Fred,
This is one reason we have the hydraulic accumulator on the IV-P. It SHOULD absorb the slight volume change with temperature that causes the 2-seater hydraulic systems, without any buffer, to spike. Any chance your accumulator is “flat?” The test is operating your flaps (speed brakes?) with the hydraulic system power off. My flaps will do about 1 ½ cycles before the pressure goes to zero. If the accumulator has lost it’s pre-loaded pressure on the air side, the flaps won’t even operate through one cycle; probably won’t even extend fully? Bob
Accumulator is fine, Bob. But..... (there is always a but....) In addition to the normal hydraulic systems on the Lancair IV I also have hydraulic speed brakes operated by a cylinder mounted crosswise on the back of the main spar. The sum of all this volume causes more hydraulic fluid to expand on the same volume of compressed nitrogen in the accumulator increasing the thermal effect of fluid expansion. Note that I reported a change of only 250 psi from normal to hot soak. Without the accumulator it would have been much more. Recall that Chris Z said he saw a pressure rise to 2000 psi in his system with no accumulator.
The key question seems to be: what negative impact, if any, occurs from high pressure excursions in our planes? The first thing that comes to mind is o-ring extrusion in cylinders that leads to shortened lifetime. But is 2000 psi enough to extrude o-rings? Depends on cylinder to piston tolerances among other things. I don't know. Others may.
Fred