Mysterious cylinder config, please help identify

[mwhalen]

I disassembled the check valve assembly and all seemed well. The only thing I wondered about is the poppet rear has a gap where a o-ring looks like it may have gone, but isn't there:

Although, the press is able to go from quick advance to slow as expected. If that needed an o-ring, the worst that could happen (I would think) is that it wouldn't be able to quick advance. It would be able to achieve the high force requirements, it would just take longer to get there.

This makes me think even more that the problem is with the cylinder itself. How about my pressure relief valve swaps with the solenoid valves? Wouldn't you agree that I ruled them out by doing that? Who wants to bet against me when I say it must be the cylinder?

edit (add): should mention that there was no hole in the poppet (I might be naming it wrong, maybe it is called the shuttle and the poppet is on the other side). The other side has the conical pieces that actually seal off flow. One of those had holes, but they were quite large and clear.

 

[wdchyd]

You're probably right about seals in cyl, they are prone to more wear and tear than the valves.....

the valve you show in your hand I believe shouldn't have an oring...It's tolerance fit in the housing....it looks like the piston that unseats the check valve on the other side to open main cyl to tank...No?....

Can you us a jack or porto-power to induce a load from the table pumping it up while the Press Ram is extended and the power to the press is off.....This will show integrity of the pistons seals.....Maybe your assumtions are correct whereas the press doesn't go up to pressure not because the press can't deliver but rather the cyl seals are by-passing.....if the pressure holds tonnage with the jack/porto-power then your cyl seals are likely not your problem.....

 

[wdchyd]

The small hole in a poppet scenario would be in a relief valve (pilot operated)....then it would not come up to pressure and the poppet would open prematurly (the tiny hole allows pressure in to hold poppet on seat to build pressure.....

I think that valve you have is a pilot operated check valve .....

Was that Hyd schematic one that came with the press or one you drew up?....I didn't see that valve on there the way it was drawn......

 

[mwhalen]

I drew it up. Pretty much all the other parts had info either on them or available online using part numbers. Nothing on the cylinder assembly had any info so I didn't do more than sort of scale draw that on the drawing.

 

[mwhalen]

the valve you show in your hand I believe shouldn't have an oring...It's tolerance fit in the housing....it looks like the piston that unseats the check valve on the other side to open main cyl to tank...No?....

Yes, you are right about that.

Can you us a jack or porto-power to induce a load from the table pumping it up while the Press Ram is extended and the power to the press is off.....This will show integrity of the pistons seals.....Maybe your assumtions are correct whereas the press doesn't go up to pressure not because the press can't deliver but rather the cyl seals are by-passing.....if the pressure holds tonnage with the jack/porto-power then your cyl seals are likely not your problem.....

That makes sense. I think we have a suitable jack. I may give that a go on Monday, God willing. Thanks.

 

[mwhalen]

We began to suspect the check valve that is integrated into the machine and so we plugged it's port to tank to see if it was letting our high pressure go to tank. When plugged, we were able to achieve the required pressure:cool2:

Here is the shematic now with some refinement including the pilot operated check valve drawn in:

From the way I understand it, the check valve, which I'll call BV1 (bum valve 1) should only be opening up during retract? Do these illustrations make sense:

 

[wdchyd]

Mwhalen,

Looks like you're getting there....

Re: BV1......usually POCV will open with pilot pressure on retract to dump and will open thru suction on quick advance (for make up oil).....either way it should hold pressure when de-energized.....

I've seen other units that will open with pilot pressure both directions using a shuttle valve to isolate oil from each side.....sometimes the shuttle valve is bad and bypassing to wrong side of piston......

Did the press come up to pressure on it's own or with external load induced?

 

[wdchyd]

Can you get to the poppet in the POCV....maybe the poppet has a wear spot and the seat is worn.......

I've had luck regrinding poppet, indicated in lathe and ground with tool post grinder the proper angle ......after grinding use a fine lapping compound to lap the seat with the poppet.......

Before you do that inspect the seat carefully for gouges or chunks or something abnormal.....

 

[mwhalen]

Took the check valve apart again to see and found the spring that should keep the thing seated was broken. I definitely should have noticed this when taking it apart the first time, but didn't dig that deep. Now the press functions normally as before. However, our gage lab hasn't signed off on it because the press spikes up to 30,000lbs and works down to our setpoint (~14,000lbs). They demand that this spike be removed. I'm fairly confident that this is the way it has always worked. Do you suppose I could be right?

 

[wdchyd]

Normal operation should not do this....it could be a problem with SV1 spiking when spool is shifting during the transition......where is the pressure guage plumbed?.....maybe you are reading pressure not at the ram but just ahead of pump before the SV1?......maybe use your load cell to verify if spike is at the ram....then maybe PRV1 is not venting properly or a bad seat/burr internally....

Direct acting relief valves relieve themselves quicker than Pilot operated RV's so this machine may have been doing this all along......