Hello i am working on a hitachi ex 4oo lc-3, it blew up a hydraulic pump so we replaced it, then we took it to the job site and it ran fine, up until it started to raise the boom slowly on its own without being controlled, if anyone could help plz comment below! thx for looking!!
Chances are you have a stuck main spool.
Debris from the bad pump is likely causing a stuck spool. Did you clean the system out when you put the new pump on?
yes flushed it throughly, and checked the spools dont think they are hung up, was working fine for like a half a day then started raising the boom on its own, also when the saftey lever is up the boom still continues to go up...thx for your help!
Spool fo boom is stuck, remove it and see what's hanging it up.
fo? 4 spool side or 5 spool side?
you will need to pull both spools. the boom circuit has #1 and a #2 spool witch is on both sides, Pull the bottom caps also you might find contamination there. This will also help flush out anything in there when the oil drains through. Be careful not to get wet. Also when you have the boom spools out clean them up and make sure your counterbalance valve in he spool is still free moving( since you have it out). Just shake the boom spool and you will hear it slide back and forth inside. In the past in have had to do a lot of cleaning and removing to clear up problems. Good luck.
Dr. Dc what is the purpose of the counterbalance valve, and if it is not free what problems does it cause?
when booming down I helps retard the cylinders so it will not run away on you and hit the ground hard. sometimes when they get stuck in just the right position they will cause the boom to raise very slowly. This is just a check I do when there is contamination in the control valve especially if the spool is already out.
Thanks for the reply. I have an EX200LC-1 that has the problem of letting the boom go down just as I pull back on the joystick to lift the boom. As the stick is pulled back further then the boom will go up. It's sort of like a dead spot where the boom will "float". In your opinion could the counterbalance valve be the problem? Also, if it is the problem, how much of a job is it to fix? So far I have eliminated the joystick as being the problem because I just changed it from Cat controls to John Deere and the problem is still the same. Thanks for any and all help you provide.
Ok have you checked the valve body under cab it has a fine mesh screen on one fitting to catch any debris in line ,also 2 more on valve body behind spool in that control valve
No I haven't. The only valve body between the spool valve and the joystick is the one which appears to control the automatic engine speed control. Is that the one you are speaking of?
The boom circuit has a load check valve in the control valve for both the boom 1 and boom 2 spools. Its purpose is to prevent boom drift when you begin to input a boom raise input on the control lever. If you have the boom in the air then there's say 15 Mpa of pressure in the bottom of the boom cylinder. When you start to begin boom raise and the boom spools open, the pump pressure will be gradually rising. The load check valve prevents the 15 Mpa in the cylinder leaking off causing the boom to drop until the pump pressure equalizes with the cylinder pressure. The check valve seat will probably be worn or have debri holding them open. You'll need to remove them to check. Problem being if you haven't got a technical manual then they'll be difficult to find.
Thanks for the reply. I have since had the problem fixed, and it was exactly what you said it was. I had the complete spool valve rebuilt. The good news is that all it cost me was parts. My best bud from school is the head instructor of the heavy duty mechanics course at a local university here and he took it on for me. There is a poppet valve inside the hydraulic circuit that holds pressure as you stated above. Once I was able to get my hands on a repair manual I traced out the problem. If anyone else has the same problem there is an easy way to test if the poppet valve is the problem. The hydraulic circuit will also block the pressure when the travel circuit is put into operation. Therefore if you make the machine travel and then lift the boom, you'll find that it works as intended. Once you stop travelling you'll be back to the same problem again. Apparently this is a common problem with these old machines. Anyway, thanks for the input. I'm a happy camper now!
Hello CSWalker, I am experiencing similar problem with a Fiat HItachi FH220. When I lift boom it is oK, but when I lower it, I can't controll its speed and goes down too fast. what do you think it could be? best regards,