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DSTV - Save the birds, ban the (blow)guns

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: dongfang » Sun Jul 29, 2007 2:36 pm

Hi,

I have a rather large pilot volume on my new piston valve in construction (75 mm tee).

Spud Yeti, that's a nice idea too. I suppose you want to have a stop for the trigger piston preventing the spring from pulling it in too far.

Well I thought of something like that, then I realized that with, say, a 20 mm port size and an 8 bar pressure, you get like 250 Newtons of force for the spring to hold. That's going to be one big spring, and when pulling it open, it will be you who has to supply the > 250 N as the pilot pressure drops. Would be a silly way to get hurt with a potato gun - pulling it off from the stand and onto your foot :cry:

Then I thought of 2 pistons balancing each other, and both popping open. That's the design I presented.

Regards
Soren
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Unread postAuthor: spud yeti » Mon Jul 30, 2007 8:48 am

Hmmm, yes, good point. I now see why you did that design.
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Unread postAuthor: drac » Mon Jul 30, 2007 9:02 am

I'm not sure where you drew the inspiration for this, but this might help you with designing it.

http://antennalaunchers.com/dftv19/
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Unread postAuthor: dongfang » Mon Jul 30, 2007 8:34 pm

Hi drac,

Ooooooooooooh yeah I have seen he DFTV. I even wrote in this thread that I originally wanted to build one, but my design was flawed (if I put it together one piston would have no room to move). I came up with this as an emergency solution...

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Soren
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Unread postAuthor: mobile chernobyl » Tue Jul 31, 2007 7:18 am

In the diagram on the first page, whats to stop the air from only taking the path of least resistance - the pilot exhuast. It looks like it could easily just all drain out the back unless you put a third seal in the middle that engages at firing point on the rear spool body. spool valves can be fun, for this project if you have the availability to one, i suggest using a lathe and some uhmw with some good o-rings. Your going to need the precision to seal this type of valve, especially with only one o-ring at each location. gluck
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Unread postAuthor: dongfang » Tue Jul 31, 2007 4:21 pm

Hi MC

The air is supposed to take both paths out. It's not a gun main valve. It's a valve for triggering that.

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Soren
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Unread postAuthor: dongfang » Wed Aug 01, 2007 11:18 am

Here are the pieces so far.

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Soren
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Unread postAuthor: Gepard » Wed Aug 01, 2007 11:29 am

The piston a turned part?

Michael
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Unread postAuthor: spud yeti » Wed Aug 01, 2007 12:16 pm

Wow, thats looking really good so far, is the piston shaped from the use of a lathe? Great work so far, I like your style of construction (neat, clean, professional etc)
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Unread postAuthor: dongfang » Wed Aug 01, 2007 1:48 pm

Hi

Thanks.

Hehe, again I can really recommend the mill table from Dremel. It's not even that expensive (maybe you can get it for 25$ in the US??) For groove cuts on the round surface of cylindrical things, you can come a long way with that. You just hold the item against this adjustable guide thing on the table (What is the proper name of it?) and slowly turn it.

I made 2 piston valves with 2 o-rings each and this thing using only that, plus hand tools (nothing beats a nice, large set of quality files).

Oh, and the bolt thing here is not made in one piece, oh no oh no. It's 2 * 20 mm endcaps with 2 * 16 mm endcaps glued into them. And a 16 mm pipe. Next time I will make the pistons a little longer so the pipe has some more stuff to hold on to.

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Last edited by dongfang on Wed Aug 01, 2007 2:03 pm, edited 1 time in total.
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Unread postAuthor: spud yeti » Wed Aug 01, 2007 1:55 pm

Luckily my good friends dad has a lathe and milling machine all in one, so I can use his (I only found this out 3 days ago though). I need to cut O-ring grooves for my one piston (4 of them!) so I will be paying my friend a visit... :D
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Unread postAuthor: dongfang » Wed Aug 01, 2007 5:07 pm

Hey,

How to stuff 4 o-rings into one valve?

(if you use o-rings as a bumper they won't need grooves, ha ha ha...)

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Unread postAuthor: spud yeti » Thu Aug 02, 2007 9:10 am

Haha, no, I need them to seal my piston (you'll see when I post my cannon) so I have to cut grooves into PVC and epoxy. Do they work well as bumpers?
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Unread postAuthor: dongfang » Thu Aug 02, 2007 4:18 pm

Hi,

I have no idea. I´d think they are a little hard for that.

What do you epoxy wrt an o-ring groove?

BUT I found some the other day for DWV. They were made of some neoprene like stuff, and were nice and thick. They could make excellent bumpers - but they don´t fit into my valve.

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Unread postAuthor: spud yeti » Thu Aug 02, 2007 11:50 pm

What do you epoxy wrt an o-ring groove?


I cant get PVC rod, so I fill PVC with epoxy, then make the groove, not exopy the O-rings! (sorry for misunderstanding)

The DWV fittings that are square on the top and about 2mm thick? Yeah, two of those together would work nicely.
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