How did this happen!!!!!

[Chris in IN]

I went out after supper today to dig out some 4" & smaller tree stumps with my JD4400 & 48 hoe. It was just getting dark and I was about to quit but decided to do one more. I was reaching over and digging behind the stump trying to pull it out. I went to tilt the bucket back, it made a loud squall and stopped. I got off to see what the problem was. I could not believe what I saw. The bucket cylinder shaft is now bent in an L shape. Has this happened to anyone else? I knew I should have gone back to the shop and worked after supper.

 

[JerryG]

Yes, Chris,
I have had it happen. I had a hose clamp on the suction side of the hydraulic pump under the tractor behind the loader frame that didn’t fit right. Air was being sucked in and the fluid was aerated. Sense the fluid was aerated, the relief valve wouldn’t work. Know telling what kind of pressure it was running. Had a real chore trying to find the problem. My dealer checked and tried every thing. I wound up finding it myself. The simple things are some times the hardest to find.
JerryG

 

[dmccarty]

Chris,

OUCH! What has the dealer said about this? How much is it going to cost to fix?

Thanks.....
Dan McCarty

 

[JOR_EL]

Jerry,

Can you explain how the fluid being aerated prevents the relief valve from working? I would have thought pressue-is-pressure in a closed system, and X psi would cause Y effect, aerated or not. (but I'm sure not knowledgeable about these hydraulic valves, etc /w3tcompact/icons/blush.gif )

Thanks,

Larry

 

[JerryG]

Larry,
Fluid is not compressible. Air is compressible. If the fluid is hyper-aerated then the fluid then acts like it can be compressed. The air acts like a shock absorber to the relief valve. It’s like a sponge pushing against it instead of something solid.

 

[JOR_EL]

Jerry,

I understand the compressible/non-compressible issue, ..and can see there would be a "shock-absorber" effect. But after the shock is absorbed, and the air is compressed, you have a certain psi acting on a certain surface area = a certain force in lbs. = an open relief valve.

The fact that air is compressible doesn't stop relief valves on air tanks from opening. Since the hyd. fluid pump is working with an adequate volume of fluid to make up for any loss(in volume) due to air-compression in the system, I don't see how the relief valve action would be affected.

I also find it interesting that the pressure would be great enough to bend the cylinder-rod, ...(air-compression or not) but NOT great enough to activate the relief valve. /w3tcompact/icons/shocked.gif !!??

Interested in more opinion! /w3tcompact/icons/smile.gif

Larry

 

[heehaw]

when things like this happen, an i can't figure out why, i chaulk it up to the ole saying, stuff happens..if it could break, it will; etc etc. sorry you had the problem, but it may never happen again, we hope/
heehaw

 

[MJB]

Just throwing out another theory on aerated oil and relief valves. I see this often in air conditioning system design. In the case of a liquid passing through an orifice (or relief valve) there will be a certain flow rate which is proportional to the size of the orifice and the pressure differential. If a gas is mixed in with the liquid the flow will "choke" as it passes through the orifice causing a much greater pressure differential than it would if it were all liquid. It may be possible that the relief valve is opening but it is to small to allow enough flow of highly aerated oil to pass through to relieve the pressure from the pump. Just a theory.

Fugitive from the Cubicle Police

 

[JOR_EL]

[[[It may be possible that the relief valve is opening but it is to small to allow enough flow of highly aerated oil to pass through to relieve the pressure from the pump.]]]

Thanks for your comments, MJB, /w3tcompact/icons/smile.gif.

I realize there's a lot to know about this stuff, ...just trying to make sense of what little I do know /w3tcompact/icons/tongue.gif !

Larry

 

[Chris in IN]

I have been busy and have not checked back for a while. I got my backhoe repaired. The dealer covered it under warranty. The first day I got it back I dug stumps for 2 straight hours, including the one I was working on when the cylinder bent. I did not have any problems. I worked it hard to see if it would do it again. The next day I dug stumps for another 4 hours without any problems. The service man could not find any reason for the cylinder bending. He adjusted the pressure and checked the clamps on the suction line.