Hello everyone! I am new to this site and have not been able to find a thread with the same issue I am having. I purchased an old ex county single axle International 4700 dump truck with a Heil 1715 dump body on it. When I lift the bed I have to raise the rpms to get the bed moving. When I move the raise lever to the hold position the bed will drift down until it full closes and I can’t get it to stay partially raised. I started throwing parts at it by first re-sealing the hydraulic cylinder. That was pretty straight forward however this cylinder was unlike any I have worked on in the past. It has an internal bypass poppet valve. From what I can tell it allows oil to flow through a small orifice to the other side of the gland as you are raising the dump bed and extending the cylinder. When the cylinder reaches full stroke a spacer hits the end of the cylinder cap and pushes against the end of the “poppet” and closes it. I may have a misunderstanding of how this works but I think that is right. One I re-sealed the cylinder the bed was still drifting. I went ahead and installed a new open center Cross spool valve since it was almost as cost effective as replacing the relief valve and resealing the old one. The new valve came with a new relief valve and all I had to do was install it on the truck. Well to my surprise the dump bed still drifts. A few other things to note are in the process of changing out the spool valve I noticed the hydraulic pto driven pump was leaking so I went ahead and put a seal kit in it. I also capped off the line to the hydraulic cylinder and installed a pressure gauge to see if the pump was making enough pressure. It made it to about 2500psi before it stalled the truck out and killed the engine. Has anyone had experience with anything like this in the past? I’m wondering if the cylinder could still be the problem and somehow that internal bypass poppet valve is not working properly. It seems like if it would let too much oil by when lifting the bed it would make it difficult to raise and then would allow the bed to drift as the oil wasn’t staying on just one side of the gland. I have attached a break down of the cylinder and parts list. Thanks in advance for any help or recommendations! I can still use the truck but I would like to fix this issue so I can tailgate material more efficiently.
Ball and spool prevents oil from passing through the piston during normal operation. The device aids in air removal in the barrel side of the cylinder and lessons over pressurization, both when the cylinder is at full stroke.
heymccall Thank you for your reply and for the info. Even though this is the correct break down of my cylinder when I took mine apart instead of a ball and spool it had a tapered cone which I think is the same? I have included some photos. What doesn’t make sense is it looks like the pressure from the bore side of the cylinder pushes the cone open and would allow fluid to pass to the rod side. When I raise the bed and the cylinder reaches full stroke I can keep it raised as long as I leave the lever in the raise position. I hear a high pitched whine when it reaches full stroke almost like a relief valve but it is coming from the cylinder. I also noticed in the parts breakdown it shows that there should be a plug with a bleeder valve in it in the cylinder. Mine is just a plug but I think that is ok too as you can just loosen the plug to bleed the air in the system. Would you happen to have any recommendations on additional ways to troubleshoot this?
By open center you are referring for use with a constant displacement pump aka gear pump I've witnessed people refer to a motor spool as open center witch is incorrect. But that was a argument from a few moons ago with the engineer aka the boss man.
Tyler Yes that is correct. My PTO has a drive shaft that powers a gear pump. The pressure side of the gear pump is plumbed into an open center spool valve. I believe that is the correct valve to be in place rather than a closed center spool valve ?
Yes it should be correct
I Suppose you could put a ball valve at the cylinder use a rope or stick to safely isolate the cylinder when raised to prove it good or bad
Jonas302 thanks for the input! I’m planning on doing that as now mysteriously the bed stays raised with a very slow leak down after a few hours with no load in it. Once it’s loaded it leaks down very quickly. I’m thinking I could have damaged a seal when installing or my new check valve might be faulty.
My workstar international 7400 dump bed leaks down when unloaded too. I can visibly see it go down. Would this be an issue with the electronic hydraulic valve? I don’t see leaks anywhere