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Homemade DCV

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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Homemade DCV

Unread postAuthor: Gun Freak » Fri Apr 16, 2010 4:00 pm

I drew this up today... Might make one just because I can't get any DVC's around here. I already know the pilot volume would be kinda big, but that's why I reduced it to 1/4". Discuss.

EDIT: Sorry I forgot to draw an o-ring on the far left side so when it is pressed no air from the compressor gets in. Updated the drawing.
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Unread postAuthor: twizi » Fri Apr 16, 2010 4:03 pm

looks good
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Unread postAuthor: ramses » Fri Apr 16, 2010 4:18 pm

there are other ways. this one reduces part count, ports, and pilot volume.

yes, the drawing was done in paint in around 30 seconds.
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Unread postAuthor: POLAND_SPUD » Fri Apr 16, 2010 4:20 pm

I think it would be easier to build an unbalanced valve, like this one -> http://www.spudfiles.com/forums/5-qev-a ... 20674.html
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Unread postAuthor: Gun Freak » Fri Apr 16, 2010 4:21 pm

The only problem I have with that design is getting the right materials. What would the main body be made of? And what kind of connections would come off of it? You can just tap a nipple or adapter straight into it, bacause that would interfere with the spool (it IS called the spool, right?). I'm kinda newbie with the more complex guns. That design was what I was thinking of before I took into account the ports. Thanks for the replies.
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Unread postAuthor: POLAND_SPUD » Fri Apr 16, 2010 4:32 pm

well you can build a simple DCV like the one in iknowmy3tables' post from a 1/4" T (preferably one with male threads)

make sure that the inside of it is perfectly smooth... then get a bolt or threaded rod, a couple of washers and an o-ring to build the part that slides in it... then add a couple of fittings and that's it

I've never built one but it's an interesting design as it has some advantages that I listed in the thread

the biggest disadvantage is that fact that it it's not balanced but you can always find a way to overcome this problem (like using a lever)

EDIT
pic added
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ohh don't forget that you have to find a way to stop the 'spool' from falling out
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Unread postAuthor: Gun Freak » Fri Apr 16, 2010 4:38 pm

Thanks Poland, I'll check it out.
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Unread postAuthor: Technician1002 » Fri Apr 16, 2010 6:10 pm

In the original drawing, it is assumed the air can only cross through the holes in the dowel. This incorrect. Without a seal between the source and chamber, that path will leak past. Same is true for the chamber to the exhaust. A dowel does not make a ball valve seal between both sides.

ramses is close, but needs the exhaust port moved over to one end. The ports in the dowell need lengthened so in one position the inlet to pilot are connected in the middle the pilot is sealed, and at the other end the pilot is vented to exhaust.

Poland spud needs to look at the force on the end of the spool from the source air. You have to push against the source air to fire it. A mechanical failure will launch the spool out. Designs with not pressure on the ends of the spool work the easiest unless the pressure on the end of the spool to cause rapid motion is desired such as the QDV. Having a mechanical stop on the design would work nice as the valve would remain on supply air until forced to fire. The force on the spool would limit the size to lower pressures and smaller diameters.

The design for Spudtech's propane meter would be perfect. Inlet on one end, exhaust on the other and pilot in the middle. Somewhere in the forum is a drawing of that meter. It moves easily and would do the job with the center tapped to the pilot and the overall length shortened to reduce pilot volume.

EDIT; Dug and found the drawing. Fuel would be air supply, chamber would be exhaust, and the center would have a port to the pilot. Meter volume can be drastically reduced.
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Unread postAuthor: POLAND_SPUD » Fri Apr 16, 2010 6:30 pm

yeah I know but this is the simplest design I can think of... and, as I pointed out myself, it is unbalanced (which has some advantages)

this thing can be built without using any tools... but it goes without saying that in case you have access to machining (though I guess that even a powerful drill press would do) you can directly copy the design used in most commercial DCVs
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Unread postAuthor: Marffy » Fri Apr 16, 2010 6:36 pm

Technician1002 wrote:Image


I just drew up a picture very similar to that, but mine only had 3 o-rings, greatest thing about it: it can be semi-auto!
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Unread postAuthor: Gun Freak » Fri Apr 16, 2010 6:37 pm

Tech, I fail to see how that design would work... as the connection to the air is cut off when the spool is pushed forward. Or am I missing somehing? And Poland, you design seems very prectical... I couldn't find the thread on it though.
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Unread postAuthor: POLAND_SPUD » Fri Apr 16, 2010 7:01 pm

it's the one in my first post here -> http://www.spudfiles.com/forums/5-qev-a ... 20674.html

the thing that technician has posted is a meter... you can put a port in the middle and what you'd get would be pretty much what commercial spool valves look like...
in that particular design there is no 'middle' port as the guy didn't need it (the volume between the two pistons/seals/whateveryoucallthosetworectangualrthings is the metered volume)

@marfy
sorry I could have posted a pic showing what typical spool valves look like in my first post but I assumed you've seen them earlier... lots of people post them and you can see it in the animation I posted in the thread on the semiauto MKIII and on DCVs... ohh BTW you can also find a few pics in some of the links posted there

ohh and you don't need 3 o-rings... two would be enough... and yes you are right you could use that thing as both the pilot valve and the main valve at the same time

However, the most important thing if you want to use a 3 way as teh main valve is to ensure that the valve opens fast enough... most indirect acting valves open relatively fast, as they have a smaller inbuilt piloting valve that switches the spool...

You can also design a valve that would be balanced in one position but as it begins to move it becomes unbalanced and speeds up its own opening... damn I know it's damn hard to understand this without a pic but it is a fairly simple concept
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Unread postAuthor: Marffy » Fri Apr 16, 2010 7:43 pm

i actually haven't seen any "spool" valves? i thought the valve i designed was a first, but then i found out it wasn't :shock:
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Unread postAuthor: Gun Freak » Fri Apr 16, 2010 7:58 pm

Ahhh I understand now. Thanks for the clearification Poland Spud. What kind of materials would be used in the construction of this?
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Unread postAuthor: POLAND_SPUD » Fri Apr 16, 2010 9:13 pm

What kind of materials would be used in the construction of this?

use your imagination... PVC is ok but it won't handle high pressures... metal is better

if you have access to machining you can machine valve body out of an aluminium block.... or you can improvise with standard fittings

probably the easiest way to build the spool is to use threaded rods/bolts and washers


If you have a thick walled tube with an ID of ~5mm.... you can cut it to size, then drill 3 ports in it and use a tap to thread them... then assemble the spool from a bolt & washers... and voila! you've got a 3 way valve
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