I am working on a hydraulic system that is powered by an air-hydraulic piston pump, the pump uses pneumatic pressure to drive a piston which then pressurizes the hydraulic system. The system needs to be revised to have the air supply to these pumps cut off as soon as the hydraulic pressure reaches the needed 500 bar, in order to stop the pumps and prevent unnecessary wear or pressure. I looked for hydraulically actuated valves for pneumatic systems but could not find any, therefore my question is if these valves actually exist or if I should look for a different method?
A better approach would be continuously regulating (limiting) air pressure supplied to the pump, rather than suddenly shutting off air once hydraulic pressure reaches 500 bar. No need for hydraulic pressure to actuate a pneumatic valve in this case. Typical example:
Back to the original question, it's certainly possible to actuate pneumatic valves using hydraulic pressure if needed. However solenoids or air pressure is more practical in most cases. One exception would be large steam valves which use hydraulic actuation: