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1 1/2 inch piston valve

Built a pneumatic cannon? Then post it here! This section is for completed, finished cannons that you have built. Please include pictures and information.
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1 1/2 inch piston valve

Unread postAuthor: LikimysCrotchus5 » Sat Oct 20, 2007 10:52 pm

Well i am about to finish my first piston valve. This will be my fist working one, i hope. The reason why it is small is because home depot (which i now hate) has barely any presure rated parts so i had to make a gun with what i could get.

Specs:
Piston: Hot Glue, or Cast Ethylene Vinyl Acetate (as Spudblaster likes to call it :D)
Sealant Face: 2 Layers of tire inner tube
Bumper: Mouse Pad

Some Pics

Image

Piston

Image

Sealant Face

Image

Bumper

Image

Piston in Tee

Image

Piston in Tee with barrel

Well i just made the gun today and i put it together. I tried it ( after 15 minutes if drying),and i know i shouldnt do it but i did, and it didnt work and i got mad. So then i just sawed off the cap anf i looked inside and the piston is fine. I think the problem is that i am usuing a schracer valve and it didnt seal because there is not enough pressure pushing on the surface area of the piston and there is not enough flow and speed pushing against the bacl of the piston. Or it is the sealing face since its double layered. So i dont know which one is it? Or if its neither? Please someone tell me whats wrong. This is my second valve and both didnt work. Please help. :(
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Unread postAuthor: spudgunnerwryyyyy » Sat Oct 20, 2007 10:58 pm

Well, nice piston valve. You probably need at least 10 psi for it too seal and 20 for energetic actuation. Pm me if you have any problems as i was in your situation talking to Mr. Crowley 2 weeks ago so pm me if you have any problems. Most people bolt on their rubber, i did and it works great.

Is the piston sliding in 2" pipe or the tee, Mr. Crowley and I found sliding in 2" pipe is way better and more efficient.

Go to a hardware store and buy white lithium grease and smear it all over the sides of the piston.

need any more help pm me.
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Unread postAuthor: hi » Sat Oct 20, 2007 11:00 pm

it looks ok to me. if it didnt pop open after only 15 minute of drying, then you probably didnt use enough pressure. i know one of my valves doesnt work unless its at about 45psi or so.

seriously though, glue to together, put it in the garage, and forget about it until the next day. i know the urge to shoot it, but do it right the first time, trust me, it helps.

edit- if you dont have lithium grease (suggested in the post above) you can use PAM, yes pam, the cooking spray.
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Unread postAuthor: spudgunnerwryyyyy » Sat Oct 20, 2007 11:04 pm

Yes but pam is messy and not thick enough, it may work at first but after hundreds of shots maybe not so well.
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Unread postAuthor: LikimysCrotchus5 » Sat Oct 20, 2007 11:05 pm

How about vaseline? i used it in the tee and it seemed to work well
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Unread postAuthor: spudgunnerwryyyyy » Sat Oct 20, 2007 11:08 pm

Well it is a petroleum product(petroleum jelly) and petroleum products have been known to degrade pvc and rubbers. Silicone grease also works. But does the piston slide in 2" pipe or in the tee it self.

With the piston sliding in the tee i never got it to work, but in the more consistent surface of the pipe it works great.
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Unread postAuthor: MrCrowley » Sun Oct 21, 2007 1:10 am

If your sealing face isn't bolted on with a decent sized washer, your sealing face will blow off if you gun has any power at all, if it stays on your gun isn't powerful enough, either way you're screwed :P

Don't give in to the temptations, wait for the glue to dry at least 24hours in a pneumatic, especially a piston valve.

If your piston isn't tight enough fit in the tee, and it has no lube you will not seal the valve with a bike pump and schrader. If it is a good fit and has lube you should be able to seal it with a schrader valve and a bike pump if you can pump fast enough.

Have you accounted for the 'lip' in the tee that changes the I.D of the tee just before it reaches the opening port inside it? If you haven't you should get some pipe the same nominal diameter as the tee, by a plug reducing bushing which threads down to 1/2" or 1/4".

Cut of a inch or two of the pipe and stick it inside the tee but make sure the plug has enough room to fit inside so you can bolt it on from the outside of the tee. The get some scrap pipe thats the same as the one you just put in the tee, and recast your piston from hot glue in it. Bolt a sealing face on with a washer, make sure the washer won't leak air from behind, and find a better bumper then a mouse pad.

Then get either 1/2" or 1/4" brass or galv fittings for the plug, then setup your pilot setup with guage, fill valve and pilot valve, and thread it into the threaded plug on the back of your tee, then bolt your plug in and you should be set, if the plug leaks use some silicon to seal it up.

Oh and since you tested it after 15min you risk putting bubbles in the solvent welded joint, which makes the weld weaker and possibly leakable.

@hi

If you can't seal one of your piston valves until 45psi, you should make a new one, I can seal mine at 5psi and actuate it at 8psi no problem.
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Unread postAuthor: SpudBlaster15 » Sun Oct 21, 2007 11:39 am

Is it just me, or are 2 ridges present on the surface of your sealing face?

MrCrowley wrote:If your sealing face isn't bolted on with a decent sized washer, your sealing face will blow off if you gun has any power at all, if it stays on your gun isn't powerful enough, either way you're screwed :P


There is no need to bolt the sealing face on. My copper piston gun has it's sealing face attached using CA glue, and the face shows no signs of detaching, even after actuating the valve 5 times at 300psi.
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Unread postAuthor: LikimysCrotchus5 » Sun Oct 21, 2007 11:52 am

Well the reason why i didnt bolt on the barrel is because i saw the tutorial on how to make a piston valve by BC Pneumatics. And i know my design is different than that one shown in the video, but he did use hot glue to glue on the sealing face to the hot glue piston, so i did the same. So would hot glue be strong enough to hold that sealing face on the piston?
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Unread postAuthor: origin unknown » Sun Oct 21, 2007 1:11 pm

What happened when you fired it? Did it leak air before firing it? Did it exhaust most of the air when you fired it and the piston opened only to let a small portion of the air out? What are you piloting it with? What size chamber did you test it with?
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Unread postAuthor: MrCrowley » Sun Oct 21, 2007 5:02 pm

SpudBlaster15 wrote:Is it just me, or are 2 ridges present on the surface of your sealing face?

MrCrowley wrote:If your sealing face isn't bolted on with a decent sized washer, your sealing face will blow off if you gun has any power at all, if it stays on your gun isn't powerful enough, either way you're screwed :P


There is no need to bolt the sealing face on. My copper piston gun has it's sealing face attached using CA glue, and the face shows no signs of detaching, even after actuating the valve 5 times at 300psi.


How big is your seat? If the seat isn't big enough to have a washer on the sealing face then you wont need a bolt, but once you get up to seat diameters around 1 1/2" it will blow off.
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Unread postAuthor: SpudBlaster15 » Sun Oct 21, 2007 5:18 pm

Why would seat diameter matter? The velocity of airflow is what will tear the sealing face off, and this is mostly dependent upon initial chamber pressure, not the piston's seat diameter.
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Unread postAuthor: MrCrowley » Sun Oct 21, 2007 5:33 pm

Well i've made a piston for a small 1" co-ax, I glued the face on like you did. It didn't get ripped off at pressures around 120psi.

My bigger gun, with a seat of 1.5" the sealing face was ripped off even though it was glued and bolted (no washer), this is at 120psi, the increase air flow into the barrel is I guess what does it, because it was at the same pressure, the only difference was the chamber size and seat diameter, which has a lot more flow.
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