I have a 22 gallon per minute PTO pump setup from a Case 1250 planter that I mounted on a Deere 1770NT to run the vac blowers and take some hydraulic load off the pulling tractor.  It's all plumbed up and operational.  Overkill capacity, but operational.   One problem:  at 1800 engine RPM, the pump acts like it starts sucking air.   The suction line from the reservoir starts to shake and the system surges.  Oil gets a little frothy too.  Under 1800 is no problem.  I have the reservoir almost entirely full -- way above the full mark on the dipstick.   It is about a 5 gallon reservoir.

I've taken the lid off the reservoir while it is running and it looks like a hydraulic oil tornado in there.   Do these things have a problem vortexing in the reservoir and sucking air down into the suction?  Or do I have another problem to look for?   Any ideas other than running throttled down or fabricating a bigger reservoir?   Do any of the Case planters run a bigger reservoir?

This seems like an odd problem to me as the entire system was unbolted from a brand new planter.  

Thanks for any ideas.