Proper operating temp for servo hydraulics?

[notkeith]

Proper operating temperature for servo hydraulic systems (3000 PSI system pressure) has always been a debate around here. If you look a Moog specifications, you'll find that their valves are good up to 275 deg F. When you look up specs for Mobil DTE 25, the viscosity charts suggest temperatures up to 200 deg without serious break down. I've personally been taught (years past) that for servo valve applications, the operating oil temp should be between 120 deg F (very low) up to 160 deg F (very high), with desired range between 130 and 150 deg F. It seems hard to find any "hardcore" information on this topic.

What is your opinion?

Thanks,
Keith Urban
Sr. Product Test Engineer, Dana Corp.