I need a little help here from a Hitachi excavator guru please. I just purchased the above referenced unit and got the ole girl home today. Checks out pretty good except for the engine control has been disconnected and the boom leaks down pretty fast. The main thing I am worried about is the boom leaking down. I thought it might be piston seals but wonder if both piston seals could be this bad as the boom still seems to work okay. When the boom leaks down it even leaks down enough to take the pressure of the machine kind of like the pilot valve is sticking a little or something like that. Does anyone have any suggestions for trouble shooting or perhaps know what could cause this? Any help is greatly appreciated!
Good day Alan Suggest you diagnose if the issue is with the boom cylinders or the valve's -rest the arm on the ground in the vertical position - stop the machine - disconnect the mail lines to the positive side of the boom cylinders and plug both ends with steel plugs - start the machine and fire the arm out so that the equipment rests on the cylinders, if it still creeps at the same speed your issue is in the cylinders - if it holds up the issue is with the valves. If you can answer it is with the valves come back and I will try to help some more. Kind regards Uffex
Uffex, Thank you for the information! That is a great idea. I will try your suggestion this weekend. Incidentally I did raise the front of the machine up using the boom and I do not believe it leaked down then but I wasn't really checking for leaking I was just making sure it had power. I would think if the piston seals leaked one way they would also leak the other way. What do you think?
Good day Alan It is less likely that the boom cylinders are guilty if the machine holds up the machine with the undercarriage raised but to be real certain I would carry out the test as described, in that way you can take out cylinders as suspect. The remaining possible components are lock and shock valve. I have attached a document that explains the problem and solutions, sorry its a bit heavy but if you can take the time to have a read it may well help. I will check the archives if I can follow up with individual details of your machine I will re-post. Kind regards Uffex
Hi again Alan I have checked the archive and I can only give you what I have, if you would post me a photo of the boom cylinder main lines and the main valve chest I can improve the information, I believe you have a KPM valve chest if you can find the tag and post that it would help. Kind regards Uffex
Uffex, This is great information! Thank you! I have a couple of pics available to me now. I will post them below but will take more. It is supposed to rain all day tomorrow but if I can get a break to get in there I will take more photos and post otherwise it will be Sunday. I am guessing the tag you need is on top of the main valve body. Thank you for all your help! Alan
Hi Alan Yes there should be a small tag there it will give the makers name - type - and some other info. A close up photo will be good enough. Keep smiling Uffex
Uffex, I could not test as you suggested due weather but I did raise the undercarriage up again and let it sit and it does not leak down. I let the engine idle so I could hear it better and I can hear the oil in the valve similar to when you are moving the boom on purpose. Also I noticed that while the boom is leaking down you can move the joystick to try and stop it from coming down and it will speed up a little when you first crack the pilot valve open then as you keep pulling the joystick it will stop then go back up as you continue. I can clearly hear the oil moving through the valve until the boom comes to rest on the ground. Pic of the pump tag below...
Good day Alan The tag on the MCV looks as if the machine was intended for the home market, not to worry its a little bit of a guess but from your text it would be sensible to take the shock valves out of the suspect list - these are adjacent to where you can hear the fluid passing. I have made some instructions if you have any questions you know where to find me. Good luck and let us know how you make out. Kind regards Uffex
I omitted to mention before you change the shock valves make sure that the equipment is rested on the ground, keep safe. KR Uffex
Uffex, Thank you so much! I will swap those two valves this weekend and let you know the result. Are those valves repairable? From your instructions it appears that if the shock valve is not the issue then it must be the lock valve. Is that valve located internally to the main control valve? How hard is it to change or repair? What is the difference between an MCV designed for the home market and one designed for other markets? Just wondering. Thank you for all your help! KR Alan
Good day Alan The shock valves are if the same we have experience are pressed together, it is possible to take the valve apart normally it is some debris blocking an office or lodging the piston open, I will check to see if I have a good illustration on file to give you. The lock valve is inside the block as to the best of my knowledge shall we face that one if it is the case as I believe it to be less likely. Home market machines are often to a different specification to that of those sold in the USA all of the text is in Japanese makes establishing parts origin a little more difficult. May post the illustration later. KR Uffex
Good day Alan Had some information but had to make it tidy please see attached. KR Uffex
Good day Uffex Thank you for the illustration. I see where the valve has some small areas that may be easy to plug up and hinder operation. I think this is the culprit. KR Alan
Good Day Uffex I finally got a chance yesterday to work on this machine. I purchased a new shock valve from an online source just in case mine was not repairable. The one from Deere was over a thousand bucks and the one I purchased online (from China) was $140.00. I hated to buy one without being sure but my time is limited so I wanted to have the parts there when I had a chance to work. Anyway I changed the valve out for the new one and it made no difference at all. So now I am not sure if I changed the correct shock valve or if the cheap one I put in is no good. I followed the lines from the piston side of the boom cylinders to where it ties into the valve and swapped out the shock valve directly above it. It appears the factory valve that I removed is serviceable but I only looked at it for a minute before moving on. It did appear to have some trash in it and also felt kind of sticky so I thought sure that was going to be the problem. Did I swap out the correct valve? Where is the place to go from here if the shock valve is not the problem?
Hi Alan I have used Chinese products before and my experience has on the whole been just as good as original parts, each shock valve has a dual function to 1 - relief over pressure and 2 - to permit back pressure to fill any voids caused by the displacement on the other side during relief. It is possible that this second part of the function is what has caused the issue - that being the case use that valve you have removed and switch it out with that on the opposite line. Please come back and let me know if it is fixed. Kind regards Uffex
Good day Alan Checking the notes I have on this issue it would appear that the cause of the problem is far more likely to the boom lock valve, I will try and dig out some information to help. KR Uffex
Good day Alan We believe this is how your M.C.V. looks if not give us a good photo of the Boom main valve, please see attached. Kind regards Uffex
Good Day Uffex Thank you for the quick reply. My M.C.V. varies slightly from the one you sent as mine has only one auxiliary and your's shows two. Attached is the best picture I have but I can take another if this doesn't give you what you need. I placed arrows showing the location of the shock valve that I changed. I will remove, clean and inspect the valve #18 as you suggest. It may be this weekend before I can work on it again. I will surely let you know the outcome. Thank you so much for the valuable assistance! Alan
Good Day Uffex, I have been studying my manual and I think my M.C.V. does not have the valve #18 at least not in the location shown on the diagram that you sent. I think that valve #18 is located in the position of the supply connection to the cylinder. Below are pics from my manual. E-E is the boom section according to the manual.
My dear, I have been already confused about this subject!!! HITACHI EX300LC-3 don't have BOOM LOCK VALVE!!!
By the way, how is the pump pressure at BOOM STROKE END (UP and DOWN STROKE END)??
Good day Alan Lachau informs us that the machine is without boom lock valve which is very unusual do either of you guys have the appropriate hydraulic schematic? Kind regards Uffex
That's true, Sir. Until Model EX300-5 has been just installed the BOOM ANTI-DRIFT LOCK VALVE!!
and....
Follows are attached Hydraulic Circuit Diagram of 2 model for your more convenience reference.
Good day Alan It would appear from Lachau's excellent information that your machine is devoid of boom lock valve, this will mean that holding the boom up is totally reliant on the valve spool which will leak allowing the boom to creep down. I would suggest the only solution is to install a after market boom lock valve, if you could source such a valve that may be sandwiched between the main hose and the M.C.V. the installation should not be to difficult. I would imagine that there must be out there given the volume of Hitachi machines that will need them especially as they become older and more worn. The only alternative's would be to fit hose rupture valves to both cylinders more complicated but common in europe which stipulates excavators must have them or you must live with the creep of the cylinders. Kind regards Uffex
Good day Alan This may help as an explanation KR Uffex
Good Day Uffex, I think the boom is leaking down too fast to be contributed to bypass around the spool. It will leak down from full height in about 15 seconds or so. I have been studying the manual but cannot find a reference to this part of the valve. Do you know what it does? Also I found this in the disassembly section where it refers to this valve as a check valve... Also I wonder if there could be something going on with the pilot circuit letting pressure leak into the boom lower spool. I noticed that I have to pull the control handle back pretty far just to get the boom to stop going down.
Lachau, Thank you for the explanation and the schematics and diagrams. Is there anything else that you know of in that circuit that could cause my problem?
Lachau, I have not checked the pump pressure as of yet.
Good day Alan The valve you refer is common to all spools prevent a back load running against the pump input it has no effect on holding up the boom sorry but that is how it is, if you can study the schematic that Lachau provided there is no boom lock valve provision for your machine I am also a little surprised most we have dealt with have such a valve. The fact you have to use so much lever movement could be an indication of spool and housing clearance, you could check the spring beneath the cap just to be sure its not broken or loose, this would only be the case if the issue suddenly manifested, a gradual deterioration indicates spool housing wear. Kind regards Uffex
Lachau, Looking at the cross section that you provided it shows number 11 is Load check valve for Boom 1 parallel passage. It appears to be in the same location as the valve in question in my above post. Could this be the problem? What happens if this valve is stuck open? Thank you for all your help!
Uffex, Sorry I posted the last question before I saw your answer above. I just bought this machine so it was this way from the beginning. I wondered if maybe the spool spring could be broken and causing this but could also be from spool clearance issue as you suggest. I will keep looking. Thank you for all your help!
Uffex, Do you know what this shut-off valve is for and where it is located on the machine?
Alan The symbol is that of a on-off valve I would assume it is the plug for a shock or overpressure valve which is not needed for your machine if it was open to tank it would slow the boom operation however you can see a check valve appears to be between the two mono block sections, this check was at fault it would be a combination of the two. I like your thinking Alan it is not impossible. KR Uffex
Uffex, Thank you for the information. Question. If the spool is the culprit for the leaking boom circuit would it not also leak down when the undercarriage is raised? When I raise the undercarriage it does not leak down.
Alan The spool housing is made up of chambers each is sealed by metal surface although one chamber is damaged it does not necessarily mean the other chamber is also damaged. KR Uffex
Uffex, Understood. Thank you for the explanation and illustration.
Oh, no!!! That is not correct!! You should check the opposite over-load relief valve which's located under control valve.
Hi Alan Yes the information is correct you have swapped our the wrong shock valve switch it with the one you removed and come back and let us know how you make out. KR Uffex
Hello Lachau, Yesterday I disassembled the top valve, cleaned it and reassembled. I then installed it into the bottom port and moved the bottom valve to the top. I did not find anything wrong with the valve I disassembled other than a small nick in the valve seat which I was able to repair. Moving the valves did not effect the issue. The boom still leaks down but will hold up the undercarriage without leaking down at all. I raised the boom all the way up with the stick vertical and it takes about 15 seconds for it to drift back to the ground. Also I raised the boom up then shifted the pilot lock valve to see if the drifting stopped and it did not. I was trying to eliminate the pilot circuit as the culprit. I can hear the oil flowing in the valve when the boom is drifting down. It is somewhat counter intuitive to me as to how the bottom valve would cause the boom to leak down since it is adjacent to the rod side port. Can you explain please sir? Thank you again for taking your time out to help me!
Alan, earlier you stated “It did appear to have some trash in it and also felt kind of sticky so I thought sure that was going to be the problem.“ what was the trash? 1 piece or lots? did u cut open filters and chk what’s in the hyd tank? I’d think if it has much you need to get it clean before trying to find the issue, as trash may screw up another valve while testing.
Jonno, There was a small piece of what looked like dirt on the small end of the valve. It may have gotten on there when I removed it as I did not see any trash or metallic particles when I later disassembled it. I am planning to drain and clean the hydraulic system before I begin using this machine but wanted to try to fix it first so I don't have to drain it again if I have to go deeper into the system such as removing the M.C.V. I have not cut open the filters or looked into the tank. I do have new filters but have not installed them yet. Thank you for the comment!
Is your spool centering? Did you remove the spool valve and inspect it and the bore?
LN, I have yet to remove the spool cover so I am not sure if it is centering or not. I think that may be my next step though. Are the bores normally repairable or does it require a new valve body?
In the past, I spoke with a machine shop that specializes in hydraulic equipment and repair about this. They claim that they can machine out the bore and install a sleeve. I don’t know how well this repair works. They did tell me that it is costly, and it is generally more economical to replace smaller valve blocks instead of do this repair. The shop that I spoke with was Spencer Fluid Power. I’d be interested in hearing first hand experience with such a repair from others if this is in fact your problem.
I guess you may have to disassemble the MCV!!! It's not serious but you have to separate MCV to inspect the check valve 01 as follow circuit!!
I think you should check this first before disassemble MCV.
Lachau, It appears that even if check valve 01 is not functioning the oil cannot get to the return due to plug 34. I am not quite sure of the purpose of check valve 01 at this point. I will remove the spool cover this weekend to check for centering and maybe damage. Thank you for taking time to share your knowledge with me!
Good day folks For plug 34 to be at fault would mean that the check valve 01 would need to have some issue, to dismantle the valve block would need either a vacuum pump or drain down the fluid.The check valve permits fluid from the boom secondary and not returning this could be to give better lowering control or and allow the boom secondary spool to be used for another function. Kind regards Uffex
Hi Ay, I mean the plug 34 is very...very...very easy to inspect; so You should inspect it before disassemble MCV!! Good luck.
Lachau, Understood. I will inspect it.
Hello, I was able to do some more trouble shooting this past weekend. I pulled plug 34 and the oring and back-up appeared to be in good shape. I was a little surprised as the oring was actually a flat seal similar to a piston seal but was not damaged at all. I am not sure it is sealed 100% but would be surprised if very much oil could leak by it and since my boom is leaking down pretty fast I think there has to be a pretty good leak. I pulled the spool covers and there did not appear to be anything suspicious such as a spool off center. I pulled the spools and they looked good also. I tried to feel around in the valve with my fingernail and could not feel any bad gouges or chips but I could not see in there as oil was coming out. I marked on the image below where I believe the possible leak paths could be. I could not feel any gaps in the shock valve seat so I think I have eliminated that one. It seems to me that it would take substantial gouges/damage to leak the amount of oil it takes for my boom to move as fast as it does. I really expected to see the spool maybe offset from center for this much oil to move but that was not the case. Also I wonder how oil gets to the rod side that fast but I guess that oil is supplied from the shock valve refill. I really would like to isolate the problem before I purchase another valve as they are quite expensive so any ideas on the next step will be appreciated. Also I am confused as to how oils gets from the neutral passage up the the cylinder port unless it is solely through the parallel passage.
It's all right, but you should check over-load relief carefully. It's a over-load valve with make-up function to suck oil from tank to prevent occurrence of cavitation in the circuit.
Could you take a photo of it??? I suspect that's not correct seal??!!
Lachau, I replaced the over load valve with a new one but a China version so I was suspicious that maybe it was not good. I then disassembled the existing valve cleaned it and installed it into the bottom of the MCV and put the one from the bottom into the top and it made no difference. I also swapped it with the one next to it (arm I think) just to make sure again. I checked the valve seat the best that I could with my finger nail and did not feel any gaps. The seat on the existing valve did have a small area where it appears a piece of trash went through it but I was able to repair it. I thought the seat may also be damaged but could not find any damage by feel. I had an idea to replace the overload valve with a plug (34) just as a test to completely rule out the overload valve and that circuit but I found that the plug straight across from the valve would not fit. I guess I should have paid more attention to the cross section as it is obvious that it will not work. Plug 34 appears to be good. It did not have an oring as I expected but a square cross section ring with a back-up. I wondered if it was once round and just flattened out due to age. Do you know if it is supposed to be a round cross section? I haven't removed the valve from the machine as of yet so I cannot inspect the check valve between the two housings. The next thing I want to do is use a leak down tester to try and isolate the source of the leak.
It is so good idea, man.
Quick update: I finally go some time to work on this thing and ever indication was the MCV was bad. I replaced it and now everything is good. It wasn't easy or fun, especially for a non-mechanic, but I got it done. All hydraulics are functioning properly now. I replaced the pressure switches since I had it apart and also replaced the speed sensor. Now all the electronics seems to be functioning properly also so maybe was a good investment for a farm machine. The chains are worn out but I think if I remove a link they will be fine. I have never taken out a link. Can anyone offer any "tricks of the trade"?
Good day Alan See attached I hope you find it helpful. Kind regards Uffex
Thank you Uffex! You are a wealth of knowledge and your presentations are second to none!
Thank you for your kind remarks this may help also. Kind regards Uffex