pressure switches

Back in November when I finished my gear system I bought a good pressure guage to measure pressures on both high and low side. I found that the hi side pressure at pump turnoff was about 1125 psi and on the low side it ended up at 850 psi. These are somewhat higher than specified in the manual. Attempting to adjust them lower, I followed the procedure of turning both screws CCwise in small increments each time cycling the gear to measure pressure. I could not achieve a noticable reduction in the pressures at which the pump turned off (maybe 25-50 psi); but adjusting the screws made large changes in the declining pressure set point; i.e., the pressure at which the pump would cycle back on when the pressure was slowly bled off.

During these measurements I also determined that about 200 psi (at the cylinders) would raise the gear and less than 300 psi would fully retract the gear; close the nose gear doors, and hold the gear firmly in place. Also, as the gear is running up, the pressure drop in the lines is over 400 psi, so including the drop, it appears that it takes 700 or more to retract the gear. Interesting, but I digress.

I just wanted the pump to turn off at the settings no higher than the 1000 and 500 given in the manual. The Velocity folks couldn't give me any answers; seems that I'm the only one who has ever measured these things. They referred me to Value Engineering Products (VEP) who makes the switches. VEP suggested that the switches had been tampered with (adjusting screws turned out of balance) and that I could return them to be recalibrated. So one day I took the switches off and sent them to VEP.

A few weeks later they called me and said the switches were ready, please send $45.00. Huh? Anyway, I got my switches, reinstalled them and; guess what - no change! Their calibration test showed the lo switch opening at 550; but in my system the low side pressure after the pump turns off is 850; high side still around 1100; and adjustment makes little difference.

I don't like excessive pressures in there (and I certainly don't like the 2000 psi Jean Prudhomme and others have noted after flying around awhile) but I decided to forget about it..., the system works fine (and I only have very little fluid seepage at those O-rings that don't have a proper seat).

However; I discussed this again with the manager at VEP (like maybe I should get my $45 back?), and now he also would like to understand what's going on. Has anyone else measured this pressure overshoot, particularly the lo side? And is it just inertia in the pump, delay in the relays...what??