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P.M. on 2" P. Valve launcher

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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P.M. on 2" P. Valve launcher

Unread postAuthor: motorfixer1 » Sat Sep 25, 2010 4:30 pm

I finally got around to posting some pics of my pneumatic launcher. I have around 100 shots through it so I thought it would be a good idea to check things over inside and take some photos! Specs include as follows:
3" chamber 30" long
1.5" barrel 48" long w/ muzzle knife
Cam-loc attachment
2" piston valve housed inside 3" tee and 3" coupling
"off the shelf" piston
Fully serviceable valve assy
Piston travels inside triple layer PVC
1" sprinkler pilot
All fittings Sch40 p.r.
Only tested at close range so far and the results are impressive to say the least. This thing needs a G.B. barrel stat.

I decided to build a launcher with as little machining as possible to prototype a piston valve that could be mass produced easily for a friend who wanted to try to sell a few of them. Needless to say, that did not work out and now I have a new launcher and an entire extra valve assy minus chamber, pilot valve and barrel for a spare also. The only lathe requiring steps were for the o-ring grooves on the rear of the piston and to make the service port plug and the o-ring grooves on its outer diameter.
The pilot chamber service port plug is four reducer bushings machined to solvent weld flush with each other and then faced off on both sides to clean up.

The major parts of the valve body consist of a 3" tee, 3" coupler solvent welded together with a stub of pipe and then the socket of the tee and the entire coupler are sleeved with 4" PVC that is solvent welded around the outside. The 1/4-20 retaning bolts for the service port/piston stop pass through three layers of PVC as a result.The rear of the barrel (piston face seal seat) has a 2" coupler with four 1" port holes drilled in the sides solvent welded about 1/4 of the way on to support and guide the piston during travel.

The piston is two reducer bushings on the rear 2.5" SPG down to 1.5" SLP and a 1.5" cap on the front with a machinery pad for the sealing rubber.

This launcher required no maintenance after 100+ shots with the exception of a little grease on the piston o-rings and some teflon paste on the service plug. All the internal parts look the same as the day it was new!

Unfortunatley I have no photos of the valve during construction. Any questions or comments would be welcomed as this is the first piston valve I have constructed. Start at the bottom of the photos and work your way up.
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Attachments
Combustion Potato launcher pics 021.jpg
On service stand with pilot removed.
Combustion Potato launcher pics 020.jpg
Combustion Potato launcher pics 022.jpg
Pilot valve, Piston assy and hardware.
Combustion Potato launcher pics 023.jpg
Close up of the piston, chamber fill hole is at the top of pic.
Combustion Potato launcher pics 024.jpg
Piston Seat
Combustion Potato launcher pics 025.jpg
Pilot chamber with piston installed.
Combustion Potato launcher pics 026.jpg
Pilot reinstalled
Combustion Potato launcher pics 027.jpg
Combustion Potato launcher pics 028.jpg
Reassembled and ready to go

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Unread postAuthor: jakethebeast » Sat Sep 25, 2010 4:49 pm

looks good, what kind of range are you getting?
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Re: P.M. on 2" P. Valve launcher

Unread postAuthor: Crna Legija » Sat Sep 25, 2010 6:55 pm

motorfixer1 wrote: Only tested at close range so far and the results are impressive to say the least. This thing needs a G.B. barrel stat.


read the post
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Unread postAuthor: Technician1002 » Sat Sep 25, 2010 7:32 pm

What do you have for a bumper for the piston. I have had several PVC parts fail over time and use. That style of piston valve is noted for breaking the housing. It works fine for a while and then breaks open.

I started a thread on the subject.
http://www.spudfiles.com/forums/pvc-is-fragile-t21334.html
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Unread postAuthor: motorfixer1 » Sat Sep 25, 2010 7:43 pm

I have a 1/4" rubber disc that is visible in the photo of the pilot valve assy for the bumper. It is siliconed to the service port and shows no signs of wear after 100+ shots at around 120psi. I dont even see any wallowing out of the bolt holes that retain the service plug/piston stop. There is also three layers of pipe that would have to break to see the same failure that your launcher did. I understand that PVC has a "life span" when being misused like this!! :)
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Unread postAuthor: dewey-1 » Sat Sep 25, 2010 8:10 pm

One question though?
Why do all the pictures say Combustion Potato launcher?

Looks good otherwise!
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Unread postAuthor: motorfixer1 » Sat Sep 25, 2010 9:15 pm

I never noticed that the photos were imported into the same folder that the combustion launcher is in. I guess I'm not that observent when loading photos on to the computer!! WOW, I previewed this post three times and still didn't notice that :shock:
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Unread postAuthor: Technician1002 » Sun Sep 26, 2010 12:20 am

motorfixer1 wrote:I have a 1/4" rubber disc that is visible in the photo of the pilot valve assy for the bumper. It is siliconed to the service port and shows no signs of wear after 100+ shots at around 120psi. I dont even see any wallowing out of the bolt holes that retain the service plug/piston stop. There is also three layers of pipe that would have to break to see the same failure that your launcher did. I understand that PVC has a "life span" when being misused like this!! :)


Force = Mass X Acceleration. This is true for stopping as well as starting. This piston has an acceleration distance of over a 1/2 inch and a stopping distance of less than 1/8th inch. Force in stopping is going to be very high. Rubber does not compress very well. It distorts. A flat piston hitting a flat sheet will compress it very little. Handle it like the pilot area is going to break off at any time.

A bumper needs to provide a safe deceleration zone to keep the force within reason.
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Unread postAuthor: BeaverRat » Sun Sep 26, 2010 12:45 am

I fact, rubber is the most incompressible material found on earth with a poisson's ratio of .49 (.50 is completely incompressible), instead, it deforms. If you are going to have a rubber bumper, make sure it has room to change shape. For my piston cannon, I used a rubber sheet, but rolled it into a tube as the bumper, so that it can collapse on itself to absorb the shock.
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Unread postAuthor: motorfixer1 » Sun Sep 26, 2010 7:28 am

What if I used a length of hose and bent it like a doughnut and used this instead of the sheet of rubber?
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Unread postAuthor: Technician1002 » Sun Sep 26, 2010 10:55 am

Rubber hose is often used as a bumper. I have not tried it but I hear it performs well.
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Unread postAuthor: Gun Freak » Sun Sep 26, 2010 2:32 pm

Interesting build there! It looks good, I think you should paint it. However... I have one comment... You have a HUGE pilot volume. You could have stuck the sprinkler right into the back of the valve, but you added all those 1" fittings! I think JSR might commit suicide lol. But anyway the sprinkler can handle it so it isn't that bad. Nice job 8)
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