gerotor pump cavitation

"any tricks on shaping the georotor to prevent caviatation?"

Never heard that the shape of internal pump components of any pump design had anything to do with preventing Cavitation. Cavitation, in a typical pump installation, is due to attempting to move more oil than the pump inlet can handle when atmospheric pressure is the only accelerating force.

I have used oversize inlet plumbing, mouted tanks overhead, pressurized tanks as seen on many Mobile systems and ran oil with reduced viscosity such as 10W50 Engine oil.

Since you indicate size limitations the only possible way might be pressurizing the system inlet to force the increased flow due to higher than designed RPM. Some Mobile applications use the differential area of cylinders to do keep a tank pressurized.

The other possibility might be to use 80-90% of the circuit return oil to supply the pump inlet and only have a 10-20% change of tank oil. I've never heard of that being done but it could be workable if the system cycle is short or if an oil cooling system is already there or a possibility.

Cavitation is not only due to vapour. In hydraulics it is generated by the presence of air in the oil. If pressure decreases air is not any more as well solved and bubbles do form. One possibility is to analyse you reservoir if the turbulence of oil does not entrap too much air. The second one is to use part of return oil to make a jet pump an the inlet of the main stage and increase pressure in front of suction orifices.

I used this approach ones and it worked.

And, if pressurizing the reservoir or adding a device that pushes oil to the pump inlet or returning pumped oil to add in the inlet do not work, maybe it's time to design that pump with another stage to reduce the pressure diferential. Yeah, I know. This is the expensive approach... I'd seek first for bubbles and foam in the tank.

Hum, by the way, MIL-PRF-7808, 260F and low pressure. Jet engine, isn't it?

If the 2 stages have same configuration it will not help since cavitation occurs at ENTRY and has nothing to do with delivery pressure after the pump.

thank you all for your comments -

adding stuff to the system is painful, already have weight and envelope problems. We have tried to divert some of the high pressure pump discharge into the pump inlet but still have cavitation - perhaps need to divert more and sacrifice outlet flow performance (higher internal recirculation).

turbulence of the fluid in the tank (at 5 psia + inlet line loss) might add more air into the fluid but this is what happens - we did not splash the return fluid into the tank