Had a guy ask me to put a hydraulic pump on his lull high reach forklift. Said he has the pump off already and a new one there. Problem is the first pump he says split the case so he put a new one on and fired it up and that pump split also. Im guessing the first thing i should do is back main relief off before starting. Anything else i should do?
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Lull hydraulic pump
- Thread starter Moonlite
- Start date
BillG
Senior Member
You didn't give any specifics such as model and serial so I don't know what you have. That said the first place to start is to check plumbing. I don't know if you have an open or closed center hydraulic system but if it is just a standard type gear pump it would probably be open center. If someone has placed the pump main line on the wrong port it could be blocked and the relief valve wouldn't be in the circuit.
willie59
Administrator
Better do your homework Moonlite. I have little experience in troubleshooting Lull hydraulic systems, but I do know, and again, the model has a lot to do with this, that Lull typically used gear pumps with a closed center hydraulic system using various "unloader" type valves to maintain "standby" pressure along with accumulators. They are a very complex system, way more than a simple "back off the main relief valve". The fact that it busted two pumps indicates the standby pressure is way too high. Just what's causing that is what you're gonna have to figure out. If you are going to take on the job I suggest you get the hydraulic schematic for the machine and study it real good as to what could cause that to happen.
willie59
Administrator
Finally made it to the machine today. It is breaking the housing on second stage pump. From what i read in manual this supplies fluid via the steering priority valve.
Customer gave me a run down of events. They lifted a full constuction dumpster and moved if about 75 yrds. Cut unit off. Went back to restart fluid running out. Replaced pump idled unit everything was ok then tried to raise boom and oil started running out. Broke housing again so replaced again. All was fine until they tried to drive it. Busted housing again. I pulled return and pressure filters and didnt find anything that jumped out at me.
Customer gave me a run down of events. They lifted a full constuction dumpster and moved if about 75 yrds. Cut unit off. Went back to restart fluid running out. Replaced pump idled unit everything was ok then tried to raise boom and oil started running out. Broke housing again so replaced again. All was fine until they tried to drive it. Busted housing again. I pulled return and pressure filters and didnt find anything that jumped out at me.
willie59
Administrator
That's a starting point. I've been looking over a diagram, not certain I'm looking at the correct one, but there's a lot of gizmo's in a control valve after oil leaves the pump. Messed up o-rings on those cartridges could do some strange things, I'd pull every cartridge and fitting out of that control valve and replace all the o-rings and back up rings. I just know that most Lulls of that vintage used positive displacement pumps and various valves to control the pressure, both working pressure, pilot pressure, and stand by pressure. If anything goes haywire with those various valves, that pump is going to continue to do what it does...displace oil. If the path is blocked, and relief is faulty, boom.
Thanks willie. Checked on seal kits to reseal hydraulic manifold and control valves. Jlg said couldnt get complete seal kits as some seals have been discontinued. I dont feel real comfortable about just trying to match them up. So they are going to reseach farther and see what my options are. Not ordering parts yet just trying to give customer a heads up .
tractormech
Senior Member
If it split two pumps and it has the large blue block in the middle of the machine [control manifold system] then the compensator seals are blown or the valve is bad. Usually the steering is very hard and the machine will sound like it is laboring just sitting there running and not doing any function.....be warned...it will split pumps as fast as you put them on like it is now. The compensator valve is located in the front of the blue block and has a short hose hooked to a steel return line going back to the tank. The blue block is marked with a "CS" for the valve location. You need the model and serial number to verify this info and get the correct seal kit. They are expensive...the last one I bought was almost 200.00 just for the 1 valve but I did not want to take the risk of buying the wrong type or hardness seals....too much liability. Good luck!
Equipment Rental
New Member
Hey I am having an issue with a lull 6k-37 same blue block system. It has 10gpm flow at idle and getting 0 psi to the pilot test port and no functions are working. I removed the compensator valve and replaced the o-rings it had all incorrect o-rings on it. It is not splitting the pump but fully bypassing all the fluid and they owner has already been working on this machine so I am not sure what all he has messed up. The filter had all the sealing springs and attaching pieces removed and the filter was just tossed into the basket and was not doing anything. Do you have any suggestions?
DMiller
Senior Member
RUN!!!
Equipment Rental
New Member
HAHA!!!! I WOULD IF I COULD. I THINK I GOT SOMETHING. TURNS OUT THERE ARE MORE TEST PORTS ON THIS THING. PUMP 1 SHOWS 0 PSI PUMP 2 SHOWS 2000 PSI
tractormech
Senior Member
There should be a pilot directional valve and a pressure reducing valve in the block as I remember-if the o-rings are blown you won't have pilot pressure and therefore no function. Do you hear a bunch of noise -loud hissing and does the block feel like it's getting hot? Also a serial number might help
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tractormech
Senior Member
Just to clarify-you have no hydraulic functions at all...no steering,no boom functions...nothing? Are there any buzzers going off? And,will it go in gear or not?
LOL....Best reply yet!
Equipment Rental
New Member
Serial is AUG95X12N15-110 it has no functions including no steering it will go in gears but park brake does not release. Talked to JLG they said these are notorious for the compensator valve going out and blowing the pump up so they said since I have 0 psi on pump 1 to order the pump and compensator. There are no hissing noises or leaks.
tractormech
Senior Member
If I were you I'd pull the pump and have it checked before I went and spent 2k on a new one.I'd ask the history on the machine problem-has it been slowly going down hill or did it happen all at once. If the owner has been working on it himself he may have cranked down on relief valves or something before you started working on it so that would need to be put back to correct specs. You have a can of worms there and it can get ugly real quick.There's a lot of unknowns going behind somebody. Pump one may not show pressure until a function is operated so if the pilot system is inoperative then it will stay at 0 psi. Take the line off the pressure side of pump 1 and turn the engine over and see if it's moving oil out-that'll let you know that the shaft is not stripped.