So, as the title says, slow bucket dump , somewhat random, sometimes better when cold. All other functions normal and correct time. Owner had some guy fix it but this owner never gives us the whole story, and its now back to doing it. We have checked all pressure switches and sensors, all good. Anything come to mind with you experts? thanks in advance.
Bound up pin bushing Bent linkage Bent rod Nut loose on rod allowing piston to bind in tube
Not an obstruction in the line causing low flow?
Good day Suggest work from the cylinder - check for by-pass of fluid - make sure that the spool is full shifting - test pressure on the dumping line compare with the opposing direction that should show up a leaking shock valve in addition to those suggestions made. Kind regards Uffex
Full model number and a serial number is necessary. Have you checked the basics yet? Any visible damage to the cylinder? Have you pulled the return filter looking for plastic material or steel? How many hours on this machine? Any leakage on the cylinder? Any fault codes on the monitor panel?
A fast and easy check, is switch your pilot lines on the control valve. (Opening/closing), if the problem is on the opening side then, remove and check spool valve, if no changes, then problem is your cylinder.
All mechanical things have been checked, it is narrowed down to the spool or pilot. Its like it doesnt send enough pressure randomly to stroke the spool. The owner is one of those impatient guys that you never get the whole story from, then when we have time to work on it he "needs it" and we cant get far on it. So he can deal with it. If we do get time to solve it I will post.
So we were able to get back to this issue. PC250LC-6LE A83030 The dealer cannot find a parts diagram of this main valve that has the correct o-rings even. Entire machine work great except bucket dump is slow. All the obvious basics have been covered To clarify, my coworker and myself have 40+ years each working on equipment, mostly JD. Spool has been removed and is free in bore, valves in that circuit are newish and clean, no metal or scarring. Pilot pressure , modulates up to 500. Here is the testing, Dig is curl up, dump is curl out. Hanging with a bucket on, dig takes 1900 psi measured at pump to start moving,dump 2900. Dan switched hoses at the boom. dig ,1000 to start moving, dump 4400 Installed test blocks at boom hoses, dump motion, 2000 psi back pressure when it should be near zero, dig no back pressure as it should be. Wrong spool? in upside down? And what the hell is the two pistons on the bottom of the spool in the housing, looks like some sort of limiter/ modulator, and these are now dumping to tank to make sure spool full strokes. Thanks Russ
The A serial number means the machine was made for here. The dealer should have no problem getting info from the factory on that machine. Have you opened up the cylinder to see what is inside? Does this machine have a three way return on the bucket circuit? Do you have a photo of the where the two pistons are installed? I've seen lots of issues with the boom and stick before. Never seen your type of problem with the bucket circuit.
Its not the cylinder. other " mechanics" needlessly had it rebuilt.. What is under the long cover between the work ports? Schematic looks like double check valves. John, you in portland by chance?
I'm between Tacoma and Seattle. I'll get into my old books later today. In those years Komatsu was constantly changing whole valves and control circuits so I'll see what I have that might cover your machine.
That would be great, Im thinking we should have just removed the modulator pistons from it while in there. This machine is going to finish its life in a quarry so no need for grading feathering.LOL We have a service manual but its pretty worthless. And im not good enough with hydraulic schematics to decipher operation.
Your serial number info shows the machine to be a 1997 model so you likely have the possibility of lots of other issues as well. Does the bucket function change when you operate other things as well? Try swinging at the same time, traveling at the same time or boom and stick together with the bucket at the same time and let us know what happens. The book I have covers early 8000 serial number machines but I think it should be close enough. The two valves or spools on the outlet end are sub unloaders and I don't think have anything to do with your problem. In looking at the schematic, it appears that one of the compensator valves on the bucket function is leaking sensing oil thru and preventing the opposite compensator from opening. The pressure compensators are just load check valves that have signal oil coming from all the other functions which apply the same hydraulic pressure to hold the check valve closed as that other function is at. It's done to allow multiple functions with different operating pressures to operate all at the same time. Say you are operating the boom up and the bucket close at the same time, boom up pressure might be 2,000 PSI while the bucket could be closing at 3,500 PSI. The load check would have the 2,000 PSI holding it closed until main pressure on that function was able to equalize pressure. If that function wasn't there, the bucket close function would operate at the same 2,000 PSI as the boom. The pressure compensators can be resealed but the big rub is recognizing when there is enough wear on the components of the valve that new seals would not help. When the first problems started happening back in the day, the dealer just replaced all the compensators on all the individual valves. That was expensive and involved replacing all the hydraulic oil as well. Were it me, I would pull those two compensators out and tear them down to inspect and go from there.
We have done all the multi functions, bucket never changes. The dealer did exactly what you are saying, changed all the compensators, I do not know why. I am told this problem was new. The compensators we pulled look new still. No wear or scratches, no debris. I studied the schematic and still dont see why it would have back pressure on the backside of cylinder in dump function, doesnt the spool just dump to "tank" cavity during this? Thanks.
What doesn't make sense is that it only happens on the bucket circuit. It's the last function on that valve and that oil should all go back to the cooler, return filter and then the tank. The schematic did show the return going through something else before it got back to the return side of the spool. I'll do some more studying and get back.
I've looked again and the only thing that strikes me is that maybe the bucket spool got flipped end for end. You might try popping it out and flipping it over and see what happens.
It has the modulator pistons on the bottom, I personally didnt see it, can they be put on the other end of the spool. What about the shuttle check valves between the work ports.?
I'm not sure of what you are calling modulator pistons. The load sense system doesn't need any modulators to make everything work smoothly. The check valves are LS checks and they are part of the load sense system as far as I know.
There are 2 "rings" on the bottom of the spool, they are inside a longer than normal pilot housing . I have no idea what they are called, I think I sent pics earlier.
Those are spacers put in to center the spool in the correct relation to the ports in the valve body. My book doesn't show them specifically but the pictorial schematic does show that side of the spool being on the bucket open side of the valve body. My book shows the end with the extra body should be on the top side of the valve body. There are a couple of little balls on the inside of the valve spool as well. When you had the spool out, did you check that those were there and not stuck to one side or the other?
These spacers and housing are definately on the bottom I did not, my co worker was working on it. What are these I assume, double checks for? I really appreciate your help with this
I believe those are the LS check valves. These machines are closed center load sensing. What that means is that the spools are always closed off to the pump flow and the pumps are set up to only put out a little bit of flow when all the spools are centered. Oil comes out of the pumps and into the valve bodies and the flows down the center of the valves which when nothing is being used stops flowing at that point. There is a second passage that goes to the LS circuits for all those functions. One of the functions of that LS circuit is to tell the pumps to destroke and not put out any more than minimum flow. Those checks are part of that LS function. Your pumps are stroking up when something is used so I figured that there was nothing wrong with those check valves.
Did you say you have a service manual for this machine?
I think, ill check with Dan my coworker. We were wondering if the spool is upside down also. And the dealer is NO help, and they worked on it. They just want to sell a valve. Not happening on a machine of this age. Our thing is if the valve isnt cracked in half ,we can fix it.
Dan said the engine is loaded all the time. Anyway his next step is to pull those on that block and inspect them. Ill let you know what we find. Again thanks.
Here is a photo of the valve block. Item number 6 is the bucket spool. This diagram has three extra spools that you might not have on your machine. The book photo is sideways so if you rotate to the left you will see the actual representation of the valve as it sits in the machine.
The trouble shooting chart is pointing us to the suction and suction safety valves, but our book doesnt call them out. Thanks
In English those are called circuit relief valves and they wouldn't have anything to do with restricting the flow into or out of the circuit. They only relieve high pressure or prevent a vacuum in the circuit.
Ok, that makes sense. This is a very strange issue. Check balls in spool are ok, LS checks under the cover I sent a pic of are ok. We can flip the spool over unless we move the pilot housings also because of those pistons on the spool. Seriously thinking about taking them off the spool and trying that.
I'd flip the spool and sway the housings as well. It wouldn't be the first time I've seen someone put a valve back together and get the spools in the wrong holes plus in the wrong direction.
It appears we have found and solved the problem. I dont know if Dan took pics , but unscrewed the spool ends to check the check balls and they were there, on one of the stems there was a machined groove that looked like it accepted an oring and backup. So he put one on it, before reinstalling the bucket spool he pulled the arm spool and took it apart, sure enough the groove had a seal on it. Assembled the valve, oiled it up and lo and behold the bucket works like it should and it doesnt load the engine as much as it used to. We suspect the seal was for a sensing port of some type and causing the loading and back pressure. John, thank you for everything.
Ive seen this problem many times with hydraulics, and after so many costly troubleshooting procedures, I have found what generally causes it is a bad hydraulic hose.... when we get a machine in that has the symptoms, after the pressures all check out good, we go directly to looking for a bad hose.... sometimes its just a failed seal somewhere in the system. on hoses, when the fittings are installed, if they get over crimped, the hose liner will be damaged and a "flap" can develop on the inside of the hose at the end of the fitting on the inside, creating a flapper valve.... when it gets big enough it causes a restriction and sometimes it can cause a complete blockage, but the function always works smooth and proper in one direction, but in the other direction it can be either erratically or fail dependably..... and about the only way to find it is to systematically swap the hydraulic hoses in that circuit end for end, one at a time and test running it before swapping the next hose.... the other issue we sometimes find when this happens (usually on pilot operated valves), is the spool valve is sticking, due to a spool that has came loose and is unscrewing itself inside (depending on the design), a broken spring/adjustment came loose or a bit of contamination that is not letting it travel full in one direction.... there is little else that can cause the issue...
centerline, everything you described was not the issue. Its the first things we checked, we have over 40 years each in this business. It was a part left out by the dealer as it turns out.