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Repairing a cheap Ducato jack

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Andrew Tinsley13/09/2017 16:20:11
469 forum posts

I have a couple of these, that don't work. I have stripped them down and it is the Nylon / ptfe "piston" that has failed. This is simply a piece of round bar material partially bored through and a suitable hole for the retaining bolt. The other end has a slight flair to produce the seal.

Now I can replicate the Nylon / ptfe arrangement. But as all these jacks seem to fail in this mode. I wondered if a metal piston and maybe a couple of good quality O rings might be a better bet. Or whatever the hydraulic people use for seals. I don't know much about that side of things.

Now I suspect that most people would simply bin them.However having got them apart I might as well effect a safe repair, whatever that may be. Any suggestions, including binning them?

Andrew.

mark costello 113/09/2017 17:47:19
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350 forum posts
2 photos

Could You contact a local hydraulic repair shop for off the shelf parts. Much safer, although I am not afraid to try and save some cash, in this instance I would try a shop first.

Andrew Tinsley13/09/2017 22:33:45
469 forum posts

I would certainly do that, but no one has spares for these jacks, I think they are regarded as a throw away item!

I was considering using a high quality Viton O ring in a metal version of the PTFE / Nylon "piston" As for safety, I expect such a set up would be safer than the original seal!

Andrew

tractionengine4214/09/2017 06:59:05
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319 forum posts
76 photos

Hi Andrew

You can download an o ring guide here **LINK**

You can determine the pressure that the seal has to take by Jack max load / piston area.

The clearance between the piston and cylinder is termed the extrusion gap, this should be within specified limits for the seal to function reliably. If the extrusion gap is to big for the pressure applied the seal could extrude through the gap. My guess is your application is low pressure though.

A quality 70 shore hardness o ring will easily take more more than 1000 psi. Backup rings are used for higher pressures, these effectively increase resistance to seal extrusion.

I think using an o ring will provide a much safer and reliable jack. If the cylinder is steel then a bronze piston would be preferable. The finish on the cylinder bore needs to be a smooth finish with no scoring.

Nige

PS presumably you will need to put a seal between a metal piston and the piston rod.

Edited By tractionengine42 on 14/09/2017 07:24:07

Ady114/09/2017 08:11:41
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2860 forum posts
369 photos

The crappy bit may also be a safety factor, so you can't jack up something too heavy

Andrew Tinsley14/09/2017 11:59:48
469 forum posts

Thanks gentlemen, very good advice! A couple of bronze "pistons" would probably cost quite a bit. Maybe Brass could be used.

I am aware of the likely problem with sealing the area where the nut holds down the Nylon /ptfe "piston. I have not yet had this apart to see how it is done on the original "piston" I suspect it isn't a smart solution. So maybe I need to put on the thinking cap, but not a huge problem I suspect.

Thanks again,

Andrew.

Geoff Perkins 115/09/2017 00:55:26
108 forum posts
12 photos

I've got a cast iron bottle jack (square thread telescoping shaft type) which would at least 60 years old by now, it still works fine, and will lift any vehicle i own. Beats any of those hydraulic things wink.

Don't know what i'd do if it ever breaks, though!! indecision

Andrew Tinsley15/09/2017 11:57:48
469 forum posts

Strangely enough, these jacks appear to be very well made. I am sure they would last a very long time if it were not for the nasty plastic "piston". Maybe Ady is correct and it is a built in fail device to prevent overloading!!!!!!!!! Thanks Nige for the reference on O rings. That will come in handy. I used to make and assemble high vacuum equipment.

So I know a bit about o rings, but not for hydraulic application. I would have gone blithely along and sized everything for high vacuum application. Glad you put me right!

Thanks everyone!

Andrew.

donkey15/09/2017 12:44:52
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51 forum posts
5 photos

not sure an o ring is the answer. a wiper seal lets the oil act on the wiper area allowing a greater effective seal.maybe one could be incorparated in to your design.

bri

Andrew Tinsley15/09/2017 13:39:00
469 forum posts

Now that is interesting. Do you know where I can look up details of wiper seals, I have never heard of them!

Thanks,

Andrew.

donkey15/09/2017 14:30:04
avatar
51 forum posts
5 photos

just google wiper seals for info.

bri

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