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Does anyone know what this valve is and how it works? Looks like a pressure relief. Can it be adjusted in any way? Where might it be placed in the hyd system?

Yes looks like a pressure relief valve for a hyd system and yes most can be adjusted

(quoted from post at 15:44:41 12/18/11)
Does anyone know what this valve is and how it works? Looks like a pressure relief. Can it be adjusted in any way? Where might it be placed in the hyd system?

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It is definately a pressure relief valve, very similar to what we used for a low pressure safety on our test machine reservoirs. I don't know what pressure your's is, but we used a very low pressure version adjustable from about 4 or 5# up to 20#. We set these reservoir safeties at slightly over 15# and adjusted the pressure with an air regulator... the relief valve was just a safety pop-off if the regulator failed. Plumbed the "tank" port to drain into the sump if it happened to pop off.
The top "cap" covers a screw adjustment and the nut is a lock-nut for the setting.

I will be putting this on an old "M" 1944 with the weaker cam gear. Adding an M+W live hyd pump.

If anyone knows a good way to set this thing so hopefully I don't break my gear I'd love to hear....

And still a good place in the line to place this and work correctly to save that gear..

A friend of mine just busted his cam gear and we are in the process of fixing it, what a fun job.

Its adjustable, remove acorn nut on the end and see a set screw. loosen lock nut and screw the screw in or out to increase or decrease spring pressure. To install put a tee into the pressure line from the pump to control valve. Install relief valve in the tee and run tank port to a no pressure opening on the reservoir. To adjust plumb in a pressure gage, back out the adjustment screw on the relief valve. Dead head the control valve momentarily and see what the pressure builds to before relief valve opens. If its working correct it should build less than 800 pounds. If it goes to 1000 or 1200 without relief poping with adjusting screw backed out a ways stop and check the valve. If it works like it should you can adjust screw in a little at a time and keep checking the PSI until it gets to what you want.
Wouldn't go over a 1000 PSI and if it would do what you want with less PSI, 800 or 900 would be better. M&W used a relief valve just like that one in some of there systems, mostly set at 1000 PSI.

The "press' side just "tees" into the pressure side and the "tank" side just goes back to the reservoir.

What is funny is that Greesen STILL makes a valve just about like these to this day!


like everyone is telling you, DO NOT get above 1000 PSI.Can be trouble.

If you need MORE detail on these.E mail me.

I should have explained that these come in several pressure ranges... the ones we used were the lowest range available, but some were made to go to probably go to 2500 or 3000 psi. The range should be stamped on it somewhere. These are direct acting (as opposed to pilot controlled) and can be "noisy" when relieving at the set pressure, and are also somewhat variable with the flow. A pilot operated Rv will remain the same no matter how much flow is going through it when relieving, up to the rated flow.
I would back the adjustment off and plumb the pressure port directly off the pump pressure port with no other components in the system other than a guage between the pump and Rv, and the tank port back to your reservoir. This way, you know exactly where it's set and that flow isn't going somewhere else in a system. I don't know how much pressure your cam gear or the M&W pump will take, someone with that experience will need to give you that advise. The way we used that type of valve was not really the intended purpose, but they did the job... we never blew up a reservoir with one of these on it. We started using them after an air regulator stuck and blew the top off of one of our reservoirs... it happened over night when no one was in the department, but people in other parts of the plant heard it.

Thanks to everyone's knowledge on this site. It is amazing there are some many people willing to help with this stuff.