I just bought a 40H and I don't have drive or lift and the swing is very slow. It is a standard control machine with the LSG423 engine and vickers proportional valves. I checked voltages at the proportional coils and they have good voltage and are pulling strong. There are 2 valves that are called dump valves in the parts book and someone marked them with a PV on the machine at some point. One of them is small with#4 lines going to it and is mounted just aft of the proportional valve on the right side support for the ground control box. That doesn't seem like it has big enough lines. The other valve is mounted just above the pump forward of the engine on the left side of the turret. The pressure line from the pump runs into that valve and there are 2 other lines connected to it. All three lines are large. I would assume that is the actual dump valve? The coil on that one is cracked open. None of the wiring prints in the service manual seem to exactly match this machine. Any help anyone can lend would be appreciated. The service manual is not really helpful with where things are located. I'm starting to get a feel for the JLG wiring prints but they leave a bit to be desired also. Thanks in advance.
My understanding is the dump valve is normally open when no input is desired. When you give the machine input, it closes to build pressure. I assume this is so they can maintain pressure without running the pump against the relief valve all the time. I am working on a 45HA. I have an issue with the drive not getting to the 3000 psi in both directions. one direction it will get to 3K, but the other only gets 2400 psi. I tried shimming the pressure relief on the valve, but no luck. I was looking at the dump valve maybe not closing all the way. The schematics are frustrating.
I relate to the frustration. I'm an aircraft mechanic by trade so thought this would be a simple fix but the jig schematics and manuals leave a lot to be desired. The guy I got my lift from told me it was working fine last fall when he parked it but had no drive or lift this spring when he started it up. Everything seems to check out electrically at least from the ground controls but I get no operation from the lift or drive but slow operation on the swing. I'm thinking I may have low hydraulic pressure from either a dump valve or relief valve stuck open. I think I finally have the right hydraulic coupling to check the pressure and see what's going on when I get back home from visiting family for the holiday.
Well, take a good look at the hydraulic schematic. Theses machines, if similar to mine, has a 3 section pump. The dump valve only is connected to the one section for drive and lift functions, check to see if the other functions work. There should be a test port for the valve block. I looked for the seal kit for my dump valve, and they don't make it anymore, just the complete valve. But I don't think that is really my issue. It sounds like you might be looking at the valve or the pump.
After looking at it again, it seems the dump valve is directly connected to the foot pedal. It looks like that is the emergency dump if your foot comes off the pedal. Do you not have any controls from the pedestal or the ground control panel? The schematic show when you switch it to ground control, it activates the dump valve as well.
I have finally had success with my lift!!!! There was a small piece of metal stuck in the proportional relief valve holding it open and dumping almost all the pressure. When I actuated the proportional dump valve I would build about 150psi which was enough for a very slow swing but nothing else. Once I got that taken care I lost platform controls which turned out to be some moisture in the ground control box. Enough to bleed off platform control voltage but not enough to pop the breaker. Just need to order a new starter switch for the platform as it has a very high resistance and we should be good. It's going to be really good to have around the farm. I did suprise myself though with how fast it drives with the engine switch on high and the high drive switch turned on. The next step is new oil and spark plugs along with some KANO Kreen treatment for the gas and oil and we should be all set to work. Mike
This sounds like the area where I'll be searching soon.... intermittent drive and boom fault. Feel like I have a head start now cheers Lads....