piston valve

[mouz]

iv'e been wanting to make a piston valve for a while, and i'm thinking i want to test the idea on a low pressure air pistol made of CPVC, i might even have it shoot BB's, but i don't think so. what does everyone think? is there any advice on building piston valves that i might not know?

[Forum Admin]

Making a piston valve is always a good idea, something different to play around with. I tend to move all over the valve spectrum when building airguns, each type of valve has its advantages at different times. Some advice for you:
1. Be sure the piston is serviceable, most pistons do not work the first time until you have practice making them.
2. Be sure you build the piston in such a way that the sealing face is held by a bolt, nut, and washer. Do not just use a screw, they do pop under pressure and use, causing an accidental discharge.
3. One of the most common sources of leaks is at the sealing face, often under the bolt. Use a bit of super glue on the threads and torque the sealing face down good to prevent leakage.

[mouz]

hmm, ok. i'm planning to have trigger and fill valve the same, a schrader valve. the gun will only take 100 psi.

[mouz]

this will happen next sometime soon, maybe within the next week.

[FighterAce]

Did I get you wrong or you meant that fill valve and trigger valve will be the same schrader? You're looking at some really bad performance if the valve even opens... equalization holes and schrader pilot valves dont do together very well if you dont balance them correctly.
You should rather go with a ball valve if this is your first piston valve and start from there. Gain experience and better understanding how they work and how to make them better.

[mouz]

a ball valve is $6. would it really be that much easier? because if it would increase performance/easiness i would spend that. oh wait i just remembered I HAVE A 1/2 INCH CPVC BALL VALVE........  why didn't i think of that earlier?!??!!?

[FighterAce]

The pilot valve with miniature flow (like the schrader) requires really really small pilot volume and a leak proof piston to perform at its best. By leak proof piston I mean that the air from the chamber cant get into the area behind the piston.

With a ball valve, it doesnt matter how much pilot volume there is because its got excellent flow..

btw. how are you going to service your piston if its gonna be housed in CPVC?

[mouz]

service it? i don't quite get the terminology.

[Forum Admin]

Piston valves dont always work the first time you build them, sometimes they will leak. You want to be able to pull the piston out and fix it, that's what he means by servicing. My first couple piston valves were non-serviceable, and they gave me fits. Sealing faces wear out as well and need replacing, so if you want to use your airgun longterm, you'll need to build in such a way that you can take the valve apart.

[mouz]

ok, i'll have one of the joints hot glued together. and i have done tests, hot glue can take 100 easy.

[FighterAce]

hot glue can take 100 easy.

Have you done tests at temperatures of 100 - 110 deg? My guess is that its gonna pop like popcorn 

[mouz]

yes it probably would, but it is not that hot here. it gets above 80 about once a year.

[boar]

it gets above 80 about once a year.

how are the gun laws up there i might want to move

 Boar

[Forum Admin]

I second that, the heat has been a killer this year. 

[mouz]

well i don't really know what the gun laws are like, but i do know your not allowed to have a double edged knife. or a switch blade.