Mysterious cylinder config, please help identify

[mwhalen]

Hi,

This is a picture of a press cylinder. I do not understand what the components are at the back of the cylinder. We do not have schematics for the press or part numbers on the cylinder/cylinder assembly. I'm trying to put together a drawing of the system. If anybody can shed some light on this I'd be grateful.

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. I just don't know exactly how this one works.

 

[wdchyd]

Mwhalen,

That's another cyl piggybacked to give the press high speed to come up quick to your load without wasting time.......

Once the main cyl contacts your load then high pressure kicks in for tonnage....

They do this for the quick retract and extend instead of using multistage pumps......

Some manufacturers use microswitches for adjustment of stroke and some use pressure switches

 

[tglass]

may be the cyl.,but something tells me it's not. interested in the cause of the problem and like to see your findings and how you discovered what it was though. not any help, but is very interesting.

 

[wdchyd]

The block with the large hose and hyd tubing between the cyls, is a pilot-operated check valve that opens with a hyd signal for the fast fill (when going down) and opens for fast dump to tank when going back up.....

Hope this helps.....a hyd schematic would be helpfull also.......:thumbsup:

 

[wdchyd]

I like the "Sanitizing" job on the pics......nice CNC's in the background:thumbsup:

 

[mwhalen]

That helps. Thanks. I knew there was some kind of hi speed lo speed going on because sv2 is labeled "quick advance", yet it helps to know how that configuration achieves that.

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?

 

[mwhalen]

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?

 

[wdchyd]

Cyl seals could be your culprit as an internal by-pass will not be evident visually......

The air bubbles are air entrainment from a suction leak (suction hose, fitting, tube, or hyd pump shaft seal)......don't really think lack of pressure is the air bubbles unless they have compromised the pump or relief valves.....

One way to find suction leak is let it sit overnight to clear oil in tank......
then use #2 grease to cover over suspected places one at a time.....leave cover off reservoir tank and start up for a few seconds.....if still bubbles then move to the next suspect....and so on......

My initial suspect would be the shaft seal on the pump, it will draw in air when running....use the grease and glob on the exposed seal on pump......(hopefully exposed)if it's the shaft seal you might hear it smooth out under start up........either way the only place it'll draw in air is on the suction side of the pump.......if the leak is on the pressure side of the pump it'll leak out......

 

[wdchyd]

another thought on this is use an infrared non-contact thermometer to possibly scan out a bad PRV or check valve....even bad piston seal in cyl may show as a temp rise......(although the cyl barrel is pretty thick).....

Also the PO check valve between the two cyls connected to reservoir, did it have a piston poppet and bias spring internally.....some poppets have a teeneetiny hole in them, make sure it's clear.......

Hope this helps.....

 

[mwhalen]

I'll have to disassemble and check that out. I appreciate your input. Thanks!