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Old 06/19/2017, 11:28 AM   #1
karimwassef
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Uni-seal rotation or linear action

I started using uni-seals last year and I'm very pleased with their flexibility. I realize that their primary function was to provide an alternative to bulkheads for rounded surfaces but I've found them excellent for flat surfaces too and I'm exploring more uses.

I find that while the fit is initially very tight, once in place, they can move in/out and rotate with some force applied. This doesn't seem to leak or even weaken them over time (so far).

I'm curious about going further and potentially actuating through a uni-seal as part of a system design. Basically, if I want to rotate a pipe end, stick it through a uniseal and rotate the dry side. The wet side moves without a leak...

Same with in/out translation motion.

Anyone done this?


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Old 06/19/2017, 12:22 PM   #2
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Not a good idea IMO..
I'd suspect the friction from the rotation will cause issues long term.. heating/wear..

But yes uniseals are good at what they do.. I'll use them in place of bulkheads too..


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Old 06/19/2017, 12:49 PM   #3
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The PVC is very resilient to wear. As is the rubber material. Looks like I need to set up a mattress-bounce test and see how many revolutions it takes to tear a leak in a uniseal? Maybe rotate a 1" under a foot of water at 120rpm as a baseline.

Of course, one seal could be different from another (defect rate, manufacturing tolerances)

Was really hoping someone had already done it and could say it's been working fine for 10 years.


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Old 06/19/2017, 01:19 PM   #4
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Of course frequency of movement/displacement/number of cycles,etc.. will come into effect..
Is it going to work for a limited number of cycles.. Sure..
But..
I certainly would not consider rubber nor PVC "very resilient to wear"...
If "wear" was one of my requirements then PVC/Rubber would not be in that list..

The coefficient of friction between both would be lousy..


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Old 06/19/2017, 02:16 PM   #5
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Sure. That's why it's a good seal...

But I can overcome it with a geared motor. I'm not looking for fast motion- slow deliberate and controlled is fine.


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Old 06/19/2017, 02:27 PM   #6
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Quote:
Originally Posted by karimwassef View Post
Sure. That's why it's a good seal...
And thats why its lousy at long term reliable "power transmission"..


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Old 06/19/2017, 03:50 PM   #7
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well... not necessarily. I'll give you an example - I've used PVC repair extenders for years as power transmission devices... double O-ring internal construction and free to move both rotationally and laterally.. The only problem is that they're very long (almost 12" in the case of the 2" extender).

I have a thread on here where I take it apart after a couple of years and the O-rings and seals are fine.

Trying to do the same with this given that it's essentially a zero-thickness version.


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Old 06/19/2017, 03:56 PM   #8
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http://www.reefcentral.com/forums/sh...inear+actuator

http://www.reefcentral.com/forums/sh...2229274&page=8

http://www.reefcentral.com/forums/sh...light=actuated

and this is the more recent one - trying to make it smaller

http://www.reefcentral.com/forums/sh...ctuator&page=2


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Old 06/19/2017, 04:01 PM   #9
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So any time you have movement and friction, you're going to have wear. The rubber in uniseals is fairly soft when compared to PVC, so it will likely wear first. How fast depends on how smooth or rough the other surface is among other things.

I've found silicone gasket lubricant makes inserting pipes through uniseals much easier. You could probably use it for your purpose as well.

To echo what others have said, you're using them in a capacity for which they weren't designed. The rate of wear and risk for leaks is completely unknown. At bare minimum I'd have a replacement schedule for them. If a leak has potentially serious consequences I'd look for other options. Or not if you like to live dangerously.


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Old 06/19/2017, 06:07 PM   #10
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O-rings are available in a variety of materials more suitable for what your trying to do. Although not ideal for rotational sealing. You could have some custom pieces made up with a couple of o-rings like the repair piece but shorter pretty inexpensively I would think. You could possibly modify schedule 80 bulkheads.
For that matter you could probably machine some schedule 80 bulkheads to take proper seals designed for rotating applications. One on each end of the bulkhead.


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Old 06/19/2017, 09:34 PM   #11
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Yeah, i would look into proper seals (like oil seals) designed for the job.

A uniseal should be tight to seal, once it wears some and the movement is good its no longer sealing...


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Old 06/19/2017, 10:04 PM   #12
karimwassef
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I can also measure the torque and use that as a warning alarm.

While the seal may fail, it may take years for it to do so - that's the variable I need to determine.

I had the same concerns with the o-rings in the repair extenders but I've empirically determined that they work (3 projects now running for three years). Need data.


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Old 06/20/2017, 05:59 AM   #13
der_wille_zur_macht
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Go for it. It may work better than expected. "Real" seals are designed the way they are mostly to reduce drag, the uniseal is going to have a lot of drag but I don't really think that automatically means it'll wear out quickly.

What are you trying to actuate, exactly?


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Old 06/20/2017, 08:13 AM   #14
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Several parts need to move.

One is a horizontal multi output return line that I'd like to rotate for 45 degrees up and down. I had a convoluted mechanism to get it to the right depth but this would be much simpler.

Another is a mid tank overflow box with three lines. The box can move up and down to simulate tides. I think I'll stick with the extenders on that one since the risk is too high


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