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My First Pressure gun ever. Over/Under Design, need help.

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: Yukondano2 » Tue Nov 23, 2010 6:15 pm

Fascinating Saefroch.
http://www.youtube.com/watch?v=75O71AHTIr4

I found this and it seems quite helpful. I just... don't have a hole saw to make a piston :l. Jigsaw MIGHT do it though.
Anyways, now that i think about it, I might want to do a chamber sealing piston. It seems relatively simple so it shouldn't be an issue. Other than i want to use Metal this time. Only issue with THAT is that i don't have anything that pressurizes about 160 PSI. :l

http://www.youtube.com/watch?v=vmxaI3_SJCg&feature=related

Sweet, how to make a metal piston. Will this thing even work well? I mean the piston is made of hot glue.
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Unread postAuthor: saefroch » Tue Nov 23, 2010 6:35 pm

Need to get past 160psi? You can look into acquiring and hooking up a fridge compressor, or you can make your own pump, or you can buy a very high pressure pump. Depending on the diameter of the pump head, you can reach very high pressures with just a small-diameter floor pump.

Yukondano2 wrote:Other than i want to use Metal this time. Only issue with THAT is that i don't have anything that pressurizes about 160 PSI. :l
Just because you can, doesn't mean you have to.

Do not forget this url: http://www.mcmaster.com/ and you can find almost anything you want that related to spudgunning.

The first video makes a very good point, if you build a piston valve, make sure you can do maintenance on it. If your piston breaks, fails, runs out of lubricant, or otherwise has a problem, you don't want to be cutting up your gun. He does a pretty good job explaining piston valves too, I'm rather impressed.

Metal pistons are not usually advisable, except at very high pressures where piston weight is a negligible factor in valve opening time. Hot glue pistons are pretty shock-absorbent and lightweight. It's a pretty good piston material for pistons, but at high pressures you need a pretty good stop to prevent it from breaking.

OMG!!!!!!! That second video is the one I used to make my first piston valve!!!!!! :D :D :D
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Unread postAuthor: Yukondano2 » Tue Nov 23, 2010 6:52 pm

Really? EPIC! I'm going to assume its good then. MRR Makes good videos. Anywho, how is this piston HEAVY? its hot glue, a piece of rubber and a screw. Sounds lightweight to me. :D
I don't want to use Mcmaster because I would rather not give them credit card information, I've never heard of them, so I can't really trust them. That and its... less my choice. I'm 13 so its REALLY the choice of my dad.

The other reason I'd prefer to use metal is because its stronger. I'm not very confident in this plastic. I've dropped pieces of the gun I'm going to put together later today already. Bits of pipe I've dry fit have some decent ridges in them due to the fact I had to remove them with a vice grip.
And lastly, Metal looks awesome.

Btw, do i just have to screw everything in with Metal pipes? I'm assuming there isn't Metal glue, and i don't have a welding torch. The threads on these metal pipes can hold to high pressure, IE using them while still being able to work on it in case the grease runs out.

Can't wait to finish the one I already made though.
*starts dancing*
-EDIT-
http://www.google.com/products/catalog? ... BsQ8wIwAA#

Rather not make a fridge compressor, would something like this work? WEE bit pricey. I'm worried it won't work though. I don't want a tank ( :) Obviously :) ) So this should work.

-EDIT2-
Strange question, I'm not annoying anyone am I? :wink:
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Unread postAuthor: saefroch » Tue Nov 23, 2010 7:14 pm

Not that piston, but
Yukondano2 wrote:Sweet, how to make a metal piston.
That would be heavy.

Real pity your parents won't trust McMaster. The company my father works for purchases from them, so it wasn't hard to convince them to submit their payment info.

PVC can hold a lot of pressure, but not if you're dropping it and damaging it in a vise. That's why I've never built anything out of PVC.

You can build a pipe out of copper by soldering it together, but that's not exactly easy to do maintenance on. The other metal option that I know of is using threaded connections. All threaded connections should have teflon (PTFE, or polytetrafluoroethylene) tape applied to the male threads before putting them together (Hint: point the threads to your right, and tape clockwise looking from the right end). They should then screwed together and tightened very well. If you forget to put teflon tape on, it is likely that the connection will not seal and you will not be able to unscrew it at a later date.

Whoa... nice find on the compressor.
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Unread postAuthor: Yukondano2 » Tue Nov 23, 2010 7:22 pm

saefroch wrote:Whoa... nice find on the compressor.


Thanks :D :D :D :D
Anywho, I might order that. I don't see a Shipping cost. However, I'll do that AFTER I build the gun. Considering that a compressor is REALLY the last thing I need. By Metal piston, I didn't mean a piston made of metal. I meant as in a piston surrounded by metal. As in, to be used in a Copper gun or something. Not in a PVC gun, As like you appear to, I don't want to use PVC if I can avoid it. The breaking thing like you said, the scratching, the fact that it bends so you have to build a wooden brace, metal is actually MEANT to be pressureized, and as I said.
It looks AWESOME

I'll finish my PVC gun as soon as I get my dad to cut with a jigsaw. Btw WHAT could i buy on McMaster that I can use in my gun? Hard to browse for anything there. Personally I like what I found to buy on amazon. 300 Psi :D

I'm going to start designing on Gmod. Should be able to get a screen shot of my idea.
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Unread postAuthor: saefroch » Tue Nov 23, 2010 7:28 pm

All the pipe fittings, valves, flow controls, regulators, compressors, and other building materials you can ever imagine are on McMaster (except the ones you'd be better off making yourself). Just go to their home page, and search "pipe" and pick a material you like. Once you get used to it, the site is really easy to navigate.

You could also give us a link to an uploaded file so we can see your entire design. :wink:
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Unread postAuthor: Yukondano2 » Tue Nov 23, 2010 7:28 pm

saefroch wrote:All the pipe fittings, valves, flow controls, regulators, compressors, and other building materials you can ever imagine are on McMaster (except the ones you'd be better off making yourself). Just go to their home page, and search "pipe" and pick a material you like. Once you get used to it, the site is really easy to navigate.

You could also give us a link to an uploaded file so we can see your entire design. :wink:


Well if you happen to have garrysmod that would work fine.


My idea is to have 3 compresion chamber set up like this.
-O
O O

Then i put my arm under it and use the pilot valve. Not very good looking though, which seems to be what I should be shooting for. I think....
Anyways, will a blowgun work as a pilot at 300 psi or should I use a ball valve?
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Unread postAuthor: mlz3000 » Tue Nov 23, 2010 10:21 pm

Yukondano2 wrote:Anyways, will a blowgun work as a pilot at 300 psi or should I use a ball valve?


I don't know about your blowgun, but I know the one I bought is only rated to 150PSI.

It seems that many prefer ball valves for their higher flow.
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Unread postAuthor: saefroch » Tue Nov 23, 2010 10:41 pm

Blowguns do have higher flow, but if you have a check-valved piston, the flow out your pilot (assuming you have a reasonably small pilot volume) doesn't really matter. If it's rated to 150psi, it's probably usable at 300, but I'd be very cautious.

You're thinking of putting three chambers together? If your C:B ratio is too high you might just be spending time watching the needle on that pressure gauge creep up for little benefit. Normally with metal builds one would use an over-under design (unless you're me) , with the chamber shorter than the barrel and under it. You'd then hold under the barrel with the left hand and hold the pilot valve with the right. Sight down the barrel.

Works pretty well if you can re-direct the pilot jet away from your clothes and don't mind something kicking so near your face.
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Unread postAuthor: mlz3000 » Tue Nov 23, 2010 10:48 pm

saefroch wrote:Blowguns do have higher flow


Wait, really?

This might have been a typo, but if you say so, I believe you (I'm still pretty new at this.)
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Unread postAuthor: jackssmirkingrevenge » Tue Nov 23, 2010 11:21 pm

mlz3000 wrote:This might have been a typo


I would hope so, when fully open even a 1/8" ball valve has much higher flow than a blowgun...
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Unread postAuthor: mlz3000 » Wed Nov 24, 2010 1:04 am

Alright, that's what I thought, thanks.

While we're kind of on the topic though, what's the biggest piston valve one could make where a blowgun would be sufficient as a pilot valve? Or would it just almost always better to use a ball valve?

Would a sprinkler valve modded with a blowgun perform appreciably better than one with a blowgun?
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Unread postAuthor: Lockednloaded » Wed Nov 24, 2010 1:15 am

IT depends on piston tolerances, JSR has piloted 3/4" valves with just a schrader, and the perform great if they don't EPIC FAIL

In my experience, a larger pilot valve is almost always better, but I don't build to tight specifications. And about the sprinkler valve; I've built both and I can tell you indefinitely the BV out performs
EDIT: ^ check the SV gun in my sig to see how I set it up
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Last edited by Lockednloaded on Wed Nov 24, 2010 1:31 pm, edited 2 times in total.
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Unread postAuthor: jackssmirkingrevenge » Wed Nov 24, 2010 1:16 am

mlz3000 wrote:While we're kind of on the topic though, what's the biggest piston valve one could make where a blowgun would be sufficient as a pilot valve? Or would it just almost always better to use a ball valve?


It depends on the efficiency of your piston valve. The example I always bring up in this case is this 1" piston for a 3/4" barrel which I piloted with a schrader.

With a tight piston and minimal pilot volume, you don't need a large pilot for good performance.

Would a sprinkler valve modded with a blowgun perform appreciably better than one with a blowgun?


No, a sprinkler valve modded with a blowgun should perform around the same as one with a blowgun ;)

Ball valves have greater flow when fully open, but if you're doing that manually the chamber will be empty before the valve is fully open, so unless the ball valve is quite large (>3/4") I doubt you would see the difference compared to a blowgun.
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Unread postAuthor: saefroch » Wed Nov 24, 2010 7:52 am

Some idiot wrote:Blowguns do have higher flow
*facepalmheaddesk* Yeah that was a typo.
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