<<From: Randy <randystuart
Then
the pump pressurizes the high side and it stops, and the shuttle valve centers,...>>
This is where pumps in the fleet differ. In my two pumps the shuttle valve does not return to center. It stays where the fluid last pushed it. The O-ring on the spool offers up much more friction than the spring on the poppet valve could ever hope to overcome. I am curious if all pump vintages have O-rings on the spool valve and/or how snug the fit might be? If the spool can be made to stay put, the problem goes away. I am simply suggesting this as something to investigate before a lot of new plumbing is added to the system.
A little over a year ago, when
this issue was last discussed, I took a series of photos showing the effect of heating and cooling. What is observed is that the high side pressure goes up and down with temperature (heat gun and ice bath) while the low side remains at zero.
My pumps are '95 and newer.
Chris Zavatson
N91CZ
360std