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.

[j.bickley]

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.

Good point! Thanks.
---Joe

[DIYer]

Thanks tonyfoale! We've added your Cylinder Honing Setup to our Drilling and Drill Presses category,
as well as to your builder page: tonyfoale's Homemade Tools. Your receipt:

Cylinder Honing Setup by tonyfoale

tags: honing, cylinder

[nhengineer]

Tony, excellent report. Next time you need to remove the ram cylinder, put the jack base in a large vice (at least 6"), well anchored to the floor, use a big MF pipe wrench with a long pipe (36") slid over the handle for more leverage (better use a Rigid, a Horrible Freight with probably bend or break). Finally, put the ram back into the cylinder exactly where you going to apply the pipe wrench (preferably at the very bottom). Get as close to the bottom as you can since the combination of the cylinder screwed into the base and the the ram on the inside will prevent distortion. I've been rebuilding jacks for 40 years and I have yet to deform a cylinder. When you put everything back together, use the same method. The internal pressure of a service jack is around 30,000 PSI so that requires a great deal of torque to seal up. Keep up the good work.

[tonyfoale]

Tony, excellent report. Next time you need to remove the ram cylinder, put the jack base in a large vice (at least 6"), well anchored to the floor, use a big MF pipe wrench with a long pipe (36") slid over the handle for more leverage

This is basically what I tried, but I got to the stage where I got concerned about breaking something. I had to google what a MF wrench was, it was what I tried but I am used to them being called Stillsons. Trans-Atlantic language differences.

The internal pressure of a service jack is around 30,000 PSI so that requires a great deal of torque to seal up. Keep up the good work.

In the case of my jack a calculation showed around 8,500 psi for max load.

There seem to be much better seals available than those fitted, it looks like most would require a different piston but that is almost a trivial thing to make. With your experience do you have any recommendations for a better seal type? I am thinking of a U seal with O-ring backup.

[tonyfoale]

I should have mentioned in my original post. that if anyone intends to follow my lead and hone a cylinder still attached to the base, that often there is a valve in the base which stands proud a little. To avoid wreaking that valve you need to ensure that you have a hard stop on the lower end of the hone stroke to prevent it bottoming on the base.

[nhengineer]

This is basically what I tried, but I got to the stage where I got concerned about breaking something. I had to google what a MF wrench was, it was what I tried but I am used to them being called Stillsons. Trans-Atlantic language differences..

I'm curious what GOOGLE thinks a "big MF pipe wrench" is. Around here (central NH, USA) the "F" part is an expletive and the "M" part stands for mother. It looks like this only the handle is 48" long.

Here's the WEB page. https://www.whitecap.com/shop/wc/p/r...iABEgICk_D_BwE

In the case of my jack a calculation showed around 8,500 psi for max load.

There seem to be much better seals available than those fitted, it looks like most would require a different piston but that is almost a trivial thing to make. With your experience do you have any recommendations for a better seal type? I am thinking of a U seal with O-ring backup.

Back 30 or so years ago I purchased my parts kits from The Jack Pack & Tool Company on N Marianna Ave, Los Angeles, CA. They are out of business - couldn't compete with $25 Chinese throwaways. Now, if it won't hold the weight, I put in a new ball check (from McMaster-Carr). The ram cup is usually not available but ram cups seldom are the problem anyway. The only other "seal" is the shaft wiper (and now-a-days that usually just a standard O-ring), the release needle valve housing and the pump ram (and they're usually just O-rings too). I've seen some jack rams with double or triple O-rings instead of a cup. That kind may NEVER give satisfactory results under max load after a bit of use and maybe not even when brand new.

Basically, if it won't hold the weight, it's the ball check and that's just a commercial steel ball bearing. If the ram cup is worn out, I trash the jack because, if it's worn out by spending its life in nice slippery hydraulic oil, it's seen a great deal of use and time to be retired. Same deal for the pump ram. The pressure is generated by the pump ram with a ball check usually on the far end of the chamber.

The gauge on my 20-ton press is maxed out at 40K psi. That's when the relief opens. Working pressure is red lined at 30K but I've occasionally loaded it up to 40K on special occasions. 8.5Kpsi should not be much of a challenge even for Chinese jack power units.

Does the ram creep back under load? That would most likely be the check valve. I'm glad to share what I know with you.

I hope I've helped somewhat. Get back to me if you need more information.

[love-horsepower]

Baum Hydraulics in Omaha has about any seal made and they are cheap. 800-228-9222 or 9288

[tonyfoale]

Baum Hydraulics in Omaha has about any seal made and they are cheap. 800-228-9222 or 9288

Thanks, I live on the other side of the pond and the cost of shipping small parts here is usually many times the value of the part.
For now I have no particular problem, it was just that I can rarely resist the temptation of improving stuff.

[nhengineer]

Baum Hydraulics in Omaha has about any seal made and they are cheap. 800-228-9222 or 9288

I always thought Baum was just cylinders & pumps. Thanks for the lead. However, I see nothing there regarding service jacks which is what we were discussing.