Hydraulics won't hold

[arcamm]

I just picked up a Terramite Model 1 backhoe. The out riggers will not stay up or hold the tractor when lowered. There are no external leaks, so I'm assuming everthing is internal. Where should I start looking? Would it be the pistons in the cylinders or the spoolers?

Thanks, Ron C

 

[wdchyd]

Troubleshoot with a pressure guage or start with the pistons.......the piston seal inside is probably worn and bypassing.....you won't see any oil leaking if it's the internal piston seal......

 

[J_J]

If the relief for the BH does not activate with the cyl are fully extended or retracted, then you have a leak in the cyl as wdchyd mentioned. Remote possibility could be a worn outrigger spool, but unlikely. Are both outrigger cyl doing the same thing?

 

[arcamm]

Yes, it's both cylinders are doing the same thing. I suspect some of the others are as well, I just got it running yesterday. The machine was setting for quite a while.

 

[J_J]

How many times have you cycled the outrigger cyl. Do they totally collapse or feel spongy?

Cycle them about ten times and see if there is any difference.

I would suggest a hyd gage and test all the cyl.

 

[arcamm]

They have been moved up and down atleast that much, but I will run them through 10 full cycles to make sure. They will lift the tractor, but they bleed down in less than a minute.

 

[Bison]

I would look in the valve block for a broke load valve spring or something.
Even if the cyl piston seals leak,the legs should hold in the push downstroke.And slip back just a little till the pressure is equal on both sides of the piston when you let go of the lever,they'll just extend slower due to bypass to the return side.

 

[J_J]

You never did say if the relief valve activated at full extend or retract. Any idea what the BH relief valve setting is?

You could add a needle valve to the extend cyl hose. and raise the outriggers, then tighten the needle closed, and see what happens.

That should lock the fluid in the base end. If the cyl leaks sown, it is for sure, bypassing.

 

[arcamm]

I'm guessing it does. I'm basing that on the engine not dead heading when the piston reaches the end of the stroke. No idea what the settings are.

They will hold position as long as I have the lever pushed, but as soon as I release it, they start to bleed off. Both side act the same and bleed down a pretty much the same rate.

 

[AKKAMAAN]

This Model 1 Terramite is from between 1965 to 1972....cant find a good picture of it online....

Main relief is not in the picture when outrigger cylinder is bleeding down. Control valve in neutral makes work ports closed.

If piston seal is leaking and capped side holds the load, cylinder rod is retracting and that rod volume of oil must be displaced through the control valve, if there is no external rod seal leakage. Only an eventual work port relief, or spool could leak. If piston seal is leaking, pressure will equalize on both sides of piston.

Bleed down in one minute do not tell the entire story...diameter size of rod and how long retract will determine leakage volume....

OP should also make sure this old control valve really sets in the real neutral position, maybe it is sticking a bit and not closing the work port properly...spool stiction from rust etc could cause bleed down too....if spool is 1/32-2/32" off from neutral could be enough....

 

[J_J]

The odd thing, is that both outriggers are doing the same thing. On the BH relief, it should be set equal to the main PRV. If he is pumping fluid into the cyl's, and the relief never activates, the fluid is going somewhere. You are right, there is no relief in a static situation. The leak is in the cyl's or the spool, or both.

 

[arcamm]

If it helps, the cylinder is 16" eye to eye, 1" rod and 2.5" cylinder. Two cylinders, two valves doing the same thing. I'll check to see if they off center.

 

[J_J]

If you put a gage in the rod end of the hose, you can watch the pressure equalize if the piston seals are bad.

 

[wdchyd]

arcamm,

If it turns out to be the control valves, be prepared to do a complete clean and rinse out of the reservoir tank (including rag clean in bottom).......if multiple valves are worn it almost always points to contaminated hyd oil grinding away at spool tolerances.....as least you have a gresen valve bank and replacement sections can be had to repair this situation......

Best to test and troubleshoot like you are doing to eliminate doubt....:thumbsup:

 

[glastron23]

AKKAMAAN... wondered when you were going to jump on this one.... totally agree that the valve bank is your problem and not the packings. this is a going to be REALLY GOOD discussion.... Jim

 

[AKKAMAAN]

AKKAMAAN... wondered when you were going to jump on this one.... totally agree that the valve bank is your problem and not the packings. this is a going to be REALLY GOOD discussion.... Jim

Thanks Jim!
Cylinder drift is to many times misunderstood. Piston seal many times in fault but, but in retract mode like this there is always an additional problems due to the cylinder rod displaced volume.

Now we now a little more about what volume that are leaking per minut...

Great to see these pictures.....seems like cylinders are bleeding down 4-8" on the rod....that will make 3-6 cubic inch per minute...

If piston seal is bad, pressure intensification will boost pressure to 6.25 times higher than work pressure that lift. If it takes 500psi to lift up excavator, drift pressure will be 3125psi....and an eventual work port relief will open...

This will happen even with a good piston seal, but at a much slower cylinder drift, which would be considered normal...

 

[arcamm]

I need a flash course in hydraulics to get me in the game.

One other thing I observered, on the left side outrigger, there were a couple of times when I was trying to get the machine up on the riggers that when I pushed the lever to lower the outrigger, it would come up instead of going down. I would return to neutral (and actualy go in the oposite direction because I thought I was moving the lever the wrong way), then go back and the ram would go in the right direction.

 

[AKKAMAAN]

I need a flash course in hydraulics to get me in the game.

One other thing I observered, on the left side outrigger, there were a couple of times when I was trying to get the machine up on the riggers that when I pushed the lever to lower the outrigger, it would come up instead of going down. I would return to neutral (and actualy go in the oposite direction because I thought I was moving the lever the wrong way), then go back and the ram would go in the right direction.

My picture is pointing out (fingers) the position for the work port relief valves that could cause the bleed down...try to find the ones that are connected to the outriggers, I cant tell if there is and valve cartridges in them slots or not....
Please post a detailed picture of both sides of the valve stack??
The valve should be on the same side as the lever, if you push the lever (spool) to lower outriggers/extend cylinders....

About the other observation you had...

....when I pushed the lever to lower the outrigger, it would come up instead....

If you can't repeat it, "it never happened"...LOL....IMO it can be ignored for now...

 

[arcamm]

Here's some more pictures. Does this help?

 

[wdchyd]

It looks like the valve castings are machined for WPR's but are plugged.......

No WPR's......