We are installing a "PTO wet kit" on our truck.

The kit, that I bought at a truck parts store, consists of a Muncie
PTO, 13 GPM gear pump, and a pressure relief valve with a cartridge
similar to Sun RPGC-LAN. I say "similar to" because the actual model
is a fixed pressure RPGC-L2500N, but it is hard to find anything in
google about that model number. RPGC-LAN is a number that is easier to
find.

I had a tank that I put to use.

Anyway, we did a first test of the system, with the output and return
hoses connected directly to each other. No problem.

Then we left the hoses disconnected, so that there was no circuit, and
proceeded to run the pump to test the relief valve at full pressure
and to warm up the oil quicker.

At first everything was great, pressure held at 2500 PSI, everything
was flowing. After a while, though, something happened and pressure
dropped to 500 psi, then more.

I started looking. The pump pumps with good flow, I know this because
I pumped some oil into a bucket.

Took out the pressure relief cartridge. I found out, to my surprise,
that it is very easy to puch the piston in with a plastic pen. If it
is a 2500 PSI valve, it should have taken a force of several hundred
pounds. Instead I can easily do it by hand.

The picture is he

http://www.sunhydraulics.com/model/RPGC

I do not really understand what could have happened and why this valve
could fail and become so easy to open.

Would anyone have any idea? What could it be?

Thanks

i

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