piston question

[spudy buddy]

ok i looked around but i still need help. i get how pistons work but not what size to make them cause i don't know where they seal. do pistons seal at the yellow line or the purple line?[/img] sry i'm such a noob and don't quite get it so plz don't yell at me.

Edit: i'll try to fix the quality

[jackssmirkingrevenge]

the face of the piston seals against the edge of the barrel (purple line) while the o-rings seal off the chamber along the sides of the T (green lines to either side of the yellow line).

Ntw, paint does have a text feature, you don't have to scribble out the labels

[MrCrowley]

yeah what JSR said, though the seat (barrel/purple line) has to be a smaller diameter then the face of the piston.

This is so that there is air pressure pushing the piston back, and when the air pressure behind the piston is gone (i.e you empty the pilot volume with your pilot valve) the pressure pushes the piston back and opens the barrel up to air flow.

You don't need o-rings btw, they just increase performance.

[spudy buddy]

so do i make the piston so it can slide in the pipe to the pilot and a bit thiker on the other sid so it blocks the barrel or the size of the ledge(green)? and yes i totaly forgot paint had a text option sry

[MrCrowley]

Sorry what was that?

Try going over these two topics until you really know what you're doing. Then if you still have a problem, i'm all ears

How-To: Make a 2" piston:(diagrams on how they work and stuff)
http://www.spudfiles.com/forums/how-to- ... 10381.html

Piston valves explained visually:
http://www.spudfiles.com/forums/piston- ... t8157.html

I'm aware you may already have seen them, but you don't grasp the concept as much as I would like you to before building a piston, so just make sure you know what you're doing 100% first.

[SpudUke5]

let me c if i can dig up one of my old paint photos.



This is a very bad photo but bear with me. Ok for the size of the piston, in your diagram it should fit the diameter of the blue line. The sealing face has to be smaller than the barrel. You want to make the piston tight. You want to make the piston long enough so that it reaches the barrel and doesnt fall off the pipe that its fitted to.

[jackssmirkingrevenge]

I'm in a godawful patient mood for a Sunday morning, here:

edit: modified diagram slightly to address MrCrowley's concerns

[MrCrowley]

If you're lucky i'll spend a few hours making a new animation tomorrow, my old one is a bit worn out, but in the mean time JSR's excellent diagram will do.

[spudy buddy]

ok ty guys. i'm in no rush i haven't even tested my first gun. ya the diagrams are great but how much larger do i need the piston to be? a 1/2 tee won't work for a 1/2 barrel? and i know i have now where near enough knowledge to start a piston gun i was just gathering info. thx alot guys

[MrCrowley]

You could get it to work but it'd be a hassle and have poor performance. It'd be much easier to go 3/4" or even better 1".

[spudy buddy]

well in that case could i make one with the barrel inside the chamber out of 1 and 1/2 inch cause i have alot of both or would i need like a 2 inch pipe?

also what except an inter tube can i use for a sealing face?

[MrCrowley]

Yeah that'd work, 1.5" would be better, but it's up to you.

Neoprene rubber from your local hardware store, if they don't sell try neoprene/rubber plumbing gaskets, they're round disks found in the plumbing area usually.

They have a hole in the middle but as long as your seat(barrel) is bigger then this hole, it's fine.

[spudy buddy]

ok thank you i'll have to remember that when i go to the store. also for a co-axial at the end where the chamber stops but the barrel continues what do you use cause i see on some that there is just an end cap with a hole in it but how would u make it air tight? and what do u use on the other end for a servisable type piston? last question how do you make sure that the barrel stays centered(don't u have to put "spacers" on it or something although i have no idea what those could be)? ty

Edit: the above post i mean 1 inch and 1/2 inch not one1/2 like i worded it sry if it confused somebody.

[MrCrowley]

1) Just use a regular pressure rated bushing, may be tricky to push the pipe through though.

For the end cap, some people just use epoxy to help seal it.

2) You can use threaded adapters which increase pilot volume unless you have a long piston or fill the pilot volume with something. Or bolt a plug in, but you may have sealing difficulties unless you have o-rings on it.

3) Yeah you do, just go to the hardware store, up to your garage or look around your house and improvise.

Seriously things like that you just need to think of yourself as they're not store bought all the time. Just improvise, look around places for something that could be used.

Use your imagination.

[spudy buddy]

ok so i'm thinking of making a co-axial with 1 inch pipe for the chamber and 1/2 for the barrel. i'll make the piston atleast 1 inch long (probably more) out of hot glue.not sure what i'll use for a sealing face but i'll look around the house and store. a bushing on one end and something on the other that i can open. pilot valve will be one of these: schrader(not likely), blowgun(most likely), or pvc ball valve. everything sound ok or have i got something wrong?