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Hydraulic oil not susceptible to temperature fluctuation

  1. Jan 28, 2014 #1
    Im having an issue with a manual pump opening an actuator. It opens fine and holds pressure until the temperature starts to drop. My question is does anyone know of any hydraulic oil that is not susceptible to condensing when temperature drops?
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  3. Jan 28, 2014 #2


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    What do you mean by 'condensing'? Isn't oil by definition already a liquid?
  4. Jan 29, 2014 #3


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    My guess is that the O-ring or piston seals on the cylinder or pump are leaking when they are cold and hard.

    If you are having problems with water condensation in hydraulic oil then maybe you chould consider using one of the glycol based hydraulic fluids.
  5. Jan 29, 2014 #4
    What is the actual problem - you have listed 2 problems. 1.the actuator opening 2. the actuator holding
  6. Jan 29, 2014 #5
    Its like gas when its hot it expands and when its cold is "gets smaller" so in my case when it gets cold and the fluid shrinks it opens more room and drops in pressure slowly until the temperature stays constant. With our system once we drop 10% of the set pressure we get a failure alarm. My problem is when my hydraulic fluid gets cooled from its starting temp it is contracting therefore dropping in pressure
  7. Jan 29, 2014 #6


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    You will need some method for control of the hydraulic pressure over time if you need to maintain a certain pressure range over a range of temperatures. All hydraulic fluids will have some amount of thermal expansion/contraction.

    By the way the system would not necessarily have to be electronic with sensors; you might be able to develop (of identify) a pressure stabilizing hydraulic circuit. For example a spring-loaded piston capable of maintaining pressure with volume expansion/contraction could solve the problem.
  8. Jan 29, 2014 #7


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    My guess is that your hydraulic lines are long, high capacity, metal tubing that is driving a relatively small capacity actuator.

    It could be countered with a small hydraulic accumulator or by replacing metal lines with rubber hydraulic hose that can act as an accumulator because they are more elastic than metal lines.

    A much thinner line to the actuator could also resolve the problem because the ratio of the volumes is important.

    On a double acting system, the contraction effect could also be countered with a pilot operated lock valve on the actuator.

    It is possible that the system worked when originally commissioned because some air was trapped in the line. Now that it has been bled, there is no accumulator effect. Can the air bubble situation be restored safely to test the hypothesis?
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