Improving hydraulic bottle jack

[tonyfoale]

A while back I detailed how I upended a bottle jack for use in a press.
See here http://www.homemadetools.net/forum/i...5188#post81319

It has had quite a bit of use and has worked fine. However, it recently developed a leak and dumped most of its oil over the floor. External inspection indicated that the oil had leaked through the ram wiper seal. Normally when the jack is right way up this seal is at the top and should never get flooded with oil and is only there to wipe oil off the ram and keep dirt out. When the jack is turned upsidedown there is oil wanting to escape 24/7, although that seal should be up to that duty it decided not to after some time.

I pulled the jack apart, I want to make some more mods to it and this was the motivating opportunity. I hadn't done it previously but I withdrew the ram and piston assembly and was fairly horrified to see that the cylinder appeared to be just a piece of thick walled DOM tubing with no refinishing, honing or grinding. Not ideal for a high pressure seal. This has a 55 mm piston and is "supposed" to be loaded to 16 ton. A quick calculation shows that the loaded pressure will be close to 60 MPa, that's not a trival pressure.

I decided to hone the cylinder to give an improved surface for the main seal. I have a high end cylinder hone but its minimum diameter is 72 mm so I had no choice but to use a Horror Fright version which would close down small enough.

Click on photos for full size.

Honing setup. Normally I use recirculating flood honing fluid to remove the refuse but that wasn't practical in this case because it was a blind hole, so I 3/4 filled the cylinder with fluid to at least get the junk away fro the honing surface. It would have been much easier if I had unscrewed the cylinder from the base but it resisted all my efforts to do that. I was concerned that any increased effort would distort the cylinder.



Here is the cylinder after a short bit of honing. The photo doesn't show all the way down inside but that pattern was repeated all the way down. It is obvious that there was a spiral high point around and along the cylinder. This was an even greater shock than finding the surface unfinished. I debated whether to leave well enough alone or continue honing until the spiral was gone. As best that I could I used a bore gauge to determine how much would have to come off to clean it up properly. It looked like I'd have to take about 0.05 mm off the diameter of the high spots to get the surface down to the low spots. I considered that preferable to the spiral so I continued honing. Rapid metal removal is not a strength of the HF hone and I had to hone away for half an hour to get the job done. My estimate of the final diameter was pretty close and I wasn't concerned that the seal would find it too large, on the other hand the seal should be much happier with a round cylinder.



The cylinder after honing. Compare to the initial spiral above. A quick test assembly demonstrated a more solid feel to the operation of the jack, previously it had a slight sponginess, that has now gone. In use the main piston seal must have been leaking a bit into the outer chamber, giving the non-solid feel. Tomorrow I'll finish the planned modifications and assemble it back into the press.

It is never good practice to place any body parts under anything only supported by an hydraulic jack, and the findings here only serve to emphasize why.