The Importance Of Knowledge - Failure Analysis From The Seat

Chris Diagnostician Lansdale, Pennsylvania Posted   Latest   Edited  
Case Study
Heavy Duty
Education
Unable To Hydraulically Couple Implement
Overheating Of Hydraulic System
Hydraulic Breaker Incorrect Operation

Hydraulic systems, and their schematics, may very well account for more puzzled individuals than even electrical systems.

The subject of this case study is a John Deere 30G compact-excavator (essentially the same machine as a Hitachi ZX30U-5) which came in with a complaint of customer having a difficult time hooking and un-hooking hydraulic lines for auxiliary attachments; in this case switching between the hydraulic thumb and a HH40C hydraulic hammer (aka breaker). I will run through the initial steps taken and then delve into system operational characteristics from there. 

The first step was to verify the complaint and so the lines for the hydraulic thumb were disconnected and re-connected with no issue. The lines for the hammer had excessive pressure build up and so the couplers were loosened and the oil pressure slowly bled off. The machine was then switched into 1 way flow mode per implement installation and removal procedures. The lines would then couple properly and un-couple properly. Switching between 1 way & 2 way flow is done via a simple rotary valve (auxiliary selector valve) located on the side of the machine.

The machine was left in 1 way flow mode in order to operate the hammer (see decal below valve); this would ensure proper operation as well as cycle fluid through the implement so that the customer's complaint could be fully replicated. The only snag with this plan was that the hammer wouldn't cycle in 1 way flow. The lines simply pressurized and that was it. Quite a strange occurrence as the customer was definitely using the breaker before they brought the machine in, there was even fresh concrete dust on, and we hadn't changed anything other than switching from 2 way to 1 way flow. Customer was un-available by phone, so work was continued.

The next step, on a bit of a lark, was to switch the auxiliary selector valve into 2 way flow mode (hammer should not operate in 2 way flow mode in theory, due to design {it is a one way flow set-up, you can't reverse flow and have operation} and the effects of excessive hydraulic back-pressure). Operating the proportional control to the left (which should have cycled the hammer) did nothing. Shifting the proportional control to the right gave full hammer operation, which should not happen. 

At this point removal of the implement lines was attempted to no avail, until the selector valve was moved to the 1 way flow position, which the relieved pressure within the auxiliary circuit. Lines could then be coupled and uncoupled after usage, as long as the valve was switched back to 1 way flow. This confirmed that the selector valve was operating correctly as it was able to dump circuit pressure back to tank; it also confirmed that following the proper procedure for swapping implements prevented any excessive pressure from being trapped. Procedure is to shut off machine, un-hook pressure side first, return side second. This allows all pressure built up in the implement to return to tank, thus allowing easy removal and installation of the hydraulic hoses.

Seems like just another case of educating the customer on following proper procedures, correct? Not quite, remember that the breaker is not operating correctly; the auxiliary selector valve has to be in 2 way flow (instead of the required 1 way flow mode) and the proportional control on the joystick does not actuate the implement when pushed to the left (as it is designed to do) but instead only when moving to the right. Without boring you on all the design details of hydraulic hammers/breakers, I will leave it at the fact that operating a breaker in 2 way flow mode is a very quick way to overheat your hydraulic system and cause some serious damage.

Where do we go to even begin troubleshooting system operation at this point? What we have is an Electro-Hydraulic system (EH), so do we chase electrical or hydraulic first? Do we pull DTCs? Are there even DTCs for hydraulic systems (actually yes, just not on all machines)? Well, much like electrical systems, the first thing I do (whether I am familiar with the system or note) is to pull any applicable schematics & TSBs. In this case there were no applicable TSBs but there were two schematics I was concerned with.

I labeled everything as clearly as possible, though this will not be a hydraulic schematic reading lesson (though I have material on that very subject coming up if anyone is interested). The important things to take away here are overall system interaction. You may also notice that in the hydraulic schematic there is no mention of the auxiliary selector valve; just like any other SI, there is often material left out so keep your head about you. 

Reading over the schematics I was able to determine a few things:

  1. This is a closed center system
  2. While in 1 way flow mode, pressing the joystick trigger or shifting the proportional control full left both activate auxiliary solenoid valve 2 (referred to the electrical schematic as well).
    1. This valve is shifted and sends pilot oil to the auxiliary control valve spool shifting it upwards in the schematic.
    2. This gives us single direction flow. Pressure is applied to pressure coupler (130) and the return side (133) allows oil to return to tank. The flow is generated by oil pump #1, which pops check valve 109 off it's seat thus supplying flow (and as a result pressure) to the pressure coupler.
    3. Return oil is then directed straight to tank, through the valve section, from the return coupler.
      1. In this case, the auxiliary selection valve actually bypasses this section of the circuit and instead allows the fluid to return to tank before it hits the valve
    4. Moving the proportional control to the right, while in 1 way flow mode, actuates solenoid #1 and ends up applying pump flow directly to the line that dumps to tank, thus not allowing any hydraulic action at all, but still maintaining pressure in the pressure side of the auxiliary circuit.
  3. While in 2 way flow mode, pushing the proportional control to the right energizes auxiliary solenoid #1 which shifts the spool valve downwards in the schematic.
    1. This allows reverse flow (pressure becomes return, return becomes pressure)
    2. Pushing to the left actuates solenoid #2 and shifts the spool valve upwards, which maintains pressure as pressure and return as return (standard flow).

Anyone familiar with hydraulic systems know that they are messy, dirty, and oil gets everywhere. You often have to take off multiple other components to get to any one for pressure/flow testing. This carries a huge risk of system contamination, cut or missing o-rings or putting hoses back in the wrong spot. All in all, not something I especially enjoy. My goal is to do as much testing from the seat as possible, so that's why I did.

No scanner needed for this. I hooked up the hydraulic thumb and confirmed proper operation with the auxiliary valve in 2 way flow (as needed for thumb operation), as well as one way operation/thumb drift down when selector valve moved to 1 way flow. This confirmed that the joystick/proportional control/trigger switch and the selector valve were operating as designed.

Next step was to hook the breaker back up and attempt operation once more (in 1 way flow). No operation. Switched to 2 way flow and moved proportional switch left, no operation. What does this tell us? 

  • Well it tells us that when in standard flow (pressure to pressure, return to return) the breaker will not operate (remember it is designed to only work with one direction of flow).

What changes when we switch to 2 way flow?

  • The left proportional switch and/or trigger still energize auxiliary solenoid #2, the only difference being that return oil is now directed through the valve section, instead of directly to tank.
  • The right proportional switch (which allows the breaker to work in this situation) still energizes solenoid #1, what does this solenoid do again?
    • It reverses flow! When the flow is reversed, the breaker works. Well what does that mean?

What is the only logical solution here if everything other than the breaker works correctly, but the breaker only works in "reverse flow"? Occam's razor, simplest solution is normally the correct one. In this case, making the least amount of assumptions meant that the couplers on the hoses from the breaker were on backwards (they are installed from the factory). There is one female (generally return) and one male (generally pressure), this is to prevent mistakes. Though not documented anywhere in our SI, the JD backhoes have a reversed flow from the compact excavators thus necessitating the switching of the couplers to account for this.

I swapped the couplers (got oily in the process unfortunately) and re-attached. Breaker works as designed, in 1 way flow. Problem solved. The hydraulic hoses are also easy to remove and attach as well. Turns out the customer never realized that the breaker didn't operate properly when he bought it, and never followed the correct implement change-over procedure either. So the solution to one problem led to the discovery of another. Customer was fully educated on the correct procedure as well as given a color coded pictorial and video on the proper procedure should they ever need it.

Why this long write up, especially when the entire process took less than 1 hour and the only real work was swapping two couplers and switching hoses back and forth a few times? I wanted to illustrate how far understanding schematics and basic principles can really take you. I also wanted everyone to stop and think about their diagnostic billing practices. Yes, it was a quick diag. Yes, I did very little wrenching; I mostly sat on my butt the whole time. Does that invalidate my results while making me and my time less valuable? Should we give that diagnosis away as a freebie because "I didn't do anything"? I don't believe so. I believe it shows the power of training, practice, and applying the basics; all things that are well worth the investment.

I believe that this diagnosis could have gone a few different way. It could have been a quick shotgun of parts, a long drawn out and oily mess of plumbing in pressure gauges and flow-meters, or just how I did it (80% analysis, 15% testing, 5% labor to remedy the situation). If we as an industry don't validate (and even more importantly support) the knowledge and training needed by techs to complete the job quickly, efficiently, and correctly the first time, then why should we expect them to put in the extra time and effort to do so on their own time?

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Andrew Technician
Claremont, California
Andrew Default
 

Great case study and excellent point that was made..thank you.

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Maynard Technician
Elmira, Ontario
Maynard Default
 

That is really great Chris! I am not a hydraulic guy by any means, but that doesn't matter. Your last paragraph, and more specifically your very last line has some real heavy weight to it. An argument that I think a great number of techs will get right up behind and support hands down!

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Chris Diagnostician
Lansdale, Pennsylvania
Chris Default
   

Maynard, hydraulics is no different than any other field of knowledge. Just a bit of time and dedication and you can learn it as well. We all need to be supported by our shops and bosses when it comes to improving ourselves, as it also improves the shop and benefits the customer; there are no losers. Even more importantly, we need to build and maintain networks, such as DN, with all our fellow…

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Chris Diagnostician
Lansdale, Pennsylvania
Chris Default
 

I appreciate that Andrew. I understand the struggles of what it takes to fix vs what the customer sees. On paper it is a simple swap couplers (or R&R alternator etc.), but we all know the tooling, training, and thinking that go into even seemingly simple jobs.

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Jaxon Technical Support Specialist
Stafford Heights, Australia
Jaxon Default
 

Thank you Chris, I enjoy your presentations: neat, clear and concise.

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Chris Diagnostician
Lansdale, Pennsylvania
Chris Default
 

Jaxon, I'm glad they are of some benefit. I'm hoping we will have at least a few more HD guys posting in the rather near future here. They should be much more entertaining than my own case studies. Keep an eye out.

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Andrew Technician
Commack, New York
Andrew Default
 

Hey Chris you should check this guy out if you haven't already, his name is Brendan Casey and he's a technical trainer and expert on hydraulic systems. hydraulicsupermarket​.​com/technical​.​html He has a blog of sorts where he sends out an email regarding some case in point now and then. Not a case study like you have here but very interesting and worthwhile…

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Chris Diagnostician
Lansdale, Pennsylvania
Chris Default
 

Andrew, I appreciate the links and I'm glad to see automotive techs putting some research into hydraulic systems. I stumbled across Brendan a few years back and refer back to his site from time to time. He's a great resource for anyone to keep around, especially if you don't deal with hydraulic systems on a daily basis. I happen to be a bit spoiled in the information sector as I have a rather…

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Andrew Technician
Commack, New York
Andrew Default
 

When I was first learning the trade I put a really hard effort into understanding electrical and hydraulic systems. Besides Brendan Casey's book I also picked up a second hand copy of the first edition of this book, which seems great, though I haven't had time to read it much: amazon​.​com/Mobile-Hydraul… Working in automotive we don't have that much exposure to hydraulic…

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Chris Diagnostician
Lansdale, Pennsylvania
Chris Default
 

Andrew, Excellent stuff. If you aren't growing then you are dying. It is always great to see people wanting to learn more and more about anything they can and I commend you for it. Brief aside, combination flow pressure meters are quite expensive, usually around $5-$10k depending on level of quality (though there are always cheaper ones available), so a lot of hydraulic techs have never seen…

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Andrew Technician
Commack, New York
Andrew Default
 

Thanks!

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Keith Diagnostician
Staten Island, New York
Keith Default
 

Great write up Chris !

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