Floor jacks and hydraulic seal types

[joeswamp]

This post is really directed at HiBall, but other jack experts please chime in.

OK so like everyone else on here I've learned a whole lot about floor jacks from all the recent discussions. However one thing I'm still confused about is floor jack seal design. It sounds like the "universal cheap import" jacks use O-ring seals (which fail quickly), whereas the good jacks use cup seals or something more substantial.

So for example, the AFF 200T:

is an example of a cheap import jack. We see on its part breakdown:

http://www.affjaxx.com/parts_docs/200T.pdf

That the ram is sealed by parts H3 and H4 (an o-ring and "o-ring returner"). I believe the o-ring returner is the part HiBall says not to mess up when you attempt to rebuild the jack, as they're hard to find.

Another Chinese jack, the $200 Norco 71232:

seems to use different seals on the ram. According to the part breakdown:

http://www.norcoind.com/norco/downloads/exploded/71232_Exploded.pdf

parts 80 and 81 (a u-cup seal and back-up ring) seal the ram. This would be a good seal design right? Norco's are Chinese but not made by Shinn-Fu I believe.

Finally, we look at a high quality floor jack, the Made in USA Milwaukee Model 40:

Here's the crazy part, if we look at the parts breakdown:

http://www.milwaukeehydraulic.com/model40.pdf

The ram is sealed by parts 68 and 69 (an o-ring(!) and 2 backup washers).

So what's the deal here? If o-rings are really that bad, why does Milwaukee use them? Or is it the Shinn-fu hydraulic unit design and/or quality that's the real issue here? What about Chinese jacks that use u-cup seals?

 

[Hiball]

Ok. I finally got some puter time. In reference to the 3 models you listed here, First off the Low Profile jack. It does use the Junk Ucup retainer with the Oring similar to the one in my tutorial and this Pic.



These are very poor design and the oring isnt used as a sealing surface, It is in fact used as a loaded ucup and the pressure from the fluid uses the oring to keep the pressure uniform around the very thin Ucup retainer.

The Norco jack in the picture is your typical Import design that has been used for many years. That jack actually uses Poly Ucup so i will vouch for that part of the jack. I still dont think its worth the money when compared to the HW models but is hands down better than the Previously discussed Oring/Ucup retainer. You can find actual Ucups in the older Imports including the legendary Green/White Sears Jap jacks.

Now for the million dollar question. The Milwaukee jack does utilize oring on both Pumps and the Ram, But the main difference is how they are used. Instead of being inside a U cup retainer (see pic above) its used as a compete sealing surface where it gets a 360 degree seal inside the Ram. This is a very good design and im sure a few of you have torn hydraulic cylinders down where the same design is used. When you consider the tight tolerances that are used it works very well, Not to mention there is a backup on each side of the Oring, which is like injecting a Oring with steroids. I cant really vouch for Milwaukee jacks, Ive probably only worked on 2-3 in the 20 years ive been rebuilding jacks. There not near as common as a Walker/Lincoln design despite there History.

 

[joeswamp]

OK now I get it, thanks so much for the explanation.

So the modern cheap imports use this super thin ucup seal and the o-ring is used to preload it against the cylinder wall -- I believe this type of seal is called a "loaded lip seal" and is a more modern design than the traditional u-cup. In your rebuild tutorial you say that the thin o-ring retainers (the actual sealing part) usually don't go bad -- I would have expected those to fail first, rather than the o-ring. How do these modern import jacks typically fail?

Interesting that Milwaukee uses o-rings the way it does, this must be a really old design. I'm surprised it works as well as it does -- it probably requires tighter tolerances and finishes on the piston and cylinder, and I'd bet that's one of the reasons this jack is pricey.

Thanks again.

 

[Hiball]

OK now I get it, thanks so much for the explanation.

So the modern cheap imports use this super thin ucup seal and the o-ring is used to preload it against the cylinder wall -- I believe this type of seal is called a "loaded lip seal" and is a more modern design than the traditional u-cup. In your rebuild tutorial you say that the thin o-ring retainers (the actual sealing part) usually don't go bad -- I would have expected those to fail first, rather than the o-ring. How do these modern import jacks typically fail?.

Yes, you are correct a actual Ucup with a solid U-portion is called a Loaded Ucup. I wouldnt classify these Ucup sleeves with a Oring insert as a "Loaded U cup" but without a doubt thats how there being used. The reason they fail is because this design relies on the Oring being flexible enough to keep the very thin sealing surface uniform inside the cylinder upon Pressure entry, When they harden they lose that trait. When that happens you get Oil bypass, the jack seaps and oil bypass on the tank nut account its not designed to keep that amount of oil back.

 

[joeswamp]

OK I researched this a bit more and the type of seal on the modern Chinese jacks seems to be called a "piston cup" seal. However it's being used in an unusual fashion; after looking at lots of catalogs I can't find an example of one being loaded or energized with an o-ring. Usually the bottom part of the seal has more relative area and it's clamped between two pieces, like this:

According to one manufacturer, the very thin wall version of these seals have an advantage because they're so flexible -- they seal over a wide range of pressures and don't initially leak before pressure is built up. I suspect these seals allow Shinn Fu to build their cylinders with sloppier tolerances, which work until the o-rings harden up.

Weird that I can't find an example of an "o-ring inside a piston cup seal" from a mainstream manufacturer though, and it definitely looks like getting one of these from a normal hydraulics supplier might be difficult.

 

[Hiball]

OK I researched this a bit more and the type of seal on the modern Chinese jacks seems to be called a "piston cup" seal. However it's being used in an unusual fashion; after looking at lots of catalogs I can't find an example of one being loaded or energized with an o-ring. Usually the bottom part of the seal has more relative area and it's clamped between two pieces, like this:

According to one manufacturer, the very thin wall version of these seals have an advantage because they're so flexible -- they seal over a wide range of pressures and don't initially leak before pressure is built up. I suspect these seals allow Shinn Fu to build their cylinders with sloppier tolerances, which work until the o-rings harden up.

Weird that I can't find an example of an "o-ring inside a piston cup seal" from a mainstream manufacturer though, and it definitely looks like getting one of these from a normal hydraulics supplier might be difficult.

The reason you cant find a "Oring inside a piston cup seal" is because they are hard to find and have a short life span. Here is some examples of some more piston cup seals along with a standard Ucup and a loaded Ucup. The most common type of Piston cup used in hydraulic jacks are leather cups, Here is a variety of them and they sit over a stem and get fastened with a washer and nut.

Next you have your standard Ucup.

Now the loaded Ucup.

And now you have the Import special.

Which one do you want in your Jack?

Those are all versions that are used in a Piston sealing sitsuation, The opposite of Piston seals are gonna be your rod seal. You will find these on most of your Import jacks where the seal is inside the hydraulic unit and the rod floats inside of the seal like this.

Hope this explains things for you.

Steven

 

[joeswamp]

Such great info (and not the easiest info to find either). I'll bet those leather piston cups pre-date the invention of the o-ring.

Thanks so much for taking the time to explain all this stuff.

 

[Hiball]

Such great info (and not the easiest info to find either). I'll bet those leather piston cups pre-date the invention of the o-ring.

Thanks so much for taking the time to explain all this stuff.

The Leather Piston cups are still used in alot of todays hydraulic equipment but they are quickly being replaced by Ucups and definitely pre-date orings.

Steven

 

[Jan Greeff]

Can someone please help? I have a 45-year old trolley jack originating in Sweden and would like to replace the worn and hardened leather cup seal with a new, efficient seal. The cylinder is 32mm dia, the old seal is 10mm wide and has a 6mm mounting hole.

 

[tcianci]

Cool thread guys! I have a majorly old AUSCO long frame jack that I remember my father getting from a friend about 45 years ago. He made some new parts for it and I recall the leather cup seal soaking in neatsfoot oil or jack oil for along time before it was supple enough to reuse. I finally stopped using that jack about 10 years ago because it would weep around the ram when left sitting. I bought a kit for it back then but have yet to overhaul it. Hopefully HiBall won't mind if I ask some questions when I tear it down. I was told the jack was from the 1930's.

 

[HCRCnow]

Some more explanation on seals. Look at the U seal, this is a drawing of "Loaded U cup seal" without the Oring it is a U cup seal. Loaded U cups come with Orings and Quad rings.
http://www.hcrcnow.com/how-to-measure-seals.php

 

[HCRCnow]

Can someone please help? I have a 45-year old trolley jack originating in Sweden and would like to replace the worn and hardened leather cup seal with a new, efficient seal. The cylinder is 32mm dia, the old seal is 10mm wide and has a 6mm mounting hole.

Piston cups are available, I have only seen them in Standard not metric. Also they come in rubber(Buna) or fabric. Leather are available, but I can not find them 1 at a time. The closest to the size you need is, 1-1/4"OD with a 1/2" Lip and the center hole you have to make. If this will work, let me know.

 

[Hiball]

Can someone please help? I have a 45-year old trolley jack originating in Sweden and would like to replace the worn and hardened leather cup seal with a new, efficient seal. The cylinder is 32mm dia, the old seal is 10mm wide and has a 6mm mounting hole.

A Properly installed Leather Seal will give you Many Years worth of Service. Do you have a Model Number? I have lots of useless data for Jacks from that Era, Including OEM sizes.

 

[roar35]

I have a Astroline AM200F 2 ton floor jack that I believe needs new seals. All of a sudden stopped working. Anyone know where I can find these? Thanks

 

[chin00kie]

Wonderful thread. It has helped me to understand my jack. I need the "U cup" for the ram on my jack. Where is the best place to find a replacement. There is no name on my jack so I will have to go by measurements. I cannot find one locally.

 

[123Go]

Hey guys what happen to the pics that where posted here? I went to send this to a friend so he could see the different seals and no pics anymore?
Anyone have these pics so they can be reloaded? This was a great help so I hope it can be restored?
Thanks

 

[HCRCnow]

I have a Astroline AM200F 2 ton floor jack that I believe needs new seals. All of a sudden stopped working. Anyone know where I can find these? Thanks

Link to seal kit.
http://www.hcrcnow.com/shop/seal-kits/astroline/3176

 

[HCRCnow]

Wonderful thread. It has helped me to understand my jack. I need the "U cup" for the ram on my jack. Where is the best place to find a replacement. There is no name on my jack so I will have to go by measurements. I cannot find one locally.

PM sent

 

[HCRCnow]

Can someone please help? I have a 45-year old trolley jack originating in Sweden and would like to replace the worn and hardened leather cup seal with a new, efficient seal. The cylinder is 32mm dia, the old seal is 10mm wide and has a 6mm mounting hole.

PM sent

 

[123Go]

Pics never did come back on this site I see.
Shame as it was so nice to have them available. Guess they got hijacked?

 

[agradetools.com]

Ok. I finally got some puter time. In reference to the 3 models you listed here, First off the Low Profile jack. It does use the Junk Ucup retainer with the Oring similar to the one in my tutorial and this Pic.



These are very poor design and the oring isnt used as a sealing surface, It is in fact used as a loaded ucup and the pressure from the fluid uses the oring to keep the pressure uniform around the very thin Ucup retainer.

The Norco jack in the picture is your typical Import design that has been used for many years. That jack actually uses Poly Ucup so i will vouch for that part of the jack. I still dont think its worth the money when compared to the HW models but is hands down better than the Previously discussed Oring/Ucup retainer. You can find actual Ucups in the older Imports including the legendary Green/White Sears Jap jacks.

Now for the million dollar question. The Milwaukee jack does utilize oring on both Pumps and the Ram, But the main difference is how they are used. Instead of being inside a U cup retainer (see pic above) its used as a compete sealing surface where it gets a 360 degree seal inside the Ram. This is a very good design and im sure a few of you have torn hydraulic cylinders down where the same design is used. When you consider the tight tolerances that are used it works very well, Not to mention there is a backup on each side of the Oring, which is like injecting a Oring with steroids. I cant really vouch for Milwaukee jacks, Ive probably only worked on 2-3 in the 20 years ive been rebuilding jacks. There not near as common as a Walker/Lincoln design despite there History.

Hey I am trying to understand this subject and recommend good high quality jacks for my website. Would you be available to help me explain this in an easy fashion for people and give high-quality recommendations for floor jacks?