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Piston valves

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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Piston valves

Unread postAuthor: nosgroth » Tue Aug 18, 2009 5:43 am

Hello, its my first time here, im 15 and I've had some experience with simple spring actuated ball valve cannons. I have carefully examined innumerable diagrams and pictures of the many assortments of valves and guns (BTB . cough*, Ragnarok. cough*). Anyway. I live in the Uk, London but thats as much as you'll get about my present location, and i have spent well over £300 over the course of 2 years and hard work to make a "T" piston valve. And I haven't even finished it because I cant find materials that can be used as or made into a Piston. I cant make a glue piston (no glue gun or lubrication), neither can I make a wooden dowel piston. So after trying for weeks i have given up 3 separate attempts to make a piston valve and just turn to the stupid old spring actuated ball valve carbine type thingy. Please could a fellow Briton point out to me a place where i could get my grubby hands on a friggin piston.

...May the flying spuds be with you...
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Unread postAuthor: FORE!!!! » Tue Aug 18, 2009 5:50 am

lol at 300 pounds,,,are u making it from solid gold?? :idea:

have u thort of glueing 2 ends caps together,weather pvc or brass??

theres heaps of home made ideas if u just look around..

ps. ill sell u mine for 300 pounds

pps. if ur using a threaded tee of any nominal size,for the piston housing ,take ur threaded nipple and go for a walk downtown and see what fits snugly, if u find some dowel the right diametre all u need is a saw to cut it to size
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al-xg wrote:
I've used various things like cutting oil, silicone lubricant, even butter

jsr wrote:
This collection of containers on your bedside table must look very intimidating to any visiting young ladies

...but hey, lube shows you care;)
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Unread postAuthor: nosgroth » Tue Aug 18, 2009 5:59 am

Thanks for responding,but what about a sealing face for the piston? I've tried the dowel idea and all it does is make a farting sound, and I've tried an end cap but nothing seals!
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Unread postAuthor: FORE!!!! » Tue Aug 18, 2009 6:13 am

idealy u need neoprene ,sheets of it are usually sold at rubber supplies

or u could try using the rubber from underneath ur mouse pad???
maybe even the sealing face on a general household tap washer??


what is the size of the tee you intend on using?
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al-xg wrote:
I've used various things like cutting oil, silicone lubricant, even butter

jsr wrote:
This collection of containers on your bedside table must look very intimidating to any visiting young ladies

...but hey, lube shows you care;)
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Unread postAuthor: jackssmirkingrevenge » Tue Aug 18, 2009 6:57 am

Have you considered the joys of binary adhesives?

If not, a good QEV will give you piston valve performance (because after all, it's pretty much the same thing) and will cost you a relative pittance compared to what you're already spent.
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Unread postAuthor: absinthe » Tue Aug 18, 2009 7:06 am

i used rubber from the seal around a windscreen wiper motor (mainly cause i had it laying around) i have tried using tap seals as the sealing face and it was to hard and just wouldn't work very well...

i did end up using the tap washers as the back of my piston as they fit perfectly into the rear of a 3/4" copper olive male adapter i also used one as the bump stop (i just posted details in the showcase)

http://www.spudfiles.com/forums/viewtop ... tml#256603
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Unread postAuthor: geardog32 » Tue Aug 18, 2009 9:02 am

is it a two inch piston? if so for my piston i just used a 1@1/4 coupling with a 1@1/4 plug and then gave it a rap or two with some smooth wide tape. then for the sealing face i used some old rubber rain boots my girlfriend was going to throw away.
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Unread postAuthor: clemsonguy1125 » Tue Aug 18, 2009 11:06 am

Use a one and one fourth coupling and if you cant find it order it online and for rubber you can order it off amazon and I think you can get the coupling there too
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Unread postAuthor: Biopyro » Tue Aug 18, 2009 11:49 am

This coupling stuff is all great advice but pretty useless - he's in the UK!

As JSR said, binary adhesives will work, or if you drop wildebeers a PM, he may well sell you one which will be no doubt excellent.

I feel your pain, I tried making a 63mm piston cannon but eventually shelved it because of my lack of a good piston and went on to a different cannon.
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Unread postAuthor: geardog32 » Tue Aug 18, 2009 12:09 pm

why is it that anyone in other countries have such a hard time getting materials? i dont know what this is like, but is there a reason behind it. do they just simply not have them, or is it an issue of not importing things.
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Unread postAuthor: Technician1002 » Tue Aug 18, 2009 12:10 pm

For smaller stuff, I have had excellent results using HDPE. It can be turned on a drill press to the correct diameter and then the face can be trimmed while on the drill press to create a true flat seal.

A short picture tutorial is below.
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Attachments
PICT243.JPG
Broken PVC piston sits on a sheet of HDPE
PICT244.JPG
A square of HDPE is cut larger than the required diameter
PICT245.JPG
A hole is drilled into the back of the piston for a support bolt to become an arbor for the drill press. The hole does not go all the way through the piston.
PICT246.JPG
The piston is cut down to size and made round by raising and lowering it past a cutting tool. Here a common wood chisel in the drill press vise works well.
PICT248.JPG
The chisel is passed underneath to finish the face of the piston.
PICT251.JPG
EQ port is drilled from the chamber area to the pilot area
PICT252.JPG
Finished piston installed. To finish, the bumper and breech plug with pilot valve is added.
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Unread postAuthor: qwerty » Tue Aug 18, 2009 12:29 pm

Im from the UK to but B and Q is terrible for threaded parts you should just buy a very cheap glue gun to make the piston out of i think there around a fiver and i use vasaline for lubrication :D
For threaded parts the only way to get them is from a local hardware store or the internet which is the way i go :)
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Unread postAuthor: Willdebeers » Tue Aug 18, 2009 12:49 pm

Biopyro wrote:This coupling stuff is all great advice but pretty useless - he's in the UK!

As JSR said, binary adhesives will work, or if you drop willdebeers a PM, he may well sell you one which will be no doubt excellent.

I feel your pain, I tried making a 63mm piston cannon but eventually shelved it because of my lack of a good piston and went on to a different cannon.


I lol'd at that! Sell him one? Anyway, What size is it? Im doing something for hotwired but I can do something for you and I would be pleased to help.
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Unread postAuthor: nosgroth » Tue Aug 25, 2009 11:59 am

thanks for the feed back guys but remember in 15. Don't get too excited about the various machining methods for pistons. I dont have all the elaborate tools which output extreme precision. I think I'll try a wooden dowel, or a hot glue gun piston. The problem is that I dont have a hot glue gun nor nearopane sealing washers, I was gonna look a week ago, but I went down to the B N Q yesterday but it had moved!!!!!
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Unread postAuthor: Hotwired » Tue Aug 25, 2009 5:32 pm

What I'm interested in is what that £300 got spent on :)

I know this is a fairly wasteful hobby as pipe and tube doesn't tend to come in sizes you want but £300 should go a fair way ^_^

If you want a machined piston you did note that willdebeers offered to help there, he's machined some things for me and he's machined pistons as well. You could get some stock plastic rod and arrange for it to be lathed down for example. He's currently just asking for shipping costs so it's an excellent opportunity for small parts to be made.

Why a piston over for example, a QEV? You could get a 1/2" QEV for £12 delivered. Unless of course you're thinking of a large bore cannon.
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