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I was in Home Depot yesterday looking at copper fittings.

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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I was in Home Depot yesterday looking at copper fittings.

Unread postAuthor: boyntonstu » Wed Jul 08, 2009 6:51 am

Copper T's come in different size combination in addition to a uniform size such as a 1 x 1 x 1.

For example: 1 x 1 x .75; and 1 x .75 x 1

The last dimension is the opening at the bottom of the T.

If you look inside a cooper T like the 1 x .75 x 1 you will see a smooth taper where it reduces from 1" to 3/4".

A possible fitting for a tapered piston seal?

Has anyone used a solder copper fitting instead of a brass threaded fitting as the body of a piston valve?

BoyntonStu
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Unread postAuthor: inonickname » Wed Jul 08, 2009 7:00 am

Have a look at Rag's heal. That's exactly what you're talking about.
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Unread postAuthor: MRR » Wed Jul 08, 2009 10:10 am

There are quite a lot of copper guns in the pneumatic showcase.
You just have to look around.

In my opinion there should always be a threaded part in the piston housing to make the piston servicable.
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Unread postAuthor: boyntonstu » Wed Jul 08, 2009 10:44 am

MRR wrote:There are quite a lot of copper guns in the pneumatic showcase.
You just have to look around.

In my opinion there should always be a threaded part in the piston housing to make the piston servicable.


I agree.

A copper to threaded adapter would give access.

I was also thinking of using the copper fitting outlet surface (polished) as part of the breech seal to the barrel.

The barrel would be fitted with a rubber washer or an O ring.


The bolt action would bring the barrel tight up against it.


BTW This is a link to a very sensitive piston sealer that triggers at 10 psi.

http://www.youtube.com/watch?v=hBaNXMJHIV8


BoyntonStu


Me having fun on the TV news.

http://www.youtube.com/watch?v=0yBLJg0efmk
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Unread postAuthor: THUNDERLORD » Wed Jul 08, 2009 11:06 am

Awesome you made the news Stu!!!
what exactly was that thing??? :P
Next time you make the news could throw a personal web-site link in there.
I watched that clip first...Then the 10 psi piston valve/copper gun fire.
Hope you're planning on building one similar maybe???
(Hope you didn't show the reporters any spudguns)... :lol: 8)
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Unread postAuthor: frankrede » Wed Jul 08, 2009 11:32 am

boyntonstu wrote:
MRR wrote:There are quite a lot of copper guns in the pneumatic showcase.
You just have to look around.

In my opinion there should always be a threaded part in the piston housing to make the piston servicable.


I agree.

A copper to threaded adapter would give access.

I was also thinking of using the copper fitting outlet surface (polished) as part of the breech seal to the barrel.

The barrel would be fitted with a rubber washer or an O ring.


The bolt action would bring the barrel tight up against it.


BTW This is a link to a very sensitive piston sealer that triggers at 10 psi.

http://www.youtube.com/watch?v=hBaNXMJHIV8


BoyntonStu


Me having fun on the TV news.

http://www.youtube.com/watch?v=0yBLJg0efmk

I saw your 100$ elavator, pretty inventive if I say so.
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Re: I was in Home Depot yesterday looking at copper fittings

Unread postAuthor: Ragnarok » Wed Jul 08, 2009 1:29 pm

boyntonstu wrote:Has anyone used a solder copper fitting instead of a brass threaded fitting as the body of a piston valve?

You tell me. (Hint: The ball valve is just a safety for the main valve)

In other words, yes. It was a deliberate attempt to save on length (and dead space) over using a separate reducer.
It was not however anything to do with using a tapered piston seal. HEAL's piston valve had some special features of its own though.
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Re: I was in Home Depot yesterday looking at copper fittings

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Unread postAuthor: mark.f » Wed Jul 08, 2009 1:51 pm

Image
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Unread postAuthor: boyntonstu » Wed Jul 08, 2009 2:39 pm

mark.f wrote:Image


Thanks for the beautiful photo!

I see what appears to be a 1" T and what looks like a 1" copper to 1" NPT female adapter.

(Very neat soldering, you hardly baked the label)

If I had x-Ray vision would I see 1" copper inside the T beyond where it normally stops?

The piston: 2 piston/cylinder seals on the left or are they stabilizing washers?

Leather washers to seal?

What lubricant?

Please explain what seals and what causes the release in pilot pressure to allow the seal to unseal?

Thanks in advance,

BoyntonStu
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Unread postAuthor: Ragnarok » Wed Jul 08, 2009 3:21 pm

boyntonstu wrote:If I had x-Ray vision would I see 1" copper inside the T beyond where it normally stops?

No, you'd be able to see what was behind your computer monitor! :D
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Unread postAuthor: mark.f » Wed Jul 08, 2009 4:19 pm

Ha ha.

It's just a copper tee and female adapter, with a normal length of 1" copper pipe attached in-between which the piston slides in.

I actually redid this part, and then ruined it again by soldering on a union without attaching the threaded nut. :oops: But the other end of the tee has a modified 1" x 3/4" bushing (cut down in length so 3/4" pipe will slide through it), and a length of copper pipe with one end cut square and polished to form the sealing face. The piston also has been modified to include only one layer of 1/8" rubber for the seals (shorter, overall).

I've also made a copper piston valve before, and upgraded it, even.

*shuffle* *bang* *clatter*

http://www.spudfiles.com/forums/copper-piston-gun-t4289.html
http://www.spudfiles.com/forums/revised-copper-gun-t8378.html

EDIT: white lithium grease is my preferred lubricant of choice (for cannons, of course. :D )

EDIT II: elaboration on the piston seals on the left. They are 1/8" nitrile gasketing. I sandwiched them between the 1" washers, trimmed them with a razor blade, and then chucked the piston in a drill, spun it at a low RPM, and sanded the rubber as smooth as possible. Then, tightening the nuts will expand the rubber to seal in the piston bore.
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Unread postAuthor: boyntonstu » Wed Jul 08, 2009 6:33 pm

mark.f wrote:Ha ha.

It's just a copper tee and female adapter, with a normal length of 1" copper pipe attached in-between which the piston slides in.

I actually redid this part, and then ruined it again by soldering on a union without attaching the threaded nut. :oops: But the other end of the tee has a modified 1" x 3/4" bushing (cut down in length so 3/4" pipe will slide through it), and a length of copper pipe with one end cut square and polished to form the sealing face. The piston also has been modified to include only one layer of 1/8" rubber for the seals (shorter, overall).

I've also made a copper piston valve before, and upgraded it, even.

*shuffle* *bang* *clatter*

http://www.spudfiles.com/forums/copper-piston-gun-t4289.html
http://www.spudfiles.com/forums/revised-copper-gun-t8378.html

EDIT: white lithium grease is my preferred lubricant of choice (for cannons, of course. :D )

EDIT II: elaboration on the piston seals on the left. They are 1/8" nitrile gasketing. I sandwiched them between the 1" washers, trimmed them with a razor blade, and then chucked the piston in a drill, spun it at a low RPM, and sanded the rubber as smooth as possible. Then, tightening the nuts will expand the rubber to seal in the piston bore.


Thanks for the information.

I have read your posts an I have seen your photos and I salute you!

Did the QEV pilot improve the power?

Have you thought of using "Just for Copper" glue instead of soldering?

I want to use 3/4" M throughout.

Have you made a breech loader?

My goal is to have a single pump 300-400 psi rifle using a homemade stirrup pump.

I also have some other crazy ideas like using a ratchet bar clamp to press in a 0.5 sq in piston with a 200 lb force for 400 psi.

I want the smallest chamber that will do the job and that will fill easy.


BTW This valve is so sensitive that by just pressing the Schrader sets it off. His piston is made out of Bondo and it is very low mass (no bumper).


http://www.youtube.com/watch?v=VG3jISenqas&eurl

Much thanks,

BoyntonStu
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Unread postAuthor: MRR » Thu Jul 09, 2009 12:08 pm

I watched the video....

A good sealing piston with a tiny equalization or even a build in check valve will actuate with the smallest pilot valve at low pressure. On the other hand, if you don't provide negative pressure fast enough, the piston will compress the left over air in the pilot volume and the performance will suffer.

Keep the pilot volume as small as possible and small pilot valves should be no problem.

If you are searching pistons with low mass, I can recommend JSR's tutorial in casting with epoxy. He is an expert in pneumatic guerrilla tactics.
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Unread postAuthor: Technician1002 » Thu Jul 09, 2009 12:43 pm

MRR wrote:I watched the video....

On the other hand, if you don't provide negative pressure fast enough, the piston will compress the left over air in the pilot volume and the performance will suffer.

Keep the pilot volume as small as possible and small pilot valves should be no problem.



This is a common misconception. On a good close ratio barrel sealing piston valve, a little pilot volume is desirable so the pressure doesn't rise too high in the pilot when fired. A good design has about 3/4 to 85% of the face area of the piston exposed to the barrel and not the chamber. This leaves 15-25% of the piston face exposed to the pressure in the chamber. This means the pilot area pressure must drop to 15-25% of the chamber pressure to balance the closing force by the pilot with the opening force by the chamber. When the forces are equal is when the force sealing it on the barrel is gone.

When it pops open, (close ratio pistons do go bang even with a slow pilot), the chamber pressure opens the piston and the piston area exposed to chamber pressure now jumps from 15-25% to 100% A pilot that is too small can suddenly rise in pressure from compression and limit travel and speed. A larger pilot, for example about twice the volume taken by the piston movement will limit the pilot pressure rise to just double by the halfing the volume by piston travel. This rise in pilot pressure by halfing the volume is then double the absolute pressure.

Examples are for a 15% area piston.. 100 PSI chamber, fires at pilot pressure of 15 PSI.. or two Atm. From piston movement to 1/2 volume that's 4 Atm, or 3 bar. With the face exposed 100% to chamber pressure, this piston will snap open and remain open until the chamber is below 3 Bar pressure. This is how a QEV works. This is what makes them snap open.

Using too small a pilot volume on a close ratio valve including a QEV can hurt performance. Do the math people. Model it and examine how it works. Most QEV's will have enough pilot area when you add a short length of pipe and a trigger valve. Their pilot area is small inside the valve.

Attached again is the sound of the Mouse Musket firing. Compare it to the sound of his in the video. It has a sssssBoom. A fast pilot or very small pilot are not needed to make these work at peak performance.

My latest 3 cannons have taken this ratio to an extreme. The piston seat to diameter ratio is 1:1. To model it, there is no force on the piston when the pilot pressure is 1 atm (0 PSI) 0 bar. It requires a gentle mechanical pull to unseat it. When the valve is unseated, the piston again compresses the pilot area to about 1/2 the original volume or 2 atm or 15 PSI. This is in contrast to the 100 PSI chamber now exposed on the face. 100 PSI vs 15.. It opens all the way and remains there. As the chamber pressure drops, so does the pilot as it has a large vent. This style has the boom without the hiss.

EDIT.. Adding some info on the waveform below. The sound was recorded on the computer with Audacity. The trigger is a 1/4 inch ball valve opened slowely. this is why the hiss starts small and builds to a peak. After the peak is reached, the pilot pressure dropping caused the hiss to drop off again. This is clearly seen. When the pressure dropped off the main piston lifted and the opening is very quick and loud. The sound recording equipment clipped the signal so the boom has the flat clipped signal. Following the main discharge many room echoes and barrel resonance lingers on.
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Attachments
Musket Discharge.png
Hisssssss Boom of a proper piston valve opening.
Musket Expanded.png
Expanded view of the hiss boom event. Valve opening time is delayed, but very fast when it happens.
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Unread postAuthor: MRR » Thu Jul 09, 2009 2:18 pm

Keeping the pilot volume as small as possible is an practical issue for me.

I experienced that it is hard to make a really well fitting piston without professional equipment. If the piston doesn't fit properly or the equalization is to big a small pilot volume helps to reach the actuation point.

Your QDV uses a mechanical "trigger" and industrial QEV's are fabricated on a very high scale.

Another point is, if you try to go semi / auto, you fill from the chamber. A small pilot volume will make the piston seal faster because of the faster equalization. I think that's the main reason why I prefer small pilot volumes.
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