I currently run tandem 55GPH PA Biodiesel units. They are driven by a ford power steering pump by an old whirlpool washing machine motor. I heat way north of 250 Degrees (I had the paint on the drums smoking the other day to drive all the water out) and run as long as I can tend to it. I used to run using manual bypass valve but recently dropped 30 bucks on an agriculture type bypass relief valve. I run at 90 to 95 PSI because I like overkill, but I can GUARANTEE you, over pressure on PA Bio units WILL deform the rotors. I have ruined one, and another needs to be beat back out or replaced soon. Both rotor were deformed by accident when my wife grabbed the reliefe valve and moved it the wrong way. After I got on to her about it, I did it myself a few months later.