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All in one valve

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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Unread postAuthor: iknowmy3tables » Sun Feb 21, 2010 5:30 pm

I think if the valve is significantly dependent on grease to seal then grease will inevitably seap through at high pressure, I'm really unsure about this , either the cohesive forces will be able to counter the force of pressure, or if I look at the grease a molecularly dynamic it inevitably leaks, man fluid dynamics is really complicated I don't wanna mess with it

hmm I'm thinking you could cut a curved end in a rubber rod using a sharpened pipe, for a rotary valve
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Unread postAuthor: john bunsenburner » Mon Feb 22, 2010 1:49 pm

I wonder, if I had a closed mechanism up top, and an O-ring at the bottom of the spool, inside the casing, wouldn't that prevent the air from leaking out, and the grease from seaping out?

Would you mind elaborationg on your rotary valve idea?
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Unread postAuthor: POLAND_SPUD » Mon Feb 22, 2010 2:36 pm

wouldn't that prevent the air from leaking out, and the grease from seeping out?
what about the barrel port ?

I googled 'metal to metal' seals and this is what I found
http://www.techmasterinc.com/engineerweb/NumaticsSpool/Spool.html

I know I've found something much better on this but I don't remember where
anyway the idea you posted isn't bad but if I were you I'd use o-rings and place the ports on different levels... at least that would let you concentrate on other things that have to be improved there
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Unread postAuthor: john bunsenburner » Mon Feb 22, 2010 2:57 pm

machined to a millionth of an inch...thats out of question. Also what about the barrel port?
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Unread postAuthor: POLAND_SPUD » Mon Feb 22, 2010 3:36 pm

if I had a closed mechanism up top, and an O-ring at the bottom of the spool, inside the casing, wouldn't that prevent the air from leaking out
it could still leak through the barrel port
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Unread postAuthor: psycix » Mon Feb 22, 2010 5:30 pm

When I machined a piston to match the diameter 1/50th of a mm or closer, it was nearly impossible to blow air through. On high pressures it may leak a bit, but tight machining and some grease should be able to seal stuff for short periods.
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Unread postAuthor: iknowmy3tables » Mon Feb 22, 2010 10:37 pm

john bunsenburner wrote:Would you mind elaborationg on your rotary valve idea?

alright, but I'm gonna have to ask for you to explain your need for sealing with grease? didn't you say you wanted to go with poland spud's sort of design, and wouldn't that just use sheet rubber sandwiched between washers?

anyway's so in the aaaa.png picture I pointed out how the profile of the oring does not match the profile of the rotating rod. So to get a piece of rubber that does match the profile of the rod, use a sharpened pipe about the size of the rod to cut a rubber rod like so, and you could also use the threads of the attached fitting to tighten the seal using that method you should be able to construct rotary valves
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Unread postAuthor: POLAND_SPUD » Mon Feb 22, 2010 10:52 pm

wouldn't that just use sheet rubber sandwiched between washers
I don't think that rubber washers would work well there... I wanted to use orings

and once again I really believe that rotary valves are just a waste of time... in many ways they are almost like ball valves and have all the possible disadvantages that they have
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Unread postAuthor: iknowmy3tables » Tue Feb 23, 2010 12:32 am

well there wasn't much rod to put o-ring groves on, and I just saw disks between nuts, well just to let you know it is a way you can make seals and it's adjustable

and yes your opinion about rotary valves has already been noted, but regardless of your opinion it's nice to know how to construct them because it has frequently reappeared in threads
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Unread postAuthor: john bunsenburner » Tue Feb 23, 2010 11:26 am

Well I was thinking that putting grease inbetween the gap between spool and spool housing would make it leak proof, this has apparently been confirmed by psycix.

@poland spud; if I have a confined space for the grease to be in then if any air escapes the pressure of the grease rises, I would hope that in that design the air would only exit a slight bit before the pressure rising too high for it to penetrate further, it wouldn't get to the barrel port.

Now for rotary valves, how do ball valves seal?

Also the performance can be increased by having an O-ring in the spools ammo compartment as stated time and time again. The air flow starts once the projectile clears the compartment, its easy enough...
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Unread postAuthor: POLAND_SPUD » Tue Feb 23, 2010 11:55 am

yeah I know... that's why I said there was a better link on that type of seals but I couldn't find it.. there was really much more info on them and yeah the tolerances were not as close

how do ball valves seal

lol hard to explain in words... but you'd know how hard is to describe them if you dismantle a BV

I didn't think of that... that would require you to put some sort of oring inside the ball to seal it until ammo can leave the valve... on it's own it would be pretty cool and probably quite simple
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Last edited by POLAND_SPUD on Tue Feb 23, 2010 12:27 pm, edited 1 time in total.
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Unread postAuthor: john bunsenburner » Tue Feb 23, 2010 12:02 pm

Well you can modify a BV to do that, making is one of the most efficient valves, but why simple if it can be hard too?

Think a BV sealing mech could be incorporated into a rotary valve?
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Unread postAuthor: POLAND_SPUD » Tue Feb 23, 2010 12:33 pm

john bunsenburner wrote:Well you can modify a BV to do that, making is one of the most efficient valves, but why simple if it can be hard too?

Think a BV sealing mech could be incorporated into a rotary valve?

well it would probably be simpler to mod a BV it into a rotary valve (though technically it probably already is a rotary valve but I know what you meant)

but yeach I guess it can be done... but even if you solve sealing it won't be the most comfortable valve you can imagine
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Unread postAuthor: john bunsenburner » Tue Feb 23, 2010 12:35 pm

Well it would be the simplest semi automatic valve ever designed...

Do you think the inside of the spool housing could be built similar to a BV interior for sealing?
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Unread postAuthor: iknowmy3tables » Tue Feb 23, 2010 4:20 pm

ball valves use balls so the issue I've been trying to address about curved seals doesn't apply, they use something more like rubber washers, and typically they seals push from opposite ends so, however when attempting something like a 3way the ball isn't exactly compressed between the seals from opposite ends, so they typically use rods.

modifying ball valves for a rotary valve purpose is too difficult, the diameter of the hole is too big in relation to the diameter of the ball, the below picture should give you an idea of how difficult it is to mod a the ball
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