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Hydraulic systems

  1. May 8, 2007 #1
    To all:

    I’m studding hydraulic systems and it call my attention that in between cycles, when there is no need of pressure, the pump keeps pumping fluid at high pressure and since the processes doesn’t need it, the fluid is sent back to the tank over an over again until the processes needs pressure again.

    This seems to me as a huge waste of electrical energy, because the pump is active all day long but is only useful half the time at the most. So why the systems are designed this way? Is there a reason that I’m not seeing? Wouldn’t it be better to turn off the pump in between cycles?

    I’ll appreciate your opinions

  2. jcsd
  3. May 8, 2007 #2


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    Science Advisor

    It's not that much of a waste. Having a relief redirect flow back to the tank is not a high pressure operation. There is very little load on the pump in that case since there is no real pressure demand (unless the relief itself requires a pressure build). In many systems, it is a much tougher job to start up the system versus keeping it operating constantly. It really does depend on the system, the cycle time and other aspects of whether or not this happens.

    In some ways this does also serve a purpose in keeping the fluid moving and being constantly filtered.
  4. May 8, 2007 #3
    Not all systems have hydraulic fluid flowing constantly. In some systems when there aren't any valves directing the fluid to hydraulic cylinders/orbital motors/etc. the flow is simply dead headed. It would be as if you capped the pipe. What happens then is the pump simply quits pumping. Various arrangements can be made for this. Usually the pump does what is referred to as 'go out of stroke'. If the pump consists of a piston that rides on a cam we can apply hydraulic pressure to both sides of the piston which then can hold the piston away from the cam. The cam simply rotates without pushing the piston. When the system pressure drops when a valve is opened in order to run something the pressure on each side of the piston is no longer balanced and the pump 'goes back into stroke' and starts pumping.
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