the speed at which the liquid flows.

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