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Author Topic: Carl Shoup Syringe o-ring  (Read 1149 times)

Offline Brett Buck

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Carl Shoup Syringe o-ring
« on: May 30, 2019, 04:41:26 PM »
One of my many amateur-hour moments at the Northwest Regionals was that I dumped an entire syringe of fuel on the ground when the plunger pulled out. The reason is that the o-ring finally gave way, suddenly reducing the back-pressure. The ring ended in 3 peices on the ground, along with 5 ounces of fuel.

    For anyone wanting to replace the ring, I found the correct size and have some candidate sources for replacements. The ring is dash number 125 - nominal 1.5" OD with a 3/32 cross section. I got replacements this size and they fit perfectly. I chose "soft Viton" material from McMaster-Carr:


https://www.mcmaster.com/o-rings
Chemical-Resistant Soft Viton® Fluoroelastomer O-Rings

   These are chemical-resistant and very soft. Perhaps too soft, they tend to flow out of the grooves a bit and stick. We will see how they last, but it works now. I think you want these more than you want the black Buna-N or neoprene types, because they shouldn't degenerate due to exposure. The original red ones were silicone, and you can get those easily, too.

     Note that the same O-rings will NOT fit the Jim Lee plunger, I think they are the same OD but 1/8 cross section - probably dash number 218, but of course you can get them from Jim. Little hard to get in touch with Carl these days, unfortunately.

    Brett
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Offline FLOYD CARTER

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Re: Carl Shoup Syringe o-ring
« Reply #1 on: May 30, 2019, 09:15:59 PM »
Jim Lee provides a machined top plate for his syringes, along with a machined plunger and O-ring disc.  The plunger can't get out.  His O rings stand up to glo gasoline and diesel fuel!  I've tried them all.

I made the mistake of getting a glass syringe to use as a primer.  Bad idea!
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Offline Brett Buck

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Re: Carl Shoup Syringe o-ring
« Reply #2 on: June 01, 2019, 04:10:07 PM »
Quote from: Motorman on June 01, 2019, 12:54:16 PM
I use the optional black Buna-N  O-ring in my Carl Shoup plunger. Works with any type of fuel and I've never had one deteriorate. Now I see they make soft Buna-N, might have to try that. I also glue the tip on the plunger with JB weld as I've had the handle pop out from the tip. I try to keep it out of the sun because the plastic body will shrink and get tight to push/pull. Maybe I'll try boiling water next time this happens.

      I strongly suggest you replace the Buna-N version with the red silicone, or something else (like the Viton). The black ones will definitely degenerate and release something into the fuel eventually. It;s much better than the stock all-rubber plunger, just because its smaller and has less surface area.

    Brett
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Offline Brett Buck

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Re: Carl Shoup Syringe o-ring
« Reply #3 on: August 17, 2019, 12:21:42 AM »
As a follow-up, the white, very soft, Viton, o-ring seals very well, and runs very smoothly when you are using it, but, it is so compliant that it tends to push the oil out of the interface between the plastic and the o-ring, and it then wants to stick like a rubber tire. You can always pop it loose, but the first action of the day and it is usually stuck.

    I reverted to the medium durometer silicone, and that doesn't have quite the same issue. The harder Viton is also fine. All are completely impervious to model fuel, as far as I can tell.

    I now have a very large number of acceptable Carl Shoup o-rings that can be used as replacements, that is, 3/32" cross-section -125 sized rings. If someone wants them I will have them with me at contests, or, send me a SASE and I will send you a couple for free, until I run out.

     Brett
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Offline RandySmith

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Re: Carl Shoup Syringe o-ring
« Reply #4 on: August 19, 2019, 01:06:25 PM »
The best material  I have found for this is  the  RED  silicone  O rings,  and  as  Brett  stated  it will  turn to goo  after time, and it will also  flat spot and  stick  top the  syringe  sides

Randy
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