What would be the best valve...

[Sparow89]

What would be the best valve for a large caliber cannon/mortar.
I want to build a cannon or mortar for paintball with a 2.5-3" bore, but I cannot decide what the best valve design to go with: co-axial, QEV, etc?

[blind909]

If it is for a stationary mortar, use a union and a Burst Disk (Dont ask, look it up on Wiki).

[Sparow89]

I need a valve that can be repeatedly used and quickly.

[blind909]

A piston valve, or a sprinkler valve.

[Carlman]

QEV can be used very fast

EDIT: didnt see the large bore bit.

you can get a 2" or even 3" sprinkler valves off ebay for cheapish. i just got mine from a trash recycling station for 3$ lol

[blind909]

Yes, you could also use a qev, but for a large bore, a big qev would be alot of money.

[SpudFarm]

a mortar does not need all that much performance.
what about a butterfly valve?

[brogdenlaxmiddie]

a mortar does not need all that much performance.
what about a butterfly valve?

I hearby second that notion.

[MrCrowley]

I'd go with a 3/4" QEV. Like 'Farm said, you don't need that much performance.

But if you do want that much performance, go piston, burst disk or butterfly valve.

[DYI]

Large butterfly valves are reasonably cheap when compared to other valves of the same size, and if you have a kickass servo to open it, performance shouldn't be too hideous. The real problem here is the aforementioned kickass servo - they aren't very cheap.

Your best bet here is a homemade piston valve. A storebought valve of that size isn't cheap, no matter what kind it is. Some variation of the barrel sealing piston valve is the answer to a large number of spudding problems, especially in the "ease of use" area.

[SEAKING9006]

I see the burst disc as a simple, easy to use alternative. Especially if the round slides down the barrel and hit's the breach with a bit of force. If that's the case, stick a tack or a nail to the back and you have a classic mortar.

[psycix]

Co-axial piston valve would be a good choice: compact, easy to use and because of the better performance above a butterfly, you need less pressure for a certain distance. The result: saving more air or CO2 and it is less loud.

[CS]

Given your described circumstances I'd think a homemade piston valve, QEV, and sprinkler valve will all work for ya. A butterfly is going to run you a lot money, and a burst disk has a low ROF (Rate Of Fire).

I would recommend a QEV, but they can be a hassle to get your hands on. As well a sprinkler is relatively similar to a QEV.

A sprinkler valve will work just dandy. There fairly easy to find and cheap. With any luck you find them at Lowes or Home Depot. Comparatively they have less performance then a reasonably sized piston valve, but a mortar isn't a performance demanding cannon.

Now a homemade piston valve will work, but given the option of a sprinkler valve a piston valve seems unreasonable. They can be hard to build, and frustrating. However a coaxial piston valve would allow you to contain your launcher in a single pipe, rather then a over-under design.

I would recommend a sprinkler valve, but if you decide a homemade piston valve could also work for you.

[Sparow89]

I have been considering the Piston valve above all because I am trying to get the best range possible. I am just hoping that the ammo I use will reach a terminal velocity less than 300fps on the way down. It would be awesome if I could reach every corner of the field. I also have an idea for a coaxial breech loader design put that will be another topic once I draw up some schematics.

[MrCrowley]

Piston valve looks like your best bet then, quick, powerful, cheap.

Now you need to work out some specs for the launcher, like configuration, chamber length and diameter, barrel length and diameter, pressure, pressure source...

I'd say a 2" barrel sealing piston valve would be big enough.