Pressure build up in gearbox

[Mario11]

I have a mechanical linear actuator that is a ballscrew mechanism with an oil (Mil-H-5606) filled gearbox.
Can someone be so kind to explain why there is pressure build up in the gearbox?

How can I theoretically determine what the optimum oil fill volume for the gearbox should be? The unit is exposed to temperatures of 70º F, 90º F, and 120º F.

We have been experiencing external leakage with no direct cause found with any of the components. I am wondering if the change in pressure is due to thermal expansion of the air trapped in the unit assembly.

How do I calculate the change in volume of air and the change of volume of oil, unconstrained, over the temperature range referenced above?

I appreciate any input,

Mario

 

[unclesyd]

It is not uncommon for pressure buildup in a geabox.

It is the temperature of the oil in the gearbox while operating at your stated temperature that be be the root of the problem.

You will need to consult the gearbox manufacturer as the level normally depends on the internal construction.

There are devices, vents and breathers, to alleviate this problem. These can be used until you can get the correct oil level for your box.

http://www.alemite.com/catalog/details.aspx?identifier=fittings_airventvalves

http://www.alemite.com/catalog/details.aspx?identifier=fittings_breathers