SpudFiles

the behind piston filling seems like it would work better to me, but joel's supah valve uses in chamber filling, which ones better???

behind piston filling:
http://www.advancedspuds.com/valve2.htm

in chamber filling:
http://spudtech.com/detail.asp?id=31
or any of the other cannons that use the supah valve

There's not one that works better than the other, it all depends on how you make the valve. Why do you think that one is better then the other?

it just seems that there is less room for error in the behind piston filling one. I am currently making one (modelled after the supah valve and is chamber filling) and i'm questioning the power of my spring and will it be able to hold back 100 psi (or 680 Kpa [kilopascals]).

ps. I'm from Canada and I like the metric system.

The only difference from the two is that the chamber-filling one requires a spring, while the behind-piston one does not. I personally like the behind-piston one because it does NOT require a spring. It also seals more reliably, but this factor can be eliminated if the piston valve is constructed properly (as in a supah valve)

Give a few more details on your valve; maybe we can help

Your spring shouldn't be holding back pressure at all. It should be air pressure that holds the valve closed, which is how all valves work (excluding ball valves) even sprinkler valves use air pressure to hold the valve closed. I think you might need to revise your valve design.

You should take a look at this animation explaining piston valves.
http://forums.spudtech.com/topic.asp?TOPIC_ID=13265

yes I have seen that many times, sry I should have made myself more clear. I meant i'm worried that my spring won't be able to hold back (during the filling process) if I make my hole to small.

ps. the model shown on that link is a behind the piston filling valve, i'm talking about when you fill it from the chamber.

when you fill it from the chamber it makes more sense because less air has to go through the little hole because the pilot area is smaller but if it fills to fast then couldn't the hole be too small and the piston push back???

i'm talking about the supah valve style, do you know how that works??? with the piston sliding on a guide with a spring behind it

Ya, I've seen supah valves. I don't think you need to worry about the spring holding the pressure while filling, you'll be amazed how fast air can get thought even tiny holes. You should be fine, if the valve doesn't equalize fast enough you can always make your equalization hole larger. I also agree that a supah style valve would probably fill a lot faster. I don't think that it would offer any more power as far as shooting is concerned.

thx, i'm still going for the supah type valve (the guide that blocks off most of the hole is whats bothering me) but I have to go into my dads shop at work to build the piston so I have a lot of time to think about things. Also seeing as this is my first pneumatic and 2nd spudgun I have changed my plans a million times from a ball valve to sprinkler valve to barrel sealing to chamber sealing piston. I have gotten a lot of help from this site and besides spudstuff, everyone has been really nice.

do you have a lathe at your dads shop? ive done the same thing as you lol ive changed my valve like 6times and 1month later im actually building one.

yeah he's got a lathe but hes not very good with it. He knows this guy who comes in and does personal projects on the weekend so i'm hoping hes there next weekend to help me out *crosses fingers* if I can even go next weekend *crosses fingers tighter and makes a wierd face*

can you just explain WHY you switched from a barrel-sealing piston valve to a chamber-sealing piston valve? Barrel-sealers are easier to make and they yield greater performance, not to mention that they have less dead space (if you make them right)

You could make the hole relatively big and put a check valve in it.

Rmich is right. Barrel sealing vavles have been proven to perform better. And I think that they are simpler too.

And you don't need O-rings for BSP

why does joel use chamber sealing then????