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Hydraulic pump/motor

  1. Apr 14, 2015 #1
    hey people. literally just joined, hehehe
    my question is, can a hydraulic pump be used as a hydraulic motor. i have an idea and want to have it operating using hydraulics rather than having shafts and gearboxes to transfere to work.
    any comments welcome, good or bad, but i prefere good....hehehe
    Last edited by a moderator: Apr 14, 2015
  2. jcsd
  3. Apr 14, 2015 #2

    jack action

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    From Wikipedia:
  4. Apr 14, 2015 #3
    Thanks Jack action.
    There is information there that I didn't know about.
  5. Apr 14, 2015 #4

    Randy Beikmann

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    What you are describing is a hydro-static transmission. The pump and motor can each be designed to be pump/motors, but they aren't necessarily that way, as jack action said.
  6. Apr 14, 2015 #5


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    Conceptually simple, but there are many traps for the beginner. Pumps will often have a big inlet because only atmospheric pressure is available to push oil into the pump chamber, it can have a smaller outlet.

    Pumps are usually designed to rotate in one particular direction. A hydraulic pump is designed to have a low and a high pressure side with seals to prevent it sucking air on the inlet side or weeping oil on the high pressure side.

    A hydraulic motor may be designed for bi-directional operation. It can be operated with positive pressure on both ports. Bidirectional motors will have a third connection to drain fluid to the reservoir tank that leaks past the internal seals.

    Hydraulic motors and pumps might get to 90% efficiency. A pump driving a motor will therefore have 90% * 90% = 81% efficiency. You will need to pay for that 19% inefficiency, you will also need an oil cooler to remove the 19% waste heat. A manual change gearbox will be closer to 98% efficient.
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