951 hydraulic tank

Hi, Cat 951.
My understanding is that these systems are not vented, that they build up pressure in the tank as the oil heats up and this aids supply to the pump. Even after they have cooled down, if you loosen the tank cap, you will very often hear air escaping under pressure from inside the tank. If the system has been over-filled somehow, you may even have oil coming out of the cap when it is loosened.

Just my 0.02. Others may be able to give better information.

Thank you for your response.
I understand what you mean, and I agree that the pressure can help the operation of the pump, but if there is an oil overheating or a malfunction in the system, there is a risk that some component explode?

Deas is right on--thats how my 941b system is--i would assume at a very high pressure--say 2000 psi or so you run the risk of blowing a hose or something---there may be a high pressure relief somewhere in the system??

Cat uses a closed system with air cushion to prevent/reduce hydraulic shock.