Pressure control valve problem

Warhorse · May 9, 2015

I have a 1975 John Deere backhoe 310. I'm having problems with the Pressure Control Valve. There is a nylon o-ring type washer that mounts in the valve.
The pressure control valve mounts to the side of the housing. I'm not getting much service before it blows out or whatever happens to it. I use
John Deere parts so, I'm not using anything cheaply made. I was wondering if anyone has had any experience with a problem of this nature. I haven't
been able to find any information on the technical side of things in relation to this. Thanks for any knowledge here.

Tx Jim · May 9, 2015

What is blowing out? Have you checked standby pressure? I think standby should be around 2250 psi

Warhorse · May 11, 2015

The o-ring in your schematic with the number 9 is the one blowing out every time. It's made out of nylon or plastic I think. I really don't know where to check the stand by pressure on this machine. I have a gauge and not sure if it will register that high or not. I know that is not normal for it to keep blowing it out so regular as it seems to now.
Sorry I didn't answer sooner.

Tx Jim · May 11, 2015

Are you replacing o-ring with the correct part number? Here are the o-rings spec's. You can check stand-by pressure at the frt pump. I'll guess stand-by should be around 2350-2400 psi. Have you checked to be sure pressure control valve isn't stuck in the housing or blocking flow?

Warhorse · May 11, 2015

If you are talking about the spring with the 2 little thin washers, yes, I checked it and it is free. I pulled it out of the housing. The housing has a small bleed hole in the end of the housing where the spring goes, very small bleed hole. I blew some compressed air through there and I can't tell if it is ok or not. I notice on the face of the housing, the side that has the O-rings, there is a small bb looking object that I pressed down on it and it didn't retract, and I don't know the function of it, maybe it doesn't work until pressure hits it. The front pump where you check the stand-by pressure; what fitting I check is a mystery to me, I just haven't done enough work on this area of a backhoe to know and trying to find someone who does know is seemingly difficult.

Tx Jim · May 11, 2015

You should be able to check stand-by pressure by removing plug(parts key 7) and attaching hyd gauge. I think BB you're referring to blocks(plugs) a passageway

Warhorse · May 11, 2015

Haven't checked the stand by pressure yet, but I did put a straight edge on the unit and using a flashlight I can see some light about the center of the unit. I'm not sure if that is enough to worry about unless under a lot of pressure it could be flexing enough to make it develop a leak. It's getting more and more complicated the further I investigate all
the possibilities of what's causing all this.