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Does your T piston valve open completely and stay open?

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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Does your T piston valve open completely and stay open?

Unread postAuthor: boyntonstu » Sun Apr 18, 2010 10:59 am

My Trom-Boyn design allows me to fire the chamber without its slip in barrel to allow inspection of the piston after firing.

Ideally, the piston should slide backwards to expose the complete diameter opening to the chamber side of the T.

If you can stop bounce the final piston position will be wide open.

Today was the first time that I succeeded in opening and stopping the piston in the optimum position.

An added benefit is that when slammed open, the piston seals the pilot preventing further air loss.

What a BLAST difference a wide open valve makes!

It is like I have made a new gun.

It took a lot of trimming and shaping on the rear of the piston plus I had to design a completely different shock absorber and piston retainer.

I wish BTB would write an ode to the Trom-Boyn.

Since you can't blue copper, the song cannot be the Blues.

:roll:
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Last edited by boyntonstu on Sun Apr 18, 2010 11:30 am, edited 1 time in total.
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Unread postAuthor: Technician1002 » Sun Apr 18, 2010 11:11 am

Between no pilot pressure at all when triggered, a good bumper, and an orifice into the stopper behind the piston acting like a daspot, my 2 inch remains open until most of the chamber is vented, then it tends to close due to some pressure build up in the pilot area. 100 PSI shots sometimes trap up to 5 PSI in the 3 gallon chamber. I think most of the trapped pressure is from the valve returning closed after the chamber reaches zero, then the cooled by expansion air in the chamber warms up from the room temperature parts.

When fired, when there is pressure in the chamber the valve is held fully open for the duration of the shot on my cannons.
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Unread postAuthor: Hawkeye » Sun Apr 18, 2010 12:59 pm

I think it matters more if the projectile is gone rather than the valve remaining open. Optimum length of barrel is more important than valve open time.
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Unread postAuthor: boyntonstu » Sun Apr 18, 2010 1:08 pm

When you open a valve part way the full potential of power may not be achieved.

In my cannon, the piston length was too long for complete opening.

Little leaks do not make major blasts.
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Unread postAuthor: Labtecpower » Sun Apr 18, 2010 1:13 pm

My piston valve stays completely open after firing the cannon.
when I pressurise it with my bicycle pump, I hear a nice "thump" at the first stroke. My pilot volume is about 40 cubic cm.
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Unread postAuthor: Hawkeye » Sun Apr 18, 2010 4:23 pm

I think you're missing the point of efficiency. A loud blast produced mainly by air exiting after the projectile is gone does nothing for velocity.
Remember the rule for actual piston movement for optimal efficiency.
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Unread postAuthor: boyntonstu » Sun Apr 18, 2010 4:45 pm

Hawkeye wrote:I think you're missing the point of efficiency. A loud blast produced mainly by air exiting after the projectile is gone does nothing for velocity.
Remember the rule for actual piston movement for optimal efficiency.


The blast was just the chamber.

No barrel, no projectile.

I listened to the chamber blast firing many times but it was never as loud as today with the mods.
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Re: Does your T piston valve open completely and stay open?

Unread postAuthor: velocity3x » Sun Apr 18, 2010 5:12 pm

[quote="boyntonstu"]What a BLAST difference a wide open valve makes!
quote]

Amen to that! That's why I only build full flow, fully retracting valves. It's not a popular idea here as the D/2 or D/4 idea is the holy guideline.
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Unread postAuthor: Hawkeye » Sun Apr 18, 2010 8:30 pm

boyntonstu wrote:
Hawkeye wrote:I think you're missing the point of efficiency. A loud blast produced mainly by air exiting after the projectile is gone does nothing for velocity.
Remember the rule for actual piston movement for optimal efficiency.


The blast was just the chamber.

No barrel, no projectile.

I listened to the chamber blast firing many times but it was never as loud as today with the mods.


I know, I'm saying that only a fraction of that blast is actually acting on the projectile unless your barrel length is optimal.
Notice that Brian's repeater essentially works on the principle of just popping the piston open for the optimal amount of time. Still packs a hell of a wallop because it's using that burp of air more efficiently than your gun roaring like a twelve gauge after the projectile has struck the target..
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Unread postAuthor: boyntonstu » Sun Apr 18, 2010 8:45 pm

Hawkeye wrote:
boyntonstu wrote:
Hawkeye wrote:I think you're missing the point of efficiency. A loud blast produced mainly by air exiting after the projectile is gone does nothing for velocity.
Remember the rule for actual piston movement for optimal efficiency.


The blast was just the chamber.

No barrel, no projectile.

I listened to the chamber blast firing many times but it was never as loud as today with the mods.


I know, I'm saying that only a fraction of that blast is actually acting on the projectile unless your barrel length is optimal.
Notice that Brian's repeater essentially works on the principle of just popping the piston open for the optimal amount of time. Still packs a hell of a wallop because it's using that burp of air more efficiently than your gun roaring like a twelve gauge after the projectile has struck the target..



On what factual data do you base this comment?

"your gun roaring like a twelve gauge after the projectile has struck the target"

How do you model the burp of a hammer valve?


What is the equivalent chamber size?
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Unread postAuthor: Technician1002 » Sun Apr 18, 2010 9:32 pm

My 2 inch cannon was able to move a tire shop air impact wrench from 3 feet away with no barrel. It slid on the concrete floor for about 3 feet.
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