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Question about u-cup seals

need a little help

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#1 Gregory Lachowsky

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Posted 14 October 2013 - 12:53 PM

I am making a NFR and want to use a u-cup seal. What size would I need and how would I attach it to the plunger rod?
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#2 cheerios

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Posted 14 October 2013 - 08:58 PM

I'm not familiar with the acronym NFR could you clarify.
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22:46- jakejagan :Ryan, did you hear that Zeke's BBBB made N9 bleed?
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#3 CoolpantsMcgee

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Posted 14 October 2013 - 09:09 PM

I'm not familiar with the acronym NFR could you clarify.

Nitefinder rifle my good man.
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#4 cheerios

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Posted 14 October 2013 - 09:17 PM

Nitefinder rifle my good man.


Interesting, I've never heard it called that. 9691K53 should work for a seal.

Edited by cheerios, 14 October 2013 - 09:17 PM.

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22:46- jakejagan :Ryan, did you hear that Zeke's BBBB made N9 bleed?
22:47- Zorn :BONUS

#5 Gregory Lachowsky

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Posted 15 October 2013 - 07:32 AM

How would I attach it to the nylon plunger rod.
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#6 CoolpantsMcgee

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Posted 15 October 2013 - 09:39 AM

The screw that acnerfshop tells you to use in their video tutorial.
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#7 Gregory Lachowsky

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Posted 15 October 2013 - 12:15 PM

so u use the stock plunger head and just but the ucup on it
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#8 CoolpantsMcgee

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Posted 15 October 2013 - 01:24 PM

so u use the stock plunger head and just but the ucup on it

You doubleposted and no. You should be able to make the plunger head with washers and the seal sandwiche'd inbetween.
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#9 Gregory Lachowsky

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Posted 15 October 2013 - 01:26 PM

Kinda confused here
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#10 Drev

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Posted 15 October 2013 - 01:52 PM

If you don't know how to use a u-cup as a seal, you should just use the stock plunger head. However, if you really want to use a u-cup, look at how T da B attaches his u-cup to a plunger rod here.
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#11 T da B

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Posted 15 October 2013 - 03:15 PM

I fear you may be screwed, Gregory. Assuming that you're using 1'' OD tubing with a 1/16'' wall, 9691K52 and 9691K53 will be too fat and 9691K51 will be too small.

~T
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#12 Drev

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Posted 15 October 2013 - 07:39 PM

I would just use the stock plunger head for this one. You can even get a pretty good seal with it if you try hard. As for attaching it, drill into your plunger rod, tap it for a 6-32 screw, and screw on the plunger head with a 3/4" or 1" 6-32 screw.
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#13 Draconis

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Posted 15 October 2013 - 08:46 PM

I fear you may be screwed, Gregory. Assuming that you're using 1'' OD tubing with a 1/16'' wall, 9691K52 and 9691K53 will be too fat and 9691K51 will be too small.




Has anyone actually used a 9691K51? With the catalog specifying the OD of the base as 3/4, I'll bet it would fit the 7/8" ID tube. I mean, based on the OD difference between the lip and the base of the K52 (I have some), it seems reasonable. If you are not using the 7/8" ID tube, you could use the 1" Lee's tubing, which has an ID of 0.9" and would be perfect with the K52.
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#14 T da B

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Posted 16 October 2013 - 03:14 AM

I have not tried it, but here's my experience: I tried the 1 1/2'' OD U-cup in 1 1/2'' PVC (~1.6'' ID) and the difference of .1'' was enough to make the U-cup require tweaking to seal properly. The K51 U-cup has a 3/4'' (.75'') OD, and we're trying to fit it into a 7/8'' (.875'') ID. In this case: .875'' - .75'' = .125'' > .1'' so I'm pretty confident it will be too small. Basically, the ID of your plunger tube has to be barely bigger than the OD of the U-cup--I'd say around 1/16''. I came to this number by measuring how far the lip of the U-cup juts out from the Mcmaster OD. In this case it's a little more than 1/32''. There's definitely a lot less wiggle room than a washer sandwich, and I've found that none of the sizes are really compatible with any of our commonly used pipes :(
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#15 Drev

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Posted 16 October 2013 - 03:54 PM

I've found that none of the sizes are really compatible with any of our commonly used pipes :(

In Zorn's FAL 3, he uses a 9691K56 with 1.25" PVC. I haven't tried it myself yet, but I assume that it works considering he has a functioning blaster. It is good to know that this works even though it may be the only u-cup to fit a common pipe.
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#16 Gregory Lachowsky

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Posted 16 October 2013 - 04:03 PM

I would just use the stock plunger head for this one. You can even get a pretty good seal with it if you try hard. As for attaching it, drill into your plunger rod, tap it for a 6-32 screw, and screw on the plunger head with a 3/4" or 1" 6-32 screw.

Thanks for he help the reason I wanted to use a u cup is because I wanted to get a PERFECT seal not 98%. Thanks for the help
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#17 Zorns Lemma

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Posted 16 October 2013 - 06:56 PM

Thanks for he help the reason I wanted to use a u cup is because I wanted to get a PERFECT seal not 98%. Thanks for the help

You're not going to get perfect seal by that definition.

The best you can hope for as a generic test is that the seal is good enough that static friction overcomes plunger pressure when you plug the front. But you can achieve that without a u-cup
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#18 Daniel Beaver

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Posted 16 October 2013 - 10:02 PM

Perfect seals are overrated. Low friction is way more important.
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