SpudFiles

Well, on my quest to the .40 calibre bolt action dartgun, i have an interesting design constraint......

I want my gun to be as compact as possible. I have some REALLY NICE maple for the stock and i want to make the entire gun fit inside of it, and look like a Bullpup PCP air rifle......

Attached is a quicly sketched picture of what i want. Basically, i want to fill through one end, pilot through the other end, and have the flow go out the top. And most importantly, i DO NOT want to build a chamber sealer. this will be used at pressures ranging from 150 to 400 PSI.........

and also, if possible, the other design constraint is for it all to be INSIDE of a 3/4 inch Galvanized steel pipe............... nothing sticking out around the OD of the pipe besides the air outlet........

I have my ideas but id like to see what you guys can come up with. my idea is a little hard to do........

i also forgot to mention i plan on using epoxy..................... lots of epoxy.

Umm, the only example I'm aware of is in diaphragm solenoid valves where air from the fill side leaks into the pilot area to seal against a seat.

Making life hard for yourself eh?

Out of interest, where have you been reading that chamber sealers won't work at that pressure

Its just i dont want to have to deal with the annoyance of making sliding air seals with o-rings. to finniky.

my goal was to use a cylinder of Hard Rubber as the piston, negating the need for a "sealing face" that could come off without warning, ect.

The final result will be, damn sexy, to put it simply, so just bear with me... lol.

Sound like you had an attack of the myths

O-rings are not required, neither is a sliding seal, in fact it can look EXACTLY like a barrel sealing piston with just the barrel and chamber swapped over.



Oh and an equalisation hole.

Unfortunately as you've got a design requirement of chamber side filling you might need a spring to keep the piston held shut until the pressures are equalised.

Friction might be enough but I'd not bet anything on it holding if you dumped a compressors air tank in.

Hotwired wrote:Sound like you had an attack of the myths

O-rings are not required, neither is a sliding seal, in fact it can look EXACTLY like a barrel sealing piston with just the barrel and chamber swapped over.



Oh and an equalisation hole.

Unfortunately as you've got a design requirement of chamber side filling you might need a spring to keep the piston held shut until the pressures are equalised.

Friction might be enough but I'd not bet anything on it holding if you dumped a compressors air tank in.

If you havent got a sliding seal, wouldt it leak pressure from the pilot to the barrel?

Blast, and the posts been quoted too

A flared piston end of another design derailed me on sealing ^_^

Nevertheless

It's still mostly good. The option is there to be creative with the rubber piston or cut a groove in to put an o-ring

Speaking of wich, what are some good ways to make O-rings 100% "sealy"..... i really dont trust my grove cutting skills..... and remember its going to be taking HUGE amounts of pressure............

and remember its going to be taking HUGE amounts of pressure............

I thought you said your maximum operating pressure was 400 psi? Which is it? Because 400 psi doesn't really require anything beyond the norm, except maybe a bit more consideration of piston materials and design.

Go for the chamber sealer, cast the o-ring into an epoxy piston.

Use a greased 3/32" cross section o-ring for the casting.

Remove the o-ring after the epoxy has cured, and file the groove to the proper size for an 1/8" cross section o-ring.

o-ring chart here;

http://142.179.166.227/hitechseals/pdf/ORingChart.pdf

Thanks for all your help guys, but im still interested in seeing how i could keep this a barrel-sealing gun.................

im going to try my hand at 100% sealing of things, but dont expect anything. im still a little hesitant on the 0-ring part, im not so great with o-rings..................

The problem is that you're wanting a barrel sealer in a chamber sealers configuration.

Short of having a 90* bend come in from the exhaust port for a piston to seal against it's not really possible to HAVE a barrel seal as it needs the exhaust to be opposite the pilot.

what you could do is build it like a coaxial, but then bend the barrel out the top of the camber. This is nice because of compact-ness, but a requires creative construction.

Bah youve all convinced me to build this all in 3/4 inch copper pipe..... i have a GREAT idea to make it 100% take-downable......... if i can get O-ring seals perfect.......