Poly port size vs strength?

[sholo]

I'm re-working my Disco valve for my 2560 project and plan on using a teflon TP. Would a 1/4" OD x 3/16"ID (.031" sidewall) be sufficient enough to run 1850 psi, or should I go with 5/16" OD (.062" sidewall)?

Reason I ask is that although I will if need be, if I don't have to drill my tube out to .312" to accept a 5/16" TP, all the better! That, plus the fact I don't have any 5/16" Teflon rod at the moment or a 5/16" end mill either for that matter...

That being said, I want to do this right and only tear the gun down once in the process, so if 1/4" won't cut it then a shopping I will go!

Thanks for any insight you can offer!

[rsterne]

Usually, the transfer port is completely surrounded by metal.... the tube at the valve end, the breech in the middle, and the barrel at the top.... Therefore, it can't "expand" so the only issue is whether or not you can get a seal on both ends (against the valve and barrel) with a 1/32" wall.... It's marginaly, but will usually work if you get the length just right.... I find that about 0.010" of lengthwise crush usually seals well without risking collapsing the wall into the airflow path.... The transfer port in my .30 cal Disco Double is 5/16" OD with a 0.219" hole (0.047" wall) and is no problem at all.... Most "poly port" icemaker tubing is 1/4" OD x 0.166" ID (0.042" wall) and that also works OK.... I had one piece of poly tubing that was 1/4" OD x 3/16" ID and you had to get the length perfect but it did work, so what you are trying to do is not impossible.... I'd give it a try, for sure....

Bob

[Doc Sharptail]

Standard 1/4" o.d. x 3/16" i.d. poly ice maker tubing holds up well even to 3 K psi, as long as the end cuts are square, and the length right...

I usually cut mine with a 3/16" drill inside the tubing, with a small plumber's tubing cutter. This seems to get the square ends required.

That being said, I'm not really a fan of poly tubing~ especially on a gun that is going to see a lot of dis/re-assembly that good tuning seems to require. I still like the metal t.p. of the xx systems, and stay with it as much as possible. They are not that easy to drill out for expansion, but their longetivity is well worth the careful approach to expanding them.

Regards,

Doc Sharptail

[rsterne]

I have only seen 1 piece of poly tubing that was 3/16" ID, virtually all of it is 0.162- 0.166" ID, and you can drill a Crosman port to 0.162" so there is no advantage to the poly port, especially in .22 cal since you can't drill the barrel that big anyway....

Bob

[Doc Sharptail]

I have only seen 1 piece of poly tubing that was 3/16" ID, virtually all of it is 0.162- 0.166" ID, and you can drill a Crosman port to 0.162" so there is no advantage to the poly port, especially in .22 cal since you can't drill the barrel that big anyway....

Bob

Actually, inside diameter is of little concern to me- the 1/4" outside dia. is what I was after. Price was right, (free cast aways at work) and the original application is potable chilled water that requires inside fittings. If it was a Crosman, I wouldn't have bothered at all~ but anything beats the factory mush that the 78 series ships with...

I'm probably compressing them down quite close to your .165 in my 78's.

Regards,

Doc Sharptail

[sholo]

I'm not really a fan of poly tubing~ especially on a gun that is going to see a lot of dis/re-assembly that good tuning seems to require. I still like the metal t.p. of the xx systems, and stay with it as much as possible.

I'm not either, but it's pretty hard to get a 3/16" ID port using a 22xx metal sleeve...

Actually, inside diameter is of little concern to me- the 1/4" outside dia. is what I was after.

I'm the complete opposite - after seeing how even tiny changes in TP diameter affects fps/fpe numbers, ID is what's important to me. Being a .25 cal, I want the valve to "breathe" as well as it can. Just wasn't sure about strength or sealing ability using 1/4" vs 5/16" OD material.

Kind of redundant now anyways though as I picked up some 5/16" OD x 3/16" ID poly tube the other day. Figured if I was worried enough to ask the question in the first place, plus Bob pointing out that although 1/4" CAN seal properly with the thin wall (albeit a bit finicky), I decided to just go ahead and use 5/16" OD instead...