Why not a hydraulics forum?

[Micah]

We've got hydraulics in all our CNC equip where I work. Also, I have other equip that has hydraulics, but can't be categorized into any other forum (press). Why not have a forum dedicated to hydraulic equipment?

I'll even get us started:

Problem summary:

We seem to be getting full system pressure, but the press cannot achieve above 2200 pounds on the load cell (verified independently); should get up to 8k+ lbs. I believe I've ruled out most of the other circuit components and am very suspicious of the cylinder. Here's a pic:




I put together a drawing of the circuit:



What has been tried so far:
PRV1 (proportional pressure relief valve) was replaced with a solenoid valve to rule out the possibility of too much relieving going on. No difference.
VRV1 (variable [manually] relief valve) was replaced for the same reason. No fix.
The unlabeled flow control/check valve was taken apart and inspected and found to be in fine condition. It does adjust the quick advance portion of the press as expected, but there was some question of its check function being defeated possibly. Yet, we're not sure how that would affect the system and it doesn't appear to be likely from how it is physically made.

We are able to get 3000psi system pressure. Other same application presses (different manufacturer and config) are able to press with pressures of ~1800psi.
We currently haven't got a clue as to part numbers and specs on the cylinder and its piggy back check valve.

What started all this was a periodic cal on the load cell prompted a replacement request on the load cell. The press was working. Within hours of the calibration of the new cell, the press stopped being able to fully achieve stroke. It needs 8000 pound of force to achieve stroke on one part to give you and idea. It can only achieve 2200 right now.

What do you think is the most likely cause(s)?
What verification steps can we do to be sure before wasting a bunch of time and money on the wrong parts?

edit (more info):

I did notice that the tank has lots of bubbles in it when the pump is running. I know aeration is a bad thing, but how to tie it to any particular component? Is it really a smoking gun?

[bsharp]

Hello
Did you ever get this problem sorted out? Normally bubbles "aeration" in a hydraulic system is caused by cavitation "pulling a vacuum". It is not on the schematic but is there a suction strainer on the pump inlet that may be clogged?

[Micah]

yes, it was a check valve integrated into the cylinder assembly that was dumping pressure to tank during the high pressure phase of the press. There was a broken spring in the check valve.

[juice01]

Hi All/
I agree with micah. A hydraulic forum(press) would be a great addition to this site.
Cheers