Blowing out o-ring, stumped, need help!

[rScotty]

An interesting problem. I guess the first thing I would do is to make sure I had the right O ring material. Then Pressure and then Temperature. All of those are capable of being checked by most mechanics. An inline pressure gauge can be made up for under $50 and is handy to move around to different places for all sorts of diagnosis. I leave mine in the loader line.

On materials, O rings are often misunderstood & wrong material used. I had a lot of problems at one water treatment plant until we finally figured out that the tech was using vaseline instead of silicon grease to hold the O rings into place on the city's big power water pumps he repaired. Vaseline seems perfect, but there is some chemical reaction that caused the O ring to expand, lose hardness, and crawl right out of the O ring groove. Changed that and no more problem. We would never have figured it out if someone hadn't run short of O rings and tried to put some that were stored with the vaseline on them back into the O ring groove. We found the spares had all mysteriously become way too large to fit, and BINGO! we had found the problem!
Go to Mcmaster.com & look up O rings for a quick overview on materials.

rScotty

 

[ArlyA]

But didn't the original ring blow out? Installed at the factory.

 

[LouNY]

You can get o-rings in many configurations.
I have had good luck with tough sealing applications with an X style sealing ring or a Quattro Cross Section o-ring,
and even a square profiled "o-ring".
It may fix the issue especially as all pieces seem to be in "spec", the tolerances may be additive in nature allowing too much clearance or not enough crush on the proper o-ring.

 

[oldnslo]

Rscotty
What type of seal material was being used on those water pumps? I 100% agree some materials are not compatible with oil but I also suspect vast majority of O-rings used in hydraulics are nitrile- Buna N or viton - fluorocarbon.

I still suspect surfaces not flat as main culprit since there needs to be a gap for the O-ring to extrude.

 

[rScotty]

Rscotty
What type of seal material was being used on those water pumps? I 100% agree some materials are not compatible with oil but I also suspect vast majority of O-rings used in hydraulics are nitrile- Buna N or viton - fluorocarbon.

I still suspect surfaces not flat as main culprit since there needs to be a gap for the O-ring to extrude.

Oldnslo,
I don't know the original O ring material. In the water pumps I mentioned they were part of the supplied repair kit. Keep in mind that the application I mentioned was cold water, not hydraulic oil. I only brought it up so as to point out that there are some weird material compatibilities involving O rings.

To the engineer's surprise, the incompatibility between Vaseline and some O ring materials turns out to be a well-known problem. Check it yourself. Smear some O rings and put them in a baggie. It's not a little change, it's obvious. Or google.

Getting back to the OP's stump grinder. My preference would be not to use Buna-N - even the oil resistant types. Not enough high end temperature range. I'd rather go Viton there - but I have NOT checked for hydraulic oil compatibility.

I agree with your thoughts, and also suspect the surface flatness. Did you notice in the exploded diagram photo how thick that metal is where the O ring failed? That is one seriously thick chunk of steel. I wonder why so thick?

rScotty

 

[oldnslo]

That end plate appears to only be held on with two bolts so thickness would be to resist bending from pressure.

 

[Venturabass]

Hey Folks, thanks for the comments.

I was not present when the dealership took the valve apart to inspect. They told me the "mic'd" the surface and found it was flat within spec. I asked them did you measure gland depth, they replied yes, and that was all that was said. I should probably question them again if the problem returns.

Interesting point on chemical compatibility if they used something to "hold the orings in place during reassembly". I don't know the answer to what they did.

The first time it failed was the factory installed orings, and they found a bolt that could be turned by hand. We all passed it off as that, seemed obvious. The second time the bolts were not loose. In talking with a different dealer they have told me they've seen this oring fail on these Kiotis, but only when it was literally brand new, and problem never returned. They've always passed it off as not being seated right from the factory, but you'd think that would be more accurate than during a repair.

My gut says there's something about running that hydraulic loop. Dealer did hook the tractor up to a giant brush hog, (no hydraulic connection), and let it run for 2.5 hours at operating speed, lifting the 3ph multiple times to see if it would fail. There was no failure. I've since been running my PTO wood chipper for the last 3 hours and doing loader work, no failure.

I've talked with folks at dealers/Woods/Summit Hydraulics/Michigan Iron about temperature being the factor. The hydraulic folks seemed to think not.

I'm thinking of buying a test gauge from Ken's Bolt On Hooks, maybe a temp gauge too if they sell them, and doing my own tests. Curious what I get for readings both up and downstream of the grinder's valve, and after working for awhile. These pumps don't make pressure unless loaded up with resistance (hoses, valves, orifices) or are lifting a load. If I perform my order of operations while grinding might I see a backpressure spike that doesn't make sense?