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I need to do some calculation to find out whether my design works. I may use oil/water/air in my pneumatic cylinder (or you can call it hydraulic cylinder). Assume I have just a cylinder and I put oil into the chamber to raise a weight. My question is how much of volume will reduce when the weight is x kg (Let assumes x = 20). Also what if I change the oil to water or air.

From my knowledge air is easier to calculate, because I can use the ideal gas law. Am I right?


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up vote 2 down vote accepted

Air is by ideal gas law, for water, you need the bulk modulus which is $2.2 \times 10^9$ Pascals. This means that at a pressure P Pascals slightly more than atmospheric pressure, you reduce the volume by P divided by this number.

According to this web page, oil has a bulk modulus of roughly 200,000 Psi, which is about $1.5 \times 10^9$ Pascals.

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I love your answer. It is simple enough for non-expert (like me) to understand. Thanks – Marco Aug 29 '12 at 15:08

You must specify wether the temperature is constant or if there is some heat exchange. Then you just have to use the isothermal compressibility or adiabatic compressibilty factor.

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Thanks for your help – Marco Aug 29 '12 at 15:07

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