Re: Back pressure valve on 600 hydraulic lift.

The backpressure valve on the 600 lift cover is located behind the check valve assembly. To access it, you'll need to remove the "pipe plug" from the front of the cover directly underneath the seat. Grab the first thing you see in there with a pair of pliers by the boss, and it (spring holder/plug), the check valve spring, and the check ball will come out.

For the next part, you'll need to have a 3/8-24 x 6" or so threaded rod, nut and a washer. You'll need this to pull the check valve ball seat. (I'm sure you'll figure it out.) Good luck on not breaking it - you'll need it! (BTW, if you do break it, FNH thinks a lot of it, to the tune of $95.)

What's left behind that is your backpressure valve assembly. It's just a spring and spool; no o-ring.

Good luck. I don't know if that's your problem, but at least you can get at it now.

Here is a stab at posting a picture of the high pressure relief valve.

The itty bitty pieces at the top right are all that is left of the springs

I think I'll remember to check the load if something similar happens to me. An after the fact diagnostic might have been to close the flow control valve and give the 3ph some load shocks.

From what I understand, there is no shock load protection in neutral on a 600. But then, 600's have been around awhile, so I guess the design works just fine.

My friend who owns the tractor just happened to have a shop manual for the later 4000 tractor with SOS and it did have a picture of the back pressure valve and the check valve in exploded view alony with the procedure to remove the back pressure seat etc.

It was OK.

I finally decided to try to figure out how to take out the high-pressure relief valve since I had already taken the unloading valve apart 3 times.

(Reminded me of the good old days when I had to do this stuff!)

When I got it out and removed the set screw that the book says not to remove under penalty of death and discovered that the outer spring was in about 10 pieces. Undoubtedly this is going to be the problem. I am going to the machine supply place on Monday and try to find a spring to fix it with. If it only holds half as much pressure as it is originally supposed to it will be more than twice as much as it has now and I don't intend to spend my gold bars on a new one.