Air Gun Home :: View topic - Poly Seal Blowing out at high pressure so switched to nylon.

69Hotrod69 · Veteran Member

I was doing some testing on my Disco with JRA breech and ran into an interesting problem with my 2400PSI regulated pressure. I had a poly tube with an o ring on each end initilaly using 1600 PSI with no issues. When I switched to heavy hammer spring(.047 wire 1.625" long) and 2400PSI it blew both orings out the barrel. Shocked

I then went to just the poly tube and it blew a hole in it the size of the port. The HPA grabbed the edge of the tubing on the angle side of the tranfer port and ripped a hole in it. Rolling Eyes

I switched to a nylon tubing I use on air ride suspensions that I build for custom cars and trucks and it held up fine, but the high pressure makes the valve(modified B&A) act very erratic and I believe its in lock most of the time. It did send a shot acroos the chrony with 14.3 pellet at 1464 though. Shocked

Was not repeatable though, closest to it was 1356. I wasnt interested in using this pressure for the rifle just playing around with pressure and springs and thought the tubing thing might be of interest. The nylon seems to seal as well but it must be cut and sanded for a perfect fit(it's quite a bit harder). I put 150# of vacuum on the barrrel for an hour and it held. It is working well in the rifle now with 2000PSI. Smile

I would not recomend the 2400PSI on the disco tube it was just for an experiment. IMO its too much pressure for the tube.

AirGunEric · Site Admin

This is a JRA riser breech or something?

I have never liked the idea of a poly tube seal- Crosman uses a steel sleeve with one o-ring seal at the end to compress the steel against for a decent seal. I am assuming this is a riser breech setup of some sort, and thus the factory steel sleeve setup cannot be used?

Mark5043 · Silver Status Member

Sounds like you have a workable solution to that transfer port issue.A-little ingenuity goes along way.!1464 with a 14.3?.....That's 68 FPE.... Shocked

If your hitting those numbers you have a MONSTER of a Disco on your hands.Your up there in Condor territory....and then a-little. I would have doubts as to your valve being locked up most of the time as you say. You'd be dumping a ton of air to get those numbers...

Out of obvious curiosity,based on your numbers...what mods did you do to that B&A valve?With that valve in stock form,and the hammer spring your using,you'd have some good numbers,but 68 FPE?????That's the far side of the moon.What's your shot count like?I wouldn't think you'd have much of one,before the next fill.... Laughing

At 2400 PSI your well within the safe limits of the Disco tube....no worries there.... Mr. Green

69Hotrod69 · Veteran Member

Yes its a 10 shot riser breech, uses the Marauder mag. I like the crosman steel seat with rubber seal as well, but no it can't be used. Crying or Very sad

When I get my lathe up an running I will make a sleeve similar to the Marauder. Cool

I just thought for people having problems with poly tubes where they must be used the nylon tube may be a better option for higher pressures. Smile

I believe some people have made Delrin tubes as well but that requires a lathe which is not an option at this time.

I have had great success with the poly seal and a small piece of tubing(.105id) on my FT rifle. This rifle needs the .172 diameter so theirs no room for a sleeve. It currently produces a max of 52FPE on 2000PSI regulator. The nylon has around 100 shots through it and still holds a vaccum. Wink

I have also put vacuum on Crosman seals some hold some don't, a dab of locktite on the barrel to steal sleeve and it solves that problem.

rsterne · Moderator

I use a taller version of the Crosman steel sleeve in my riser breech.... Carefully made on a lathe it works just fine.... although I can't imagine it would hold a vacuum with the metal to metal joint at the barrel.... On the other hand, the pressure pulse is so short during the shot I don't think the losses are very great, either.... and there is no problem with it blowing out or collapsing....

If you're getting 68 FPE you're not getting valve lock.... Considering that is with a 14.3 gr. pellet, I'm guessing that with a 28 gr. EunJin you would be up at least 80 FPE.... Shocked

My Disco maxed out at 52+ FPE in .22 cal (909 fps with 28 gr. EunJins).... and about 58 FPE in .25 cal (919 fps with 31 gr. Baracudas).... In both cases I was filling to 2400 psi and the peak velocity was at 2000, with 9-10 good shots in both calibers (unregulated, using the Disco tube).... I never went more than 0.040" wire on the hammer spring, however, and that was the limiting factor....

Your gun must be a BEAR to cock.... Mr. Green

Bob

Mark5043 · Silver Status Member

kanyon · Silver Status Member

i just make a steel port then screw it in to the valve
with a 0-ring

69Hotrod69 · Veteran Member

Why I thought it was in valve lock at higher pressure was because it shot 3 shots around 760FPS, then 1464, 1356, 1240, then it blew the tube out. I really don't like the disco tube holding 2400PSI but maybe in th future with a better tube I'll revisit the 2400PSI Regualtor. By the way even with the Marauder shroud those three shots were very loud.

69Hotrod69 · Veteran Member

Most the mods to the B&A valve are to the Disco Stem I use it is .0625 shorter and relieved to .110, the seal is just a little larger than the seat ~.025, and all excess material removed. I use a Muzzle Macks extender to get rid of the gauge port. The extender is slightly modified threads cut down to .3 softer and longer spring is installed with the seat in the extender drilled back~.125 it is also drilled just enough to hold spring but allow air in then tappered to front.

The hammer has a notch cut out where the sear used to drag, the spring is .047 wire cut down to 1.625 length then stretched to 2.0 and heat treated.

If the tube really can handle the 2400PSI with out issue, I may play with it some more but the fact of the matter is it will probably be a decreasing curve with only a few good shots, and surely not ten.

I have another Disco tube maybe I'll set ti up with single shot breech to play with the 2400PSI set up. I can easilly make more springs.

69Hotrod69 · Veteran Member

Bob,

This is pretty much a copy of your 22xx PCP on 2000PSI except for the B&A modified valve and the breach of course. It actually performs almost identical on 2000PSI. It took a little work to the breech to get it to perform this well.

Again thanks for all your posts!

rsterne · Moderator

69Hotrod69 · Veteran Member

Bob,

If I put the rifle back in this configuration I'll give it a try further back I was only 18" inches from the chrony. I thought in general this was far enough back.

The vacuum was a typo I meant 15" HG. Embarassed

This post was meant to be about a good seal, but now I will do my best to reproduce the results I got. Fluke or not!

At coil bind it does feel like the cocking hammer may fail.

69Hotrod69 · Veteran Member

Bob,

If I fill just the tube with 2400PSI instead of the regulator I should get close to the same results if I max out the spring right? At least for the first few shots?

rsterne · Moderator

For 1 or 2 shots you should....

Bob

69Hotrod69 · Veteran Member

I'll try just filling the tube, much easier than changing the regulator set point again.