Cat e120b hydraulic bleed off HELP!!!

[Mcbride124]

I have a old cat e120b machine... its an old hoe but dependable. Recently after pushing its limits handling large stumps the mainstick cylinders will bleed off fairly fast. If it doeant have a load in the bucket i can bump the controls to get it to stay in place... leading me to believe a control valve blown o ring possibly? Cylinders are dry just scratching my head on it and like having the machine around. Any help appreciated

 

[Bls repair]

Sounds like an internal cylinder leak.

 

[Mcbride124]

But to have both cylinders be leaking internally? Because one functioning properly would hold it up... when controls are in nuetral it acts like the control is being pushed

 

[kshansen]

Sounds like an internal cylinder leak.

One way I have used to test for internal leaking in a cylinder involves blocking off one port of the cylinder and then apply pressure to the opposite end and check for movement.


An example for the cylinder above. If you disconnect the line from point "A" and cap the line and the port on the cylinder then operate machine to put pressure into port "B" if there is leakage past the piston seals after first moving in the ram will start moving out. This works best when ram is disconnected from what ever it normally moves! Also if cylinders are working in pairs it is a good idea to test both at the same time by blocking the "A" ports on both. This will let you know which one is the problem.

All appropriate safety precaution should be taken to support things that could drop and keep people away from pinch points.

Anyone have better ideas or different methods feel free to comment, like they say "There's more than one way to skin a Cat!"

 

[Hydraulic Cylinders Inc]

It does sound like internal Bypass. Might have blown the piston seal.
Another test you can do for bypass is retract the cylinder all the way, Disconnect the hose on the extend side and install a ball valve or leave open and slowly pressurize the retract side. There should be no oil coming out of the extend port, If there is then there is a internal bypass problem. Doing a midstroke test is the best way as describe above. I usually put a dial indicator on the rod to check for movement. Doing a Midstroke test can be dangerous. You really want to make sure you can get as much air out of the cylinder as possible. Easiest way and safest is the first way i mentioned

 

[Hydraulic Cylinders Inc]

If the oil ring on the controls was blown you would see it leaking on the ends of the control valve. There usually is no oil rings on the spools. The oil rings usually only seal on the end covers of the of the valve

 

[dirthog]

But to have both cylinders be leaking internally? Because one functioning properly would hold it up... when controls are in nuetral it acts like the control is being pushed

One will NOT hold it up as they are plumbed together so if one is bypassing it will just bleed the other side off also.

 

[John C.]

I take it this machine doesn't have the load locks on the boom cylinders? If the cylinders check out OK and you don't have load locks then from your description of the drift stopping when you touch the control, I would suspect the lift check in the control valve.

 

[Mcbride124]

Yes when in is bleeding down and i pull the control safety lever on the side it stops bleeding.... if it were internal on a cylinder one would think it would continue. Cylinders checked out ok

 

[John C.]

That seems to indicate to me that you have a pilot system issue that is partially activating the spool for the boom down function.

 

[Hydraulic Cylinders Inc]

I would agree with the pilot issue. Seems like it's not closing when you have them in the neutral position.