Clean Hydraulic OIl

[John C.]

Summary Case study; Excavator was overloading the engine once in awhile. No fault codes. Some troubleshooting done and adjustments made to lessen the problem. A week later the problem got worse. Troubleshooting included checking pressures on both main and load sense circuits, pulling suspect screens in the control passages in the valve and pump controls. Proper load sense pressure was getting back to the pump. Rear pump seemed to be "hanging on stroke" so the end caps were pulled and the servo piston had to be hit with something to move it. The pump was removed from the machine and the rear section disassemble to check. The following photos show what was found.

 

[John C.]

The large looking scratch is just a mark and isn't relevant to the problems. The circular scratches are relevant and many can be felt when you pull your finger nail over them. Also not the little notches on the barrel assemble ports. All you see here indicates foreign material in the oil. The photo below shows the little notches and subsequent erosion. The next photo shows the saddles that the swash plate sits in. The last in this reply shows some scuffing on the high pressure side of the saddle.

 

[John C.]

The little bit of blackened area seems to be a clue. Photo below is the low pressure side of the saddle and note some more blackened area and the mottled appearance in the brass. The mechanic stated there was plenty of brass
slurry on the cradle when the swash plate was removed. Note the brass on the mating surface of the swash plate.

 

[John C.]

The high pressure side shows some scuffing as well. I'll post a few more things after a bit.

 

[Nige]

That disaster's got big $$ signs written all over it.............

 

[John C.]

The servo valve spool also has some problems. The issue with this is the oil that gets into this spool and cavity is from the load sensing circuits and not what is in the pump cavity. There is a spool inside this one that also is part of the control circuit and at this point the client is going any further.

 

[John C.]

The survey of damage to this section of the pump then shows there was debris inside the flow control servo valve spool which could have been most of the cause of the pump not de-stroking. The other damage was to the cradle and swash plate. When I put the swash plate in the cradle and tilted it like it was stroking up it moved well until it hit just shy of full stroke and at that point it would stick and not move at all. I had to physically pick the plate up slightly in order to be able to rotate it back to level. All this fits the scenario of when the pump was working at less that full output systems worked, but when pressure and flow were maxed out the swash plate would be stuck and not destroke until after after the control was moved to neutral for a couple of seconds.

The machine has a bit over 7,000 hours on the clock. I have no history as to use or maintenance practices. A shear was installed on the machine at time of failure. We have described the damage to the pump but what is the root cause of the failure? The client is going to install a reman pump back in the machine as soon as possible. What other issues might one expect to see in the future? What other work should be considered before putting the machine back to work?

 

[John C.]

After letting this situation stew in my mind for awhile I started thinking about the progression of the failure. First thing in my thinking was the the realization the load sense oil coming back to the pump from the main control valve has no filtering mechanism. Any garbage that circulates inside of that valve can possibly flow back to that servo valve in the pump. There are a couple of small screens in passage ways inside the pump. However they would only catch something actually visible to the naked eye. All the damage on the servo valve along with the scratches in the bore seems to indicate that is what happened. I had asked the mechanic if he had pulled the filters and strainer in the tank and he reported that he had and saw nothing. He did say he noticed that when he operated the shear, the stick would creep without moving that control. With that piece of information I'm trying to find other places or reasons oil from the shear circuit could get to the stick circuit. Right now all I can think of is the compensators which are on the load sense circuit and can connect to the pump servo valve as well.
The next issue is the damage to the saddle that held the swash plate. What I saw didn't strike me as being a lot different on other pumps I've seen and rebuilt in the past. The saddle itself is some kind of bronze or brass and the swash plate is some kind of high tech steel. The odd thing was the fact that the swash plate would stick in place at a high output position. It seemed that the plate was not sitting exactly square in the saddle. The only thing that holds the plate in place is the pressure on the front of it by the piston and barrel assembly internal spring and the seal and discharge plate. The wear on the seal surfaces of the piston and barrel assembly and the seal plate I have seen before. The little notches at the back sides of the barrel ports I believe is erosion because the seal surfaces were no long perfect. Did any of that have anything to do with the stroking issue? My thoughts are that it didn't. I've seen plenty worse in the past so for the most part just put that wear to normal wear and tear for its age. An exchange pump will take care of all that.
So the list of work is getting longer.
Replace the pump with an exchange.
Remove and check the compensators on both the shear and stick circuits.
Remove and disassemble the stick and shear cylinders, inspect for damage. Repair as necessary and re-install.
Replace hydraulic filters and oil.
Test run machine checking cycle times and pressures on all functions. Repair any discrepancies.
Return to service.
I'll let you know when the machine is back up running again and try to provide some conclusions on the reason for failure and some of costs involved.

 

[Nige]

John, I appreciate that this is a situation where not all the oil in a system gets filtered before reaching critical items like pump load sense controls that have tight tolerances, but would there be anything to be gained in going to finer filtration elements on the rest of the hydraulic system in an attempt to remove a larger percentage of particles at the smaller end of the size range..? I have no idea even if that's possible or if any options are available either from the equipment manufacturer or aftermarket. You never mentioned it, but I assume that the equipment owner wasn't having oil analysis performed on the hydraulic system..?

In addition to your proposed list of work above, would there be any benefit gained in kidney-looping the machine (probably more than once) after the oil and filters have been replaced..? It'll probably take a while for the small particles stuck in corners everywhere in the system to start migrating.

 

[John C.]

Nige, that's a good question and at this point I'm not sure of an answer. The installed filtration in these machines is very good to start with. The only flow paths that aren't filtered that can bring those fine particles back to the tank would be the motor case drain circuits. Client has been warned of future issues with those components so at the moment we aren't saying that it is necessary or ruled out. We will know more after the stick and shear cylinders are checked and the reason for the stick circuit creep is figured out.
As I recall there is a mathematical procedure to kidney looping that requires a certain amount of time with the filters in the loop to ensure all the oil gets the additional filtering. I've been part of one project in the past on a big machine that required more than three hours of operating the loop to obtain the theoretical coverage.

 

[Nige]

There are kidney loop machines out there that have built in particle counters. We have a couple here on site. Basically you keep filtering the oil until the particle count goes below a certain value. Sometimes it’s necessary to run the machine and exercise circuits where oil may be dead-headed. It’s funny to watch the ISO Code jump by a couple when you do that.
Otherwise a portable particle counter is another option.

 

[John C.]

There are companies here that sell permanent mounted loop systems that are like the old Cummins bypass filter setup. I've never heard of a machine that can count particles while in operation. Can you post any information that you have on them?
I don't know if that would be something that could be sold to end users around here. Prevailing thoughts are that staying within manufacturers specifications, you won't have problems.

 

[Nige]

I’ll post some links tomorrow when I can work from a computer rather than a phone.

 

[mg2361]

http://www.deere.com/media/player/p...percaddy_m.flv&autostart=true&r=-1&height=270

 

[Nige]

There are companies here that sell permanent mounted loop systems that are like the old Cummins bypass filter setup. I've never heard of a machine that can count particles while in operation. Can you post any information you have on them?

The only brand I would personally endorse is CC Jensen. Used them many times and never been disappointed. I'd be looking at an HDU15/25 for an excavator hydraulic system, it would only require an 24V supply to run the pump. http://cc-jensen.com/index.php?m=p&pid=27

I think maybe we were talking at cross-purposes regarding the particle counter. I was referring to an external filter cart with a built-in particle counter so that you can see the oil clean up as it is kidney-looped. Again CCJ supply that type of machine, as I said before we have two of them. See photo below, the particle counter display is circled in red. As we see it the advantages of this filter cart over OEM-supplied carts are:-
a) It's electric, so no air pump banging away all the time.
b) It has 60DegC heaters for heavier oils, speeding up the process.
c) The particle counter produces real-time cleanliness results.
d) It's cheaper than OEM units that don't have any of the three advantages above.

 

[Nige]

I don't know if that would be something that could be sold to end users around here. Prevailing thoughts are that staying within manufacturers specifications, you won't have problems.

I explain it using the comparison of - it's like buying clothes - "one size fits all" may fit, but it sure as hell isn't going to fit you like something that was tailored.

 

[John C.]

Thanks for the web site Nige. A bigger perceived problem than the particle count in this neck of the woods is entrained water in the oil. The web site gave me some good ideas of a way to sell the service. Large companies in this area already have the loop filtering or contamination requirements with new oil suppliers. It's the small companies where "good enough" makes a lot of standard engineering practices a hard sell. Would you know any ball park costs to a system like you have in the photo?

 

[Nige]

TBH I would say that particles played a much larger part in the failure you describe above than water, but that may be an exception rather than the norm.
Either way CCJ filters can pull both particles and water out of an oil, it's simply a matter of selecting the correct filter element.

Don't get too freaked out, but the filter cart in the photo above cost a hair over $30,000, but it is very much in the way of a "special" in that it will handle everything up to EP/FDAO gear oils, so it has all the bells and whistles. For something like hydraulic systems a much simpler filter cart is available. I would be looking at the PTU2 27/27 unit and in the write-up it specifically states that it works for "offline filtration of water-contaminated hydraulic oil".
http://cc-jensen.com/index.php?m=p&pid=147
Unfortunately I don't have a recent price for it, and I don't know if it can be had with a particle counter built into it. The best thing I could suggest is that you make contact with CCJ in Atlanta. If you want details of a contact, etc, PM me and I'll gladly give you the name of the person at CCJ I've dealt with for years.

 

[Welder Dave]

Here's a Donaldson filter cart and a Parker filter cart. There are others but Donaldson has filter elements down to 2 micron and filters for water. The one I rented was home made but used Donaldson filters. They start around $2000 I believe for a basic filter cart but could be home made too. The better ones have indicators to tell when the filter needs changing.

https://www.donaldson.com/en-us/engine/filters/products/hydraulics/off-line-filtration/filter-cart/

https://www.parker.com/Literature/EMHFF/HFD_Catalog/HFD_Catalog_Filter_Carts.pdf

 

[John C.]

I've used filter carts before. Usually it was for big corporations that wanted new oil filtered before it was put in a new machine. After the machine was delivered the carts didn't get used again.
The reason I bring up water is because it can be seen in hydraulic oil by color. I have a few machines in my area that sit for long periods of time and always pick up water in the oil. Color turns white and the only remedy is to drain it and start taking hoses and fittings loose to get rid of what is in the circuits. Even that is not the best way to clean the system. I might be able to sell a service on those merits. As for the particle count and running a loop system on this machine go, it's a non starter for this customer at this point. I'll know more when the other work is finished.