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john hobdeclipe
02-22-2008, 08:52 PM
The jack on my cherry picker doesn't do it's thing very well, so I decided to find out why. I took it apart, cleaned it as well as I know how, and decided that the problem is most likely the piston seal on the ram.

So, where can I fine parts for an old, no-name jack?

Here's what the seal looks like.

http://www.auldooly.com/imagehost/MVC-322F8.jpg
http://www.auldooly.com/imagehost/MVC-323F8.jpg
http://www.auldooly.com/imagehost/MVC-324F8.jpg

It's a plastic cup with an o-ring inside. I presume the o-ring is held in a shallow groove on the reduced diameter shank, and must be just the right size to keep some outward pressure on the plastic cup. Right?

Any idea where to find a replacement seal? The cylinder bore is 30mm.

I determined this to be the likely culprit, mainly because the lower 4 inches or so of the ram show some brownish discoloration, which I take to be from old dirty jack oil that leaked to the wrong side of the seal, and stayed there because the jack was never extended far enough to squirt the oil back into the reservoir. But I could be wrong.

I have no idea who the manufacturer is, or how old the jack is. And the company who's name appears on the engine hoist is no longer in business.

I'd really like to get this thing back together and working without spending much money, if you know what I mean.

Thanks.

Rookie machinist
02-22-2008, 09:09 PM
I have had good luck finding hydraulic seals at local hose and hydraulic suppliers. If you have a "hose man" or AFC hydraulic in your area bring them the seal and they can usually match it up. You can look in the yellow pages under "hydraulic hose" and call around to local shops they should be able to help you out.

sconisbee
02-22-2008, 09:10 PM
Try here for cup seals

http://www.mcmaster.com/nav/enter.asp?pagenum=3396

wierdscience
02-22-2008, 09:27 PM
Or you could do as I have done and turn one up out of glass filled teflon or polyurethane.It's not complicated at all,simply match the profile you have there and add a few thou to the OD of the contact lip.

I have done quite a few jacks and pallet truck cylinders this way when replacements were not availible.

If it's a common 8 or 12 ton engine hoist cylinder a new replacement can be had.Check HF,I think they have them for around $40 see here-

http://search.harborfreight.com/cpisearch/web/search.do?keyword=LONG+RAM+JACK&Submit=Go

john hobdeclipe
02-22-2008, 10:23 PM
Thanks.


Or you could do as I have done and turn one up out of glass filled teflon or polyurethane.It's not complicated at all,simply match the profile you have there and add a few thou to the OD of the contact lip.
That sounds easily doable...but I don't have any polyurethane here...what hardness should I look for? Any suggestions / advice for machining a piece that thin?

If it's a common 8 or 12 ton engine hoist cylinder a new replacement can be had.Check HF,I think they have them for around $40 see here-
Are these any good? Anyone have any experience with them? Mine is a common 8 ton long reach jack.



There was nothing on the McMaster - Carr page that looked to be close enough to work in a 30 mm (1.181") bore.

Should I go ahead and take a booger hook and pull that o-ring out? Anything going on here that is not obvious?

wierdscience
02-22-2008, 11:11 PM
Thanks.



There was nothing on the McMaster - Carr page that looked to be close enough to work in a 30 mm (1.181") bore.

Should I go ahead and take a booger hook and pull that o-ring out? Anything going on here that is not obvious?

I would be willing to bet the jack you have is either Taiwan or Chinese in origin.We sell both where I work and the only problems we have ever had were units that leaked oil out during shipping and customers who over tightened and scored the valve seat.There is also one model that is a double pumper meaning it has two pump pistons and delivers fluid on both up and down strokes of the handle.

That is a clear poly U-cup piston with an O-ring energiser.The O-ring holds the seal lip against the bore for a tighter seal,as the pressure increases it forces the O-ring to compress which in turn forces the lip tighter to the bore.

If you decide to try and make one you will need something in the 70-75 shore A scale hardness,that's a little harder than tire tread.Make it the same crossection as the original and use the same size O-ring for the energiser.

If yo either buy or make a seal be sure and run a fine bottle brush hone through the full length of the bore before reassembly.That will get rid of the score marks and burrs that probibly put the scuffs in he seal lip in the first place.

It's hard to find any off the self jack parts here unless it's a pallet truck.Most of the bottle,floor and hoist jacks are proprietary and once out of production impossible to find.

john hobdeclipe
02-26-2008, 09:40 AM
Or you could do as I have done and turn one up out of glass filled teflon or polyurethane.It's not complicated at all,simply match the profile you have there and add a few thou to the OD of the contact lip.


Will a new, yellow plastic hammer replacement tip be about the right material to make this with?

Scishopguy
02-26-2008, 03:54 PM
If you can't find a supplier and need it to work in a hurry you can always shim under the o ring with a little thin gasket material. As was said, you only need to make the o ring a few thou larger to compensate for wear. That is a desperation fix though. You should be able to get what you need from any good hydraulics supplier. My favorite source is Capitol Rubber. They are a nation wide company and have locations all over.

http://www.capitalrubberco.com/main_subset.htm

aboard_epsilon
02-26-2008, 04:19 PM
I'm fresh on this

discovered my ignorance of these things the other day

are you aware that you top up the oil through a bung half way up the ram ...

i wasn't and was continually taking bolt out with spring and loosing more oil than i was putting in ....i tried everything to get oil in through that bolt hole including inverting the thing ..(trolley jack )

topped up through the bung in the ram in the end ........and all function restored ....i had no idea .,who would have thought that ...i didn't ...till the end.

all the best...markj

davidh
02-26-2008, 07:03 PM
If you can't find a supplier and need it to work in a hurry you can always shim under the o ring with a little thin gasket material. As was said, you only need to make the o ring a few thou larger to compensate for wear.

in a pinch i have shimmed o-rings with teflon tape. just a few wraps and reinstall the seal or oring.

john hobdeclipe
03-07-2008, 10:10 PM
Well, guys, I decided not to waste any more time trying to find a seal for this jack. I called several places that I found either via google or the yahoo yellow pages. No luck finding a 30mm piston cup seal.

So I took a yellow Stanley plastic hammer tip (a new one) and started playing with turning it on the lathe. And on the second attempt, I got a seal that works.

Of course, I don't know how long it will last, but for now it will take all the pressure I care to test it with, and it doesn't leak, so I'm happy with it.

Now I can use the cherry picker to start disassembling my Delta Toolmaker, so I can clean it up and get it running, so I can use it to sharpen the knives for my woodworking jointer, so I can use that on a project to make a cabinet to organize my mill cutters and lathe tools, so I can.....