hydraulic problem

This topic contains 35 replies and was last updated by richard-bettler 9 years 11 months ago
November 25th, 2011 3:49pm
Need help on a hydraulic ram that is not working. when the ram is connected to the hydraulics, the bucket pulls in and locks - won't release and stays pinned until hydraulic lines are disconnected. Ram was recently bent and subsequently replaced. After replacement, the "lock jaw" effect occurs. Any help would be great.
November 25th, 2011 10:54pm
The cylinder is dumb and can only do what the oil directs it to.

Can you tell what you feel at the hoses? Does the hose flowing the oil flex hard and remain hard while the cylinder is pinned, as you call it?

If the hose remains hard and inflexible, it tells me that the spool valve is directing the oil there and maintaining the pressure in the cylinder.

If the hose relaxes, but the companion hose does not pressurize to release or move the cylinder in the opposite, again the problem is in the spool.

It is possible the event that bent the cylinder rod, created a hydraulic surge that damaged or broke the spool valve. Be very careful: that kind of pressures can have also severely damaged the hoses and they will likely fail unexpectedly.
November 26th, 2011 6:07pm
Your answers are GREATLY appreciated. What I've found is that the replacement RAM is fine - hooked it to another st of hoses and control is good from there. Of the hoses that were connected, with engine on, the side that is "pinning" the bucket/ram is constantly pumping fluid. Whereas the other side just "dribbles". so I suspect you're correct that the problem is in the spool valve. Now, FINDING the spool valve might be a bit of a problem. This is a mini excavator, ditch witch model mx-15 and from what I can follow, the valve must be under the cab. All other hydraulics seems to work flawlessly, so I'm assuming each hydraulic supply line pair have their own spool valve?

thanks again for the advice.
November 27th, 2011 1:35am
I am gratified that you are finding your way through you problem. However, I do recommend that you inform your boss that you want to take some training on hydraulics. Hydraulics can be extremely dangerous to the guys who try to learn on the job. There is a lot of theory that must be absorbed.

At the very least, spend time reading, and one place I do recommend, is this site:


There is a treasure trove of information. Take advantage of it.
December 1st, 2011 7:14pm
I will do as adviced. One additional side effect that appears to be happening is that, now that the cylinder and ram are not functioning properly, the ditch witch has trouble starting. Would hydraulics hold any influence on the engine?
December 2nd, 2011 4:09pm
Hydraulic systems that have constant horsepower type pumps and controls have the ability to change the way the hydraulic system runs while working but should not have any effect on starting. Units this small is not likely to be equipped with this anyway.

What do you mean by hard starting? Does it crank and not start? Does it fail to crank? Is there something like a Murphy system that needs a button pushed? When you crank, do you see the oil pressure come up?
December 7th, 2011 2:09am
I just wanted to provide some insight on one of the previou threads that stated that a constant horsepower hyd. pump, such as pumps used on excavators, do not cause starting problems. Actually they can have a drastic effect on starting. I spent the last couple of weeks diagnosing a crank-but no start condition on a Cat 312 CL excavator. After thoroughly checking every possible cause on the engine and not finding the cause, I decided to measure my pump discharge psi while cranking. My left pump discharge psi while cranking was 2000psi! This is an enormous hydraulic load that acts as a parasitic load on the engine, which reduced my cranking rpm to about 250-320rpm which was not enough to start. My diagnosis led me to a spool that was stuck in my auxillary control valve section. This excavator used a negative flow control (NFC) type pump regulator system. When the joystick is in neutral, NFC signal pressure is high and signals the pump to destroke. In my case, the stuck spool routed my NFC signal to tank, reducing my NFC pressure and signaled the pump to upstroke which resulted in 2000psi of load on the engine when cranking. It sounds like you're on the right track but keep in mind that parasitic loads, such as loaded hydraulic pumps, can have a considerable effect on starting. I suggest determining what kind of hydraulic signaling or pump control system you have and measuring pump discharge psi and signal psi while cranking. Be safe, hydraulic fluid injected into you can be fatal.
December 8th, 2011 4:33am
electronexciter: of course you're right. I didn't think of the problem in that vein. But as you indicated in your problem, it loaded up the starter and slowed down the cranking. A very good response. Thank you.
December 9th, 2011 2:51am
Jimo, who would have thought that a hydraulic problem could affect engine starting? I was tearing my hair out after working on this machine for weeks and not coming up with anything! It wasn't until our Tech Support Dept. recommended testing for hydraulic load while cranking, that I started to catch on to the root cause of this problem. This project was an interesting learning experience.
December 9th, 2011 11:28am
Had the same thing, worked for 2 days on a frozen grader, thinking...this can't be right! Alas, one of the functions was loaded.
December 11th, 2011 8:30pm
Well, I guess we still have to wait and see if [email protected] has found and corrected the problem.

And I hope [email protected] will come back and tell us what he did find. We are all waiting with baited breath.
December 27th, 2011 7:05am
My appologies for not returning to the thread in a timely manner. I have been in search of a mechanics manual for this particular little machine so that I can track down the mentioned stuck valve.

All indication is that you are correct that the load of the hydraulics is pulling down the starting. Currently, the machine will not start at all and you can smell the heat coming off the starter as it strains to carry the load. I'm afraid the starter may have suffered some damage from the problem and excessive load.

I'm up for any clue on how I can track down a manual for this beast - have had no luck as of yet with the dealership - or if there is a way to release the pressure so that we can start the system to be able to check other components. Currently, we are simply tearing the machine down in blind search of the stuck valve in question without a manual.
December 27th, 2011 11:16am
Hi what type of machine do you have.DO you have still a problem with starting?
December 27th, 2011 6:16pm
It is a Ditch Witch MX-15, basically a Komatsu mini-excavator that Ditch Witch re-labeled and sold under their brand. Yes, I've not solved the problems on the beastie yet. I do believe the earlier posts are on track with my problem, but without the mechanic's manual, I'm stuck just blindly disassembling and searching for the valve causing the problem.
December 27th, 2011 7:13pm
Ok ..can I get information about your problem again?Is there problem with ram or starting?

I working for Cat dealer and maybe I can help.
December 27th, 2011 7:27pm
Ok..can I get information about your problem again?Is there problem with ram or hard starting?
December 27th, 2011 7:35pm
What we seem to be suffering is a stuck control valve on the bucket. the bucket's hydraulic RAM locks out fully extended and won't retract. As a result of the over-pressure, the mini excavator won't start at this point and the excessive load has caused the starter to over heat (proably will require replacement of the starter). The big problem is that I haven't a clue where to find this control valve and have no manual for the machine. I've contacted a ditch witch dealership and have had no success acquiring a mechanic's manual, which leaves me digging blind for a part that I've never seen. This eveil little machine was part of a business acquisition that we picked up and now I'm stuck trying to correct it's problems.

any help would be great.
December 27th, 2011 7:48pm
I think that control valve (for small excavator for example cat) should be under floor but there is problem with identification without manual.does machine have pilot controled control valve.You can watch hoses (high pressure)from cylinder (ram) to control valve and find correct spool.May be you can check pilot lines from control (joystick) to control valve.the joystick can have leaking and one send wrong control pressure to main control valve.

I am sorry for my englih.. :-)
December 28th, 2011 4:53am
Your english is fine. Tested the control stick by swapping the functions with other hoses. Definitely under the floor somewhere. Although I believe I have finally begged hard enough that the dealership is emailing me a mechanic's manual. THAT would be a godsend.
December 28th, 2011 9:07am
The manual is good thing.I have one question:Does the cylinder move itself after starting of engine?If yes I have a same experience:contamination or spool.The spools are centering one or two springs.The spring are connected to spool by bolt.The bolt sometimes is released and one moves spool from centered position and open port for function.

Did you have damaged cylinder?If yes there is contamination from cylinder in lines(hoses).

The main control should be near control for travel.You must remove rubber carpet(under legs) and cover for access to main vale.
December 29th, 2011 2:51am
THAT sounds spot on. We had the bucket's RAM bend and immediately lost fluid, which probably brought in contamination. I will see about changing the oil and filter and locating this spool. When you had it occur, were you able to clean the spool and get it working or did it require replacement?
December 29th, 2011 9:06am
Ooou...Did you replace or repair ram??The ram could create steel particles (may be rubber particles from seal) which could come to the control valve and stuck(hack) the spool.You need to disassembly control valve (may be remove the group of control valves-hard way) and clean it and flush the hoses.When you will folow hoses from ram you can find the control valve with out manual and you can try disassembly the control valve on the machine (drain oil from hydraulic tank).

My customer worked with hydraulic hammer and one has retracted cylinder into end position.The energy from hammer cames to the piston of cylinder and damged piston and cylinder and created lot of steel particles which cames to the control valve :-(
December 29th, 2011 9:27am
I am sorry I forgot..on you question about cleaning or replacing control valve.

Replace is depend on the ammount of contamination and damaged.

My recommendation:

1 step:disassemble control valve(on the machine if is it possible)-remove spool and relief valve and use the pressurised air to clear.THe oil going to out can remove the contamination too.The spool should go to out by hand

2 step:assembly it and connect hoses..disconect hoses from ram and insert hoses to the container(barrel).Use function for clear (flush)the hoses.

I hope that this help you..
December 31st, 2011 7:52pm
did u ever resolve the hyd issue?
January 1st, 2012 5:55pm
Hi,Yes I do.I am solving electric and hydraulic problem..Why? :)
January 6th, 2012 3:21am
My appologies for the tardy response times. We have a lot going on and the mini excavator we can only spare time for sporadically. It is indeed the spool that seems to be the problem from what we can tell. It does not slide evenly and looks like it might be ever so slightly bent - how that could have happened escapes me. Right now, our biggest concern is that the manufacturer does not offer a replacement part for the spool or apparently the valve. I'm hopefull that I might be able to find a machine shop that can fabricate a replacement spool. But where that is concerned, I'm also open to suggestions. Is there such a thing as a generic spool valve that I might be able to replace the unit outright?
January 6th, 2012 5:25am
Definitely do not consider trying to replace the spool only when it seems that it has been bent and worked in the hole. These things are built to 10,000ths clearances, a metal to metal clearance to withstand maybe 5,000 PSI. It is sure to be scored and internally damaged and will certainly cause leakage.

I think you had better look harder with the manufacturers rather than local parts dept. They may simply not stock something, and then tell you it is not available. That machine is built by a respectable manufacturer. I think the part can be found.

As for replacement with a generic valve, yes, it is possible. There is no magic to these valves. But cheaper valves may not have the life expectancy or be able to control the pressures as well because of clearance issues, plus you are likely to have linkage problems.

You must prove whether it is open centre or closed centre system, and has the pressure and flow capacity required.
January 6th, 2012 7:58am
Jimo is right,

lot of valves are not serviced and you can replace only group (valve not only spool :-(...)

I think tha you have open center system because some mini excavator (small class)are using gear pump (my experience), large class are using LS system.

Can you check whether main control has identification plate?It may help to you find correct parts.

Did you find something in the valve.(contamination or damaged?)

Did you disassembly valve or did you try only move the spool?

If you find identification plate can you provide pictures of plate to me?May can I help you
January 7th, 2012 3:41am
We had the spool checked at a machine shop and it appears my eyes need checked, since spool spins level and straight. Having said that, we buffed the spool a bit and returned it to the casing, still meeting resistance. Blowing air through the system has not resulted in an additional debris, but in frustration, we got a bit medieval on the thing and just worked it angrily in and out of the sleeve. Low and behold, we finally churned up the ccntamination and broke the resistance free. Spool moves smooth as butter now. I'll let you know once we get the mess reassembled if that was the fix.
January 9th, 2012 4:29pm
We also have a Ditch Witch MX15 and I have been unable to get a Service Manual. Any chance I could get that email with the service manual forwarded?
January 10th, 2012 3:16am
It seems you still don't get it. The metal to metal clearance might be 5 ten-thousandths between the spool and the housing. Your getting MEDIEVAL and chopping up a bit of o-ring, well you may have gotten away with it. But if the blockage was a chunk of metal or a burr, well guess what it did to the clearance.

Learning by experience is not a very good way to learn.
June 24th, 2013 9:18am
"Learning by experience is not a very good way to learn." I'm flattered by the quote you said. Thanks a million to Mr. Jimo for his precious advice on Hydraulic ram problems. I have been in this pickle for one month and fortunately I came to this forum today and found the solution from a very noble man. Thanks a lot.


WQSeals LLC for Hydraulic Cylinder Seal Kit is the choice of all industrialists
June 25th, 2013 3:07am
Check out these plugs to prevent losing any hydraulic fluid... Tight seal and have always worked great.
June 25th, 2013 3:10am
I would check out these plugs while the lines are disconnected. You shouldn't lose a drop of hydraulic fluid in the process. They worked great for me.
June 25th, 2013 3:12am
I would check out these plugs while the lines are disconnected. You shouldn't lose a drop of hydraulic fluid in the process. They worked great for me, and I have actually used the same standard size on a few different projects. www.serviceplugs.com

July 3rd, 2013 9:16am
well !! i just wana shre this !!

its about an OLSS hydraulic system s we say !! (open center load sensing systems)

i have a problem on one of our excavator !! komatso !! maybee japanes design !!

the controls was somkind of fitted with a Jet valve !! its like an orifice itself !! converts flow into pressure so the more the volume of flow the higher the pressure !! then the signal pass to the displacment control i think !!

also problem with stock spool !! thats why the engine seems like being hold back or just shut off !! also hard to start !! engine is stalling !! the problem is with the hydraulics !!

i found it out !! when i read an article on this site !! www.insanehydraulics.com !!

well im just self studying !! for now the excavaot is running good !! after resolving the problem !!

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