Hydraulic jack testing

[Paul001]

We have built a jig to test hydraulic jacks. Under extend, we put the jack under 2400psi pressure. The pump is turned off and the pressure drops to 2000psi. We lose a little hydraulic fluid.
When we retract the jack, we pump to 1200psi. When turned off the pressure remains at 1200psi.
Is the jack damaged? Is it the internal seal that may have dirt or rust that causes it not to seat properly when extending?
Any advice is appreciated.

 

[Compositepro]

Perhaps the relief valve in the pump leaks a little at 2400 PSI and not at 1200 psi.

 

[hydtools]

Without a check valve to prevent backflow to the pump, any resulting backflow will reduce pressure.

Ted

 

[Paul001]

Thanks