Hydraulic cylinder repair

[GuillermoMarrufo]

We are repairing a heavy duty cylinder of a 200 Ton vertical plastic injection machine that was severely scored and damaged (both piston and sleeve). My question is regarding the clearance between both. We found 0.020" (0.010" per side) on original undamaged areas. Is this normal? Seems too much to me. Sleeve diameter is 12.604", piston is 12.584". After TIG welding and honing, the sleeve lost dimension. We now have 0.024 to 0.027". Also, the two seals or packings of the U type were totally damaged. We had to cut them to take`em out. Their grooves are 0.690" wide x 0.625" deep cut on a solid piece, there is no way to dissasemble the piston (no piston cap) to install them. Is there a safe method to stretch them to fit into the grooves? They seem to be made of a synthetic plastic. Thanks for your input

 

[FOETS]

The diametrical clearance looks too big to me also, as you suspect.
The clearances and tolerances are all dependant on the seal. You would need to look up what is the maximum allowed from the seal manufacturers specifications to be absolutely sure.
I have a diametrical clearance allowable to a max of 0.012" by a generic chart for that bore size.
Cylinder specifications on mobile equipment hydraulics specified as H8 - e9 easy running fit
Seal groove should be JS11.
Again this needs to be checked with the specific seal manufacturer

You should try put this query also into the Fluid Power forum.

FOETS
"social drinker with a golfing problem"

 

[EdDanzer]

The clearance is a function of pressure, seal type and guide bearing type. 0.020” is large for urethane U-seals if operating over 1000 psi. Typically scoring is from side load or contamination. It appears this has been repaired before. 12.500” would be a starting diameter. The continued honing when repairing is increasing the bore to a freak size. This will cause seal problems if a standard seal is used.
You will need to post the operating pressure for more information.