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Help with what type of piston valve to use??

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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Help with what type of piston valve to use??

Unread postAuthor: jazzman56 » Mon Jun 20, 2011 8:15 pm

I have recently been researching on building a steel tennis ball cannon with a PVC barrel, for an a school assessment.

I have limited facilities (only a hardware store a backwoods catalog and basic tools). I am wanting to know what would the best and easiest piston valve to build e.g barrel sealer.

Should i build:

MRR's Self closing piston valve:
http://www.spudfiles.com/forums/self-closing-piston-valve-brass-fittings-t17609.html


1. How does MRR's self closing piston work????

2. What type of rubber to use, will an bicycle inner tubing do ?? ( Maybe from Crazy Clarks )

3. Where do i get the sealing gaskets????

or a hot glue or epoxy piston


1. What is an equalization hole???

2. How to mold it??

The barrel will be a 65mm pressure rated PVC barrel
The accumulator (pressure vessel) will be made of section of 50mm galvanized steel pipe
Filled by and brass schrader valve
triggered by a 3/4 ball valve (brass or nickel)

I would like to try and make the piston out of brass fittings that are readily available at Bunnings

Any links to how to's are welcome

Note: I have already built a ball valve air cannon out of pressure rated pvc with a 4cm by 55cm accumulator a schrader valve and a 3/4 (2cm) inch ball valve with a 2cm barrel.

Thanks jazzman56
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Re: Help with what type of piston valve to use??

Unread postAuthor: jackssmirkingrevenge » Mon Jun 20, 2011 8:30 pm

jazzman56 wrote:1. How does MRR's self closing piston work????


Like any other piston valve. http://www.spudfiles.com/forums/piston- ... t8157.html the spring in the pilot area helps it close.

2. What type of rubber to use, will an bicycle inner tubing do ?? ( Maybe from Crazy Clarks )


That would be a bit too thin, try truck tire inner tube :)

3. Where do i get the sealing gaskets????


Try the plumbing section

or a hot glue or epoxy piston


Now you're talking!

1. What is an equalization hole???


Equalises pressure between chamber and pilot - unless you piston is 100% airtight, you don't need one.

2. How to mold it??


All you need to know here:

http://www.spudfiles.com/forums/making- ... t8919.html
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Unread postAuthor: Technician1002 » Mon Jun 20, 2011 8:34 pm

Tennis ball launchers take a big performance hit with small valves. You can launch a tennis ball further on 20PSI and a 2 inch valve than you can at 70 PSI and a 3/4 inch valve.

In larger sizes epoxy or hot glue is not recommended. A bare minimum size would be 1 inch. 1.5 to 2 inch makes a huge difference.

How far are you intending on launching a tennis ball?
http://www.youtube.com/watch?v=s0l5t7D0FDM&
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Unread postAuthor: Crna Legija » Mon Jun 20, 2011 8:58 pm

you should use this how to. but dont use pvc from bunnings its not pressure rated and unsafe you would have to go to reace.
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Unread postAuthor: jazzman56 » Mon Jun 20, 2011 9:07 pm

jazzman56 wrote:saefroch

True, i need to control all the variables and the speed the valve opens needs to be controlled. I just need to find all the parts a for MMR's piston in a larger size. SO the epoxy piston can't go over how many inches/centimeters, and why is this so?

Also what is the best way to pressurize this unit (with a bike pump as a don't have an compressor). Thinking of using a brass schrader valve.

Thanks for tips

jazzman56 wrote:Would a quick dump valve be better as in Technician1002 tennis ball cannon

jazzman56 wrote:Also bunnings doesn't sell pressure rated pipe above 4cm.

So that's why i am going with steel.

Is it best to make the piston housing out of steel or brass???

jazzman56 wrote:Or would a ball valve attached to a spring and trigger system also work??

I need a simple piston valve to make otherwise my science teachers head will cave in. The experiment is not on the cannon itself but how the distance of tennis ball changes due to the weight of it.

So i need a piston valve that will still open at low pressures etc 20psi.

EDIT::::Sorry, didn't know that the edit button existed.

I can find a brass schrader valve on ebay
Where do i put the schrader valve in relation to the piston and how to trigger it. example: do i have a ball valve to a T fitting that has the schrader valve in the other end of the T then connects to the piston housing

EDIT: My head is gonna cave in, I need a easy valve to build that will keep the opening speed constant and that i can build with parts i find at a hardware store (Bunnings).

EDIT: With the piston valve do i put the bolt in after the epoxy has set or put in place before the epoxy has been poured in.
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Unread postAuthor: saefroch » Mon Jun 20, 2011 9:08 pm

I'd go with the piston valve. Even if the flow difference is minimal (which is unlikely, the piston valve should be quite better), a piston valve is far more reproducible than a manually operated ball valve.
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Unread postAuthor: jazzman56 » Mon Jun 20, 2011 9:12 pm

saefroch

True, i need to control all the variables and the speed the valve opens needs to be controlled. I just need to find all the parts a for MMR's piston in a larger size. SO the epoxy piston can't go over how many inches/centimeters, and why is this so?

Also what is the best way to pressurize this unit (with a bike pump as a don't have an compressor). Thinking of using a brass schrader valve.

Thanks for tips
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Unread postAuthor: saefroch » Mon Jun 20, 2011 9:22 pm

To connect to a bike pump I suggest taking a bike schrader valve, cleaning all the rubber off it and then soldering it into a brass 1/4"-1/8" bushing. At least that's what I did. If you can find one with threads on it already that'd be best, but I've never found one at my local hardware stores. Or are you asking about something else? The question seems unclear...

Personally I see no reason why one wouldn't make a large epoxy piston, but I know hot glue will deform too easily.

At the pressures you're running, the material doesn't really matter, but I've always used a brass fitting for the piston housing because they're usually seamless, as opposed to galvanized steel fittings which typically have a weld down the inside.

Please use the edit button.

EDIT: USE THE EDIT BUTTON!

A QDV's benefits over a traditional piston valve are generally insignificant, but you will see some significant benefits at low pressure. The only trouble with a QDV is they can't be built with typical plumbing supplies, and so far the only QDV housings that have been built required welding or brazing (I think, don't know about BtB's, if that's even a QDV).

Your teacher's head will not cave in over a piston valve...
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Unread postAuthor: Crna Legija » Mon Jun 20, 2011 10:02 pm

Well any bunnigs iv been in dont have pressure rated pvc. Maybe where in diffrent sates
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Unread postAuthor: Technician1002 » Mon Jun 20, 2011 11:19 pm

jazzman56 wrote:Would a quick dump valve be better as in Technician1002 tennis ball cannon


Even a large 2 inch ball valve would be better. It opens slower, but flows much better.

From your listing of the tools and supplies, I don't think you are ready to try a QDV.
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Unread postAuthor: jackssmirkingrevenge » Wed Jun 22, 2011 7:11 am

Technician1002 wrote:In larger sizes epoxy... is not recommended.


Objection!

See my notes on built-up pistons in the epoxy pistons how-to.

Have you considered using a burst disk? It will give you unbeatable performance with a chamber that can be filled using a blowgun or similarly shitty valve, the only disadvantage is having to change disks and a slight delay between valve opening and firing. It all depends on intended use.

Here's a diagram of how it might look:

Image

Note the cam-lock can be substituted with a union and air feed can be anything depending on what you have available.

You might also consider making a simple combustion, for large bores you will get great performance with a relatively unsophisticated and cheap design, especially compared to a pneumatic of equivalent performance.
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Unread postAuthor: jazzman56 » Thu Jun 23, 2011 2:25 am

jackssmirkingrevenge

Thanks for the burst disk idea. The cam-lock should not be a problem (which type??? the catalog i have has 50 types in it.). Would adding a back up ball valve to the design work so as if the burst disk gives inconsistent results. (the force applied to the ball needs to be controlled)

What do i use for a burst disc that will give consistent results. Foil, milk bottle plastic???

I can't make a combustion launcher as it is using an explosive fuel, e.g butane/propane. Which is not allowed in this design.
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Unread postAuthor: saefroch » Thu Jun 23, 2011 10:47 am

Aluminium foil is a common burst disc material, and is useful because it's thin so by adding more layers you can adjust the bursting pressure.

The burst disc will not give inconsistent results unless you have very high flow through the input valve.
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