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PVC piston valve in progress!

Post questions and info about pneumatic (compressed gas) powered cannons here. This includes discussion about valves, pipe types, compressors, alternate gas setups, and anything else relevant.
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PVC piston valve in progress!

Unread postAuthor: drex » Thu Mar 17, 2011 11:29 pm

Its been a while, but I decided its a good time to get back into this hobby, so today I started machining a piston valve out of PVC and the piston out of nylatron. the bore is 3.5" and the ports are 2" ntp. I am making a removable back out of 1/2" polycarbonate, and I am going to pilot it with a one inch sprinkler valve.
I'm very excited!
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Unread postAuthor: mark.f » Thu Mar 17, 2011 11:48 pm

So... uh...

Any more details? Other than the fact you're machining the whole thing out of a gigantic chunk of PVC type I stock? :wink:
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Unread postAuthor: drex » Thu Mar 17, 2011 11:58 pm

I will upload the prints tomorrow they are on my work computer, its got a 6" od, 3.5"id, and is 6" long.
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Unread postAuthor: Technician1002 » Fri Mar 18, 2011 12:16 am

2 inch porting valve. Nice size. I think you will like it. Be sure to use a good bumper as that piston is a good size hammer with lots of momentum.
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Unread postAuthor: jackssmirkingrevenge » Fri Mar 18, 2011 2:39 am

mark.f wrote:you're machining the whole thing out of a gigantic chunk of PVC type I stock? :wink:


It does seem like it's going to be excessively heavy, will you be hollowing it out somehow, or forming it into a cup shape?
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Unread postAuthor: Gaderelguitarist » Fri Mar 18, 2011 10:24 am

will you be hollowing it out somehow


He did say the valve body was going to be pvc. So yes, I would hope he would be hollowing it out :D
Unless Jack is being sarcastic of course.....

You should be excited. This thing is going to be very nice. It will also look very VERY slick since it is being machined, as opposed to being maed from plumbing fittings.
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Unread postAuthor: Gun Freak » Fri Mar 18, 2011 11:15 am

I think he was asking about hollowing out the piston...
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Unread postAuthor: mark.f » Fri Mar 18, 2011 11:17 am

Image names clue us in a lot. The component up top was machined from the stock in the bottom picture, most likely, I was just wanting a few more specifications.
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Unread postAuthor: Gaderelguitarist » Fri Mar 18, 2011 11:19 am

Thats a probable probability. I saw "PVC" and assumed valve body, since in the original post, the author stated his piston would be machined from nylatron (the plastic cousin of Megatron).

Edit:

The component up top was machined from the stock in the bottom picture, most likely


And now I am less ignorant of things. :oops:
I should have made the connection........
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Unread postAuthor: drex » Fri Mar 18, 2011 2:41 pm

It is pretty stout, but how heavy it is is not really an issue to me.

Do you realy think I need a bumper? I will be using half inch polycarbonate for the back, I might even go up to, 3/4" to 1".
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Unread postAuthor: Gun Freak » Fri Mar 18, 2011 3:00 pm

YESSSSS always use a bumper. Half a tennis ball with a hole in the middle will be good.
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Unread postAuthor: Gaderelguitarist » Fri Mar 18, 2011 5:02 pm

Without a bumper, your piston will abuse the hell out of your valve housing. It will also be a lot more noisy with the loud crack of the piston flying back into another hard surface.
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Unread postAuthor: drex » Fri Mar 18, 2011 6:37 pm

okay, bumper it is then, I mad a bunch more progress today, thread milling pipe threads are a pain.
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Unread postAuthor: Technician1002 » Fri Mar 18, 2011 7:16 pm

The simple physics of the piston is Force = Mass X Acceleration. If you apply 500 LBS of force on the piston so it snaps open (figure pressure times area on the piston) It will accelerate over time to a high velocity. To decelerate it in say 1/8th inch, the force will be MUCH higher than the wimpy 500 PSI that pushed it open for a couple of inches.

How many tons is your piston capable of before it deforms against the pilot port? It may decide to slow down less than you intend as it slows over a longer distance as it comes out the back.

Plan on a safe stopping distance. Slowing to a stop sign from freeway speeds is low force over long distance or high force in a short distance, such as using the truck parked at the stop sign for brakes. Then the force is high and distance is short.
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Unread postAuthor: drex » Sun Mar 20, 2011 3:19 pm

I'm thinking of machining a bumper out of polyurethane, do you guys think that would be good or should I just stick with half a tennis ball?
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