U cup seal selection

[B_Bimmer]

I need this seal for a press and am having a much harder time finding it than I was expecting. Most seem to be much shorter with even close to the same ID and OD. Am I missing something?

 

[jacked_72]

You might try measuring in mm and seeing if there isn't a better selection. Good luck.

 

[Blt2Lst]

I was able to source a metric u cup seal on ebay for a jack I was rebuilding, might try there.

 

[B_Bimmer]

Metric seemed even more random initially, and not as available, but I'll see if that doesn't help.

 

[bob15]

Try measuring the OD with a micrometer. Dial calipers aren't the best choice for what you are doing/measuring; a micrometer is the correct and more accurate tool/instrument.

 

[matt_i]

It does seem like its way out of the range of U cups and "loaded" polypaks that you can buy off the shelf.

You didnt ask but machining a new piston wouldn't be out of the question. Looks like a 1" OD requires a 3/4" ID and a shorter groove width.

Does the cylinder's endcap have any interaction with the seal to change the sealing diameter? It seems odd to me that the end of the rod is mushroomed over on its end, is that a part which contacts workpieces?

 

[B_Bimmer]

It is a relatively simple part, making a new one that fits standard parts may very well be the best long-term solution. I was just hoping there was a better source I had not yet stumbled upon.

 

[B_Bimmer]

I was able to source a metric u cup seal on ebay for a jack I was rebuilding, might try there.

Good call, many more options on the metric side. Nothing perfect, but closer. Now the question is will I be happier with one 15mm ID 25mm OD 8mm height or one 14mm ID 24mm OD 8mm hight...

 

[metlmunchr]

I wouldn't put much faith in those calipers. Your .98" would be 24.89 mm yet when you switch to metric you're getting 24.7 mm. 0.2 mm difference on the same bore, or ~.008" difference. That's getting into stick rule accuracy and definitely not accurate enough to determine what seals you need.

FWIW, I picked up a digital caliper at HF a while back on sale for $9.99 just to leave in my garage at home for checking stuff without bringing my good stuff home from my shop. It seemed like it was more decent than what I'd expected for the price, so I checked it at a dozen various places with gage blocks (accurate to .00005") and the caliper was dead on at about half the measurements and within .001" on the remainder. On the order of 8X more accurate than what you're using, and dirt cheap at ten bucks.

 

[Indexmill]

Try measuring the OD with a micrometer. Dial calipers aren't the best choice for what you are doing/measuring; a micrometer is the correct and more accurate tool/instrument.

Nonsense. That digital caliper is fine for that job assuming he knows how to use it.

 

[B_Bimmer]

First of all, I appreciate all of your thoughts and opinions, but this is a chinese pump and ram on a US built frame, and I doubt the manufacturer bothered with tools that were all that precise in it's manufacture. A few hundredths isn't going to change the world with this thing. In the end none of the available seals are as deep as the original, so whatever I try will not be "right". Stuff in the real world rarely is. I was just curious if anybody had any actual experience with something similar and could offer some practical advise. A few of you did, and a few of you threw in overcomplicated thoughts that one would normally get at a bar, local gas station, or garage. It's all good and I appreciate it all.

Now my problem is with the approximately 10mm necked down area on the piston where the seal sits. Since it appears all the seals close to mine are only 8mm high, do you think if I filled the gap below with an o-ring it would keep the u cup from sliding back and forth giving me a "dead spot" in every stroke of the piston?

 

[bob15]

Nonsense. That digital caliper is fine for that job assuming he knows how to use it.

Not nonsense, but rather truth. You measure round objects more accurately with a micrometer, both OD & ID. There is a reason why you will find micrometers by lathes.

 

[Daveyclimber]

In my experience metric u cups are almost always exclusively used in modern equipment. All hydraulic equipment i have ever repaired with the exception of ORB and ORFS orings were all metric.

 

[OccupantRJ]

Try sending your pictures to the O ring store.
https://www.theoringstore.com

 

[Wrench97]

Sometimes you can double them up and add a packer or two.

 

[paulsomlo]

Try measuring the OD with a micrometer. Dial calipers aren't the best choice for what you are doing/measuring; a micrometer is the correct and more accurate tool/instrument.

Calipers are fine for this application - the seals are spec'd as "nominal" dimensions anyway - it's a piece of flexible plastic; I wouldn't be surprised if they vary +/- 0.005". Measuring the rod OD where the seal sits and the cylinder ID is sufficient to specify the seal.

Does the cylinder's endcap have any interaction with the seal to change the sealing diameter? It seems odd to me that the end of the rod is mushroomed over on its end, is that a part which contacts workpieces?

That's for retention of the seal - it's the cheapest way of doing it.

Now my problem is with the approximately 10mm necked down area on the piston where the seal sits. Since it appears all the seals close to mine are only 8mm high, do you think if I filled the gap below with an o-ring it would keep the u cup from sliding back and forth giving me a "dead spot" in every stroke of the piston?

I think that's a good solution, although I'm thinking that for a fixed ID/OD, the taller seal will have greater load capacity. But for your application, it may not matter. Do try to leave a small space for the seal to expand, heightwise. Both temperature and exposure to hydraulic fluid will cause that to happen. I can't remember the guideline, but maybe 10% of the seal's height.