Hydraulic valves

Anonymous Poster · Jun 28, 2000

I have a John Deere 790 with the rear hydraulic remote. For those not familiar with this setup, JD takes the power beyond tap (normally goes to rock shaft) off the SCV and creates a loop to the rear of the tractor with a hose and quick disconnect. If you are not using the rear remote, you must have the hose connected in the quick disconnect to complete the loop to the rock shaft and back to the tranny. They tell you not to operate with the loop not connected or through an open center valve. My question is - does the valve need to be just open center or must it have power beyond. I have asked locally and no one seems to know, even JD dealer. From what I see, the power beyond is not needed if I do not want to operate the remote and rock shaft at the same time. Also, there is not a provision for a return line to the transmission is the JD setup, thus having the open center return to the transmission (as with the SCV) means some fancy plumbing. I do know that if I have the open center return to the transmission instead of the rock shaft, I definitely need power beyond.

Thanks for any input.

MChalkley · Jun 28, 2000

Halsey - The valve only needs to be open center. This allows the fluid to dump to tank when it's not being used, which keeps from burning the pump up. The only reason you need a power beyond port is to power additional hydraulics through valves which must also, by the way, be open center.

The thing you can't do, whether the power comes from a power beyond port or not, is dead-end the power at a quick-connect. It has to go back to tank. So, what's usually done is to run the power through an open center valve, and dead-end the outputs from the valve with quick-connects.

I hope this answers the question you were asking. Hydraulics can be as messy intellectually as they are physically.

Mark

gordon · Jun 28, 2000

Can anyone tell me what a rock shaft is and whats it for?
One more question whats a SCV as well? Thanks in advance.
Gordon

<P ID="edit"><FONT SIZE=-1>Edited by gordon on 6/28/00 08:12 PM.</FONT></P>

Anonymous Poster · Jun 29, 2000

Gordon - the rock shaft is the term for the shaft that the upper arms of the 3 point hitch are attached to and "SCV" is selective control valve - the valves that direct the flow of hydraulic fluid to cyclinders or whatever is attached.