hydraulic question

[Sammy3700]

My woods BH7500 has started to leak down (boom cylinder more than others) I am thinking the cylinder is leaking by internally. It digs great just as soon as you turn loose of the handle with in 5 seconds it is on the ground. Thanks for any thoughts.

 

[/pine]

It "may" be just a lose nut on the (bottom of) valve spool...?...You might check to make sure the nut on the bottom of the spool (or detent if there is one) is tight...a loose nut will not allow the spring to seal the spool ports on return to center...

 

[Dave M7040]

My woods BH7500 has started to leak down (boom cylinder more than others) I am thinking the cylinder is leaking by internally. It digs great just as soon as you turn loose of the handle with in 5 seconds it is on the ground. Thanks for any thoughts.

Often there is a small O ring between the piston and the push rod which splits and allows this to happen. It is unlikely the seals on the outside of the piston.
You need to carefully remove the piston from the push rod and look for an o ring which seals the gap between the parts. I guess you could look on Messick's web site to see if the cylinder is built as I describe. don't buy a rebuild kit as you may only need to go to a hydraulic shop any buy the o ring or two for a couple of $ rather than an expensive kit for each cylinder.

Dave M7040

 

[J_J]

The problem could be caused by cyl seals or worn valve spool.

The valve spools are a metal to metal precision fit, and they don't make replacement spools.

The only spool o-ring might be where the spool exits the valve body. Some have them, some not.

 

[Sammy3700]

Thanks for the info gentlemen. Ran it some more today and am thinking it is in the valve body someplace instead of internal cylinder. I swapped the boom cylinder with the dipper stick since they were the same size. All the cylinders are leaking to include the stabilizers some faster than others as to how much weight is on them.

 

[J_J]

If you want to know for sure, install a needle or shut off valve in the base line to the cyl and then raise the loader and then shut off the valve. Shut off engine.

If the cyl doesn't fall, then you know the leakage is in the valve spool.

Here are some valves to look at for replacement. Match up valve flow with pump flow.

Surplus Center

 

[J_J]

Checking leakage in a cyl using two identical hyd gauges.

Place a hyd gauge in the base end and a hyd gauge in the rod end.

Cycle the cyl about 5 times to exclude any air.

Grab a load to cause a pressure of about 1000 psi, and shut off engine.

If you see pressure in the rod side, guess what, something is leaking, maybe one or both seals are leaking.

How much can the rod move you say. How about until the pressure equalizes.

To those that believe that fluid does not transfer across bad seals, take your best guess and explain how the pressure can build on the rod side.

A perfectly good seal will not leak and therefore should have 0 pressure on the other side of the piston.

I have told you how it can happen, so tell me again how it can't happen.

Just how does that fluid get to the other side and cause the pressure to build.

Some of you will probably still disagree, but I really don't care anymore.

That's my story and I'm sticking to it.

 

[Sammy3700]

I thank you for the info J.J. I agree it will pass by the seals internally I just was not sure how to determine if it is doing so I will check the way you explained it. Thanks again.