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Valve trouble:

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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Valve trouble:

Unread postAuthor: judgment_arms » Thu May 15, 2008 4:43 pm

Dang-nab-it, I have the worst luck with valves!
Every last Sprinkler valve I buy leaks, and I can’t even get a piston valve to work right! :x

But that’s not the reason I started this thread, this is:
I’m currently working on a Toolies style piston valve, and I have been for weeks… make that months, over three prototypes I’ve encountered the following problems:
Before I list the problems some general specifications:
All the valve prototypes have been built inside a piece of 1.5 inch SCH40 PVC pipe about a foot long, they have all been 1inch porters, and they have all been made to pilot by simply unhooking it from the gas supply (1/4 inch quick disconnect).
The pistons were made from a piece of all-thread with fender washers and rubber disks for seals.

X1:
Never fully sealed
Open incredibly slow (there was a good delay between pilot opening and main valve opening)
Seal face gets sucked into the barrel port
Seal face ripped

X2: *changes: piston rod .5 inch longer*
Never fully sealed
Seal face gets sucked into the barrel port


X3: *changes: piston rod is a full 2 inches longer then the X1’s in hopes of achieving usable performance and back of valve has a threaded adapter to permit access to piston*
Doesn’t open
When it does it has very little power.


I’ve experimented with everything from neoprene washers to gasket material to leather washers for seal faces, nothing works.

On average pilot volume is about 2in^2.

Here are pictures of the X2:
Parts layout:
Image
Piston:
Image
Completed and glued:
Image


I’ll get pictures of the X3 later.


Any help or advice would be very much appreciated.
Thanks All! :)
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Unread postAuthor: psycix » Thu May 15, 2008 5:03 pm

You seem to have problems with your sealing face...
Did you already try the good old inner bike tube? (atleast two layers)
More layers make it able to be pressed in further, making up for inconsistencies.
Does the barrel port it seals against have a tapered edge? A bit like a spudcutter, but not so sharp.

Your sealing faces get ripped off...
How do you secure them? With just a nut or also an as big washer possible?
Make sure to tighten it DAMN HARD

You also seem to have pilotting problems.
I suggest a larger pilot valve, that should solve the most of it I think.

Also, does the back piston washer seal good enough?
Can air leak past it form the chamber into the pilot??
Make it seal better, OR get one hell of a pilot valve to overcome this.



Hope this helps you :D
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Unread postAuthor: judgment_arms » Thu May 15, 2008 6:20 pm

psycix wrote:You seem to have problems with your sealing face...
Did you already try the good old inner bike tube? (atleast two layers)
More layers make it able to be pressed in further, making up for inconsistencies.

No, the only inner tube I have is dry-rotted, but at one point in time the X3 had a neoprene washer, two layers of gasket material, a leather washer, and another disk of gasket rubber; it sealed but the outermost layer got sucked off the end of the rod…

Does the barrel port it seals against have a tapered edge? A bit like a spudcutter, but not so sharp.

X1: no
X2: sort of
X3: yes

Your sealing faces get ripped off...
How do you secure them? With just a nut or also an as big washer possible?

As big of washer as I felt I could safely use with out it interfering with sealing.

Make sure to tighten it DAMN HARD

If I tightened it any it would have ripped the gasket, I know this from experience. :roll: :)

You also seem to have pilotting problems.
I suggest a larger pilot valve, that should solve the most of it I think.

Well that’s just it, I was trying to avoid having to go to a larger pilot valve…

Also, does the back piston washer seal good enough?
Can air leak past it form the chamber into the pilot??
Make it seal better, OR get one hell of a pilot valve to overcome this.

Since the back piston is made up of a stack of washers alternating between steel and rubber it can make it as tight as necessary, on the X1 it was in there a bit on the loose side, the X2 I think it’s just right, and the X3 it’s adjustable.


SHE LIVES!!!
I was lookin’ at the X3 when I went to take pictures and I noticed that the piston slid in and out relatively easy, low and behold I had forgotten to tighten up the washers; after hunting up a wrench and tightening them up it now opens with a rather nice POW! :D

It still doesn’t seal to good, I’d say it’s about an 80-95% seal, right know the seal face is a neoprene washer with a piece of gasket on top, I super glued the neoprene to the fender washer and the gasket to the neoprene to prevent it from being sucked through.

Give me a minute and I’ll have picture up for you to look at…

Thanks Psycix! :D
EDIT:
Finally got the pictures of the X3:

Piston assembly:
Image

Piston:
Image

Seal face:
Image

Valve body:
Image

Valve body cap:
Image

Inside of valve cap:
Image

What do y’all think?
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Unread postAuthor: socoj2 » Thu May 15, 2008 7:56 pm

Want to buy an Asco?

use a larger washer to reduce the total amount of Material that is exposed to the sealing face.
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Unread postAuthor: judgment_arms » Thu May 15, 2008 8:51 pm

socoj2 wrote:Want to buy an Asco?


how much, and what size?
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Unread postAuthor: xboxteen01 » Thu May 15, 2008 10:37 pm

how does this valve work. i understand the piston concept, but is the valve body also the chamber? could someone post a pic of a gun that uses this style of piston valve?
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Unread postAuthor: judgment_arms » Thu May 15, 2008 11:01 pm

xboxteen01 wrote:how does this valve work. i understand the piston concept, but is the valve body also the chamber? could someone post a pic of a gun that uses this style of piston valve?


Take a look a Jackssmirkingrevenge’s pneumatic cartridge designs, or the Toolies piston.
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Unread postAuthor: psycix » Fri May 16, 2008 6:05 am

Thanks Psycix! :D


Your welcome :D

Another thing popped into mind: it still leaks eh? Maybe the sealing face seals perfect, BUT it leaks trough the center where the nut is.
Maybe a lil bit of bike tire between the nut and the washer that holds the sealing face could overcome this.
Another way to overcome it is to tighten the stuff even MORE DAMN HARD :wink:


I suppose shouldnt have to tell you this, but ill do to be sure: the pipe it seals against should be cut square, and that your sealing face has to be like that too. Maybe that when youve tapered the pipe edge youve accedentically made a dent into the pipe end?


Note that superglue may not be strong enough, sealing faces wich are glued tend to rip off in one shot. Since yours also has a washer+nut this probably wont happen, but it may.
[/rambling out information that might be useful to you someday]
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Unread postAuthor: jrrdw » Fri May 16, 2008 8:37 am

Another way to combat the sealing washer from ripping off is to use a steel washer on top of the sealing rubber washer the same size of the inside of your barrel. That way the only rubber exposed has little to no chance of being sucked into the barrel. Thats what I did with The Basterd from the start so that I wouldn't have to deal with this type of problem.
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Unread postAuthor: judgment_arms » Fri May 16, 2008 9:22 am

psycix wrote:Another thing popped into mind: it still leaks eh? Maybe the sealing face seals perfect, BUT it leaks trough the center where the nut is.

*slaps self in head* I forgot the Teflon tape over the holder washer and on the rod…

Maybe a lil bit of bike tire between the nut and the washer that holds the sealing face could overcome this.

No bike inner tube, remember. ;)

Another way to overcome it is to tighten the stuff even MORE DAMN HARD :wink:

As I said, if I tighten it to much it’ll rip the gasket material, trust me I done it before… :roll:


I suppose shouldnt have to tell you this, but ill do to be sure: the pipe it seals against should be cut square, and that your sealing face has to be like that too. Maybe that when youve tapered the pipe edge youve accedentically made a dent into the pipe end?

It better be square, I spent three hours squaring and honing the face…

Note that superglue may not be strong enough, sealing faces wich are glued tend to rip off in one shot. Since yours also has a washer+nut this probably wont happen, but it may.

I figured super glue would be better than rubber cement, and I couldn’t find my Goop…



jrrdw wrote:Another way to combat the sealing washer from ripping off is to use a steel washer on top of the sealing rubber washer the same size of the inside of your barrel. That way the only rubber exposed has little to no chance of being sucked into the barrel. Thats what I did with The Basterd from the start so that I wouldn't have to deal with this type of problem.

I couldn’t find any washer that would fit “perfectly” so I ended up using what I could, which is obviously too small.
Someday soon I’m going to chuck a fender washer into the drill press and turn it down to the appropriate size.


Thanks All!
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Unread postAuthor: psycix » Sat May 17, 2008 2:46 pm

Keep us up to date when youve got news. :)
Good luck :D
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Unread postAuthor: microman171 » Tue Jun 17, 2008 1:13 am

I am thinking of making a gun just like this and I was wondering how the barral on this works? I cant actually see it...
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Unread postAuthor: judgment_arms » Tue Jun 17, 2008 7:47 am

microman171 wrote:I am thinking of making a gun just like this and I was wondering how the barral on this works? I cant actually see it...

Well, that’s probably because there is no barrel on it yet. ;)
The barrel attaches to the side with the 1” female adapter, in the picture entitled “Valve Body” it’s the right hand side.
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Unread postAuthor: DonTheLegend » Tue Jun 17, 2008 9:32 am

Looks like you managed to solve your problem for the most part but another way to seal the face of the piston is with an O-ring. If you can find one that fits tightly inside the pipe and place it up against where your piston would seal and hold it in place with some silicone or something similar. Then just let your fender washers press against it. Did this on my last gun, this crush seal works quite well if you can find a suitable o-ring.
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Unread postAuthor: judgment_arms » Tue Jun 17, 2008 9:53 am

Humm… DonTheLegend, you just gave me an idea…
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