GLP050PGNUAE086 Forks creep down a few inches after lowering them. Dosent do it when raising forks. Dosent seem like the valve either. Also lifting power is lower than it used to be. What should the relief pressure be when lifting?
Showing items 1 - 17 of 17 results.
One other thing I noticed. On the control valve there is a pressure relief valve on the outlet housing next to the side shift portion of the valve. Is that for the side shift or is it a second relief valve? Someone welded the adjustment on it so its non adjustable now.
If the packing or the valve on the bottom of the rod are faulty there will be a staging issue, not a capacity issue.
First verify with a known weight that the unit can't lift it's capacity with the hoist cyl. If it can't, try lifting the weight with the tilt back function. This will test the hoist portion of your hydraulic valve. If it will neither hoist or tilt it's rated capacity, then pressure checks before & after the control valve will be needed to find the culprit- either a faulty hyd pump or faulty control valve.
This is the complaint from the operator. It cant lift as much as it used to. So if the cylinder piston seal is shot, the lifting power of that cylinder is reduced from the area of the bore diameter to the area of the rod diameter.....or did I understand that Wiki explanation wrong? I should probly do all three cylinders along with the steering cylinder that leaks too.
You say a lack of lifting power- what do you mean? What are the symptoms?
Ok that sounds like something I was suspecting but I still have a lack of lifting power @ 3300 psi. Maybe I need a new gauge.
Forklift- I learned this type of cyl the hard way. Worked on a hoist cyl on a newer clark which I thought only had packing at the bottom of the rod. Imagine my surprise when upon disassembly I found 2 sets of packing- at the top of the barrel & at the bottom of the rod. I had quoted a simple repacking (the rod was severely scratched & I wound up rechroming the rod). After I lost the customer because he was **** at the rechroming charge- I did alot of research on what the cyl was & how it worked. The simplest explanation is at http://en dot wikipedia dot org/wiki/Hydraulic_cylinder. Hope that helps
BB, I have never read the theory of operation on these style cylinders so send me a copy if able. To me, a "displacement cylinder" , even back to the old 355 tall triple cylinders, works on the principal that you put a quart of oil in, you get a quart of upward movement. Same for a lot of other lift cylinders that don't have a piston or a check valve.
Forklift- why do you believe these style cylinders are not true "differential"? The theory of operation is that oil, which is top of the bottom packing (by design), goes thru the valve on the bottom of the ram when the rod begins to move upward, mixing with the incoming oil, increasing pressure & volume under the ram allowing the ram to move faster & have more pressure behind it than is supplied from the hyd. pump.
The upper gland nut on these type cylinders has packing installed, not just a wiper.
Well Ed, unpack your bags and take off that tropical print shirt and sandals.
forklift is correct, had I known about the staging issue, I would not have suggested the fuse at all,,, repack the center lift cylinder complete, not just the gland nut.
Ah. Easy. Reseal the primary lift cylinder. You are gonna find either the piston seal is crumbling or the small check valve in the center of the piston has trash in it. I suggest to always pull the snap ring when resealing this type cylinder to replace the outer small oring as they sometimes fail. Anytime you have these style cylinders (they are not a true displacement style, and nobody seems to know the name of them) and the secondaries begin lifting before the primary has staged all of the way up, it indicates that oil is gotten above the piston seal. You can usually force the mast all the way up once empty and this corrects the staging for a short while till the oil gets past the piston again.
i did try the manual valve. it reacts the same. if i remember right, these cylinders have some sort of check valve in the bottom of the rod. im not sure of the hydraulic theory on the three cylinder system but this one will raise the twins with a load before the center cylinder goes up. i have not seen that happen before. the relief pressure is about 3300 psi.
I would install a manual shut off valve in the feed line. Make sure the valve is open & raise the forks, then close the valve & check for creep.
If creep disappears, you have a control valve issue. If it's still present, then a cyl issue is your cause.
At that point, if a cyl issue is present, then install shut off valves to the secondary cyls (if present), raise the forks again (no need to raise high enough to engage the secondary channel) & then shut off one cyl at time to check leakage of that cyl. If creep is still present after testing both secondary cyl's, the primary cyl needs service.
Even if it's just the "hydraulic fuse" as Ed stated, I'd remove the cyl & have it serviced by a hyd shop for safety's sake.
FFT mast? A bypassing secondary lift cylinder can do this- and it's the cheapest repair. I suggest removing the snap ring or bolt fastening the right secondary rod to the mast, lifting mast all the way up, chain the intermediate lower cross bar to the outer channel top crossbar. Careful! Lower the carriage to the bottom of the inner channel, then let the right secondary cylinder drop all of the way down and now you are able to test/ prove or each cylinder one at a time. I don't remember if you are dealing with JIC fittings, but what you want to do is remove the supply line to the right lift cylinder and plug line. Extend mast all the way again, remove chain and test for mentioned dropping down. It will operate fine with only one secondary cylinder doing the work. Reassemble and REPEAT on the left side. This test will allow you to isolate the defective cylinder and confirm needed repair. We do this process often. Again, be careful. YOUR SAFETY IS NOT MY RESPONSIBILITY
this may well be (sounds to me) what I call the "velocity fuse" in the lift cylinder hydraulic circuit.
Forklifts (when new and repaired as designed) have a device that is designed as a 1 time use/non-reset-able hydraulic fuse, that is designed to prevent a 'guillotine' effect of the carriage falling like greased lightening should the primary lift feed hydraulic hose break between the mast and the valve. it doesn't prevent oil leaking or the carriage coming down **** quick, just not as quick as without that fuse. when 'blown' the fuse does not prevent lifting, it just limits flow when lowering, you may be seeing the effect of that limiting factor. In thins truck, I think they call it a lowering control valve and it looks like a fitting into the tee that has the hose from the control valve, (and that is the hose the valve attaches to) and hoses that go to the lift cylinders, but this lift cylinders also look to have a fitting-spring and washer setup in the bottom of the lift cylinders that may also be part of your problem and worth checking by pulling the fitting out of the bottom of the lift cylinders to see if it may be malfunctioning..
I am soooo very tempted to say this, but I would NEVER EVER say this...
the best way to know, and maybe the only way to ever get this unit to run right again would be to fly -me- to your neighbourhood to look at it, for a week, maybe sometime in January...
But I would never say that... [and besides, Stam would need it more than me... what with him living in the 'great white north' and all].
;-)
what makes you think it isn't a valve? i do not have spec's for your truck but a typical 5000lb truck is at 2500-2850 psi. if you are low on relief pressure it isnt always the pump at fault. investing in the service manual for your truck might be a good idea. hydraulic components can get very expensive.
Forkliftaction accepts no responsibility for forum content and requires forum participants to adhere to our rules of conduct. Click here for more information.
If you are having trouble using the Discussion Forums, please contact us for help.