Is it possible to convert hydraulic bottle jack to pull rather than push?

[auswelder]

Hi all,

Just wondering if it would be possible to convert a typical automotive type bottle jack to pull rather than push?

I've never seen it done before. I know you can buy the pull back type rams with the external hand pump but am after something with the pump integrated with the cylinder.


Anyone seen this done before?


Thanks

[NortonDommi]

Interesting. It may be possible depending on the jack. You would need to reverse the seal and plug the existing high pressure inlet, divert it to what is the standard topside plus uprate the seal.
Probably be just as easy to build a new double acting cylinder and cut the pump off an old bottle jack with a diverter valve in the high pressure line to change direction.

Would be very handy, I can think of multiple occasions when I would have liked one.

[auswelder]

Being able to change directions both ways would be really handy, don't know how i'd go about making up a new cylinder though.

[hemmjo]

Typically, the ram on a bottle jack is almost the same diameter as the cylinder. Even if you could get the seals , valves and plumbing worked out, you would not generate much force on the return stroke.

[tonyfoale]

No you cannot pull instead of push. I posted a couple of threads on here about turning bottle jacks upside down. In one of those posts there is a drawing showing what is inside that kind of jack, as Hemmjo said the piston and cylinder are near the same diameter so the only way to produce a force from the pressure is to apply the pressure to the end of the piston, as one end is external you can only do this to the pushing end.
There is way to cheat though but it requires a silly amount of messing about and is not really practical.
If you drill a centre hole in the base, you could put a small rod through it and screw it into the main ram. The larger the diameter that you make the rod the less will be the force on it because it will take area away that the pressure cannot act on. Of course you have to fit a high pressure seal to prevent oil loss.
Even if you did it, you could only use it to pull upwards unless you made other modifications to allow the jack to work at any angle.

Here is the pic that I mentioned, click it for full size.

[Pjcde59]

[QUOTE=auswelder;157574]Hi all,

Just wondering if it would be possible to convert a typical automotive type bottle jack to pull rather than push?

I've never seen it done before. I know you can buy the pull back type rams with the external hand pump but am after something with the pump integrated with the cylinder.


Anyone seen this done before?

Yes. Anchor the cylinder and attached pulling arm to the bottom of the jack. What you activate it the body of the jack will push downward with the attached arm. Hence pulling instead of pushing

[Crusty]

It can be done with cage attachments. There is a two legged lower cage under the base and the legs extend upward past the end of the ram to an attachment point. There is also an upper two legged cage whose legs extend downward from the ram past the base to another attachment point. The two cages are turned 90º from each other so that they can pass by each other as the ram extends. The legs must be long enough for full jack extension before coming together to form the attachment points.

[mr herb]

The jack itself must always remain with the pump at, or near, the bottom, or it will run out of oil. The more out of vertical, the less total stroke unless the pump is at the bottom