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Blowgun or solenoid pilot

Unread postPosted: Fri Jan 14, 2011 1:22 am
Author: cfb_rolley
I'm thinking of trying my hand at building a pneumatic cannon again, my last one was a 30mm diameter port T piston, which worked but eventually the piston got stuck. This time I want to build a smaller one, probably a 17ish mm port 30mm piston coaxial piloted by a blowgun. However I'm not sure if the blowgun will dump the pilot well enough to get average performance. Pilot will be 30mm diameter x 10mm or hopefully shorter.

The other option I could do is try slightly bigger and use a solenoid valve as a pilot, that way I could make an electronic trigger setup, but I know very little about solenoid valves.

Any hints/tips/better input?

Unread postPosted: Fri Jan 14, 2011 5:04 am
Author: Crna Legija
if you make a tight piston and use a modded blow gun it will be plenty

Unread postPosted: Fri Jan 14, 2011 5:11 am
Author: cfb_rolley
Sweet. The piston will have o-rings and I'll glue rubber bike tube on the sealing face, but drill a hole through beforehand and leave a small section free of glue so that the rubber acts as a check valve

Unread postPosted: Sat Jan 15, 2011 4:50 am
Author: cfb_rolley
First off sorry about the double post, phone won't let me edit properly for some reason, and I didn't want to start another thread either..

Decided I'll go with a 1/2" solenoid valve, they seem simpler than I first thought. But, would I need a separate fill port or could I fill through the outlet of the solenoid valve? Also if it were a 12v dc one should I try feeding it a higher voltage to make it open faster or would it work just fine anyway?

Unread postPosted: Sat Jan 15, 2011 5:49 am
Author: POLAND_SPUD
it depends what you understand by the term 'solenoid valve'

Is it a direct acting or indirect acting valve ?

If you have no idea what I am talking about it might be a good idea to read this >>
http://www.spudfiles.com/forums/directi ... 20438.html

I admit that these things does seem a bit complicated and overwhelming at first but once you understand the basics you will realise that it isn't all that complicated


Personally I think you'd be better off with a blowgun or a manual 3 way valve (even a 3/8" slide valve should work great) but that's just my opinion

ohh here is a slide valve
Image

Unread postPosted: Sat Jan 15, 2011 6:59 am
Author: cfb_rolley
well i was thinking either this:
http://cgi.ebay.com/1-2-Nylon-Solenoid-Valve-NPSM-Thread-Control-Water-12V-/110500871216?pt=LH_DefaultDomain_0&hash=item19ba5d7c30#ht_571wt_1135

or the 3/4" version of it. as far as i can tell it's indirect? could be wrong though. reason being if i decided to go a bit larger I don't think the blowgun would be enough. And another project on my mind is using one for a setup inside a nerf gun simply to flow air, not to actuate anything with a button behind the existing trigger and a battery pack in the stock to operate it.

Unread postPosted: Sat Jan 15, 2011 7:07 am
Author: POLAND_SPUD
I am not sure how well it would work with air - should be OK but you never know. Also it is made of plastic, rated to just 120 psi and has some unusual threads

I am pretty sure you can find some heavy duty 3 way valves on ebay for that much

Unread postPosted: Sat Jan 15, 2011 7:55 am
Author: cfb_rolley
so this or a manual version would perform much better as opposed to the diaphram one above right? how big of a piston could i pilot with this?

http://cgi.ebay.com/3-Way-2-Position-Solenoid-Air-Valve-1-2-NPT-12V-DC-/250503492095?pt=Pneumatic_Hydraulic_Valves_Parts&hash=item3a532bf1ff#ht_2774wt_1083

sorry, i'm not too switched on when it comes to pneumatics, a fair bit more to it than combustion cannons. just want to make sure i get everything right.

Unread postPosted: Sat Jan 15, 2011 8:20 am
Author: POLAND_SPUD
a 1/8" valve can pilot a 1/2" QEV without any problems...
1/4" valves (and some 1/8" ones) are adequate for 3/4" QEVs...

so my guesstimate is that a 1/2" valve should be able to pilot a 1" piston valve or maybe slightly larger

Opening time has big influence not only on the main valve (and thus the performance of the gun) but also on piloting of the main valve. Solenoid valves do have an advantage as they open faster than, let say a ball valve, blowgun or a direct acting manual 3 way valve...

So... while a 1/2" 3 way valve doesn't have as good flow as a 1/2" ball valve it in fact is a better pilot than the latter as it opens completely faster (not to mention that it is a lot more consistent which has an effect accuracy)

Unread postPosted: Sat Jan 15, 2011 7:44 pm
Author: cfb_rolley
cool. so using a solenoid would also take away the human error that happens with opening a manual valve. also, you could have a safety switch wired in series with the trigger button to prevent accidental firing. sounds like a fairly attractive type of setup..

just for the sake of theory, would hooking up 2 seperate 1/2" solenoid 3 way valves to the one button to open them both to dump a single pilot work for bigger pistons?

Unread postPosted: Sat Jan 15, 2011 11:01 pm
Author: POLAND_SPUD
just for the sake of theory, would hooking up 2 separate 1/2" solenoid 3 way valves to the one button to open them both to dump a single pilot work for bigger pistons?
Generally speaking if you want to reduce piloting time you use a quick exhaust valve - that's what they are used for in real life

If you compare flow of a typical 3 way valve of a given size with a qev of the same size you'll notice that the QEV has several times higher flow. Find a datasheet on QEVs and compare that with flow of any DCV.

EDIT (found them for you)
http://catalogue.camozzi.com/res/pdf/ENG_2_2_10.PDF
http://catalogue.camozzi.com/res/pdf/ENG_2_6_05.PDF

You could use a smallish 1/8" valve that pilots a 3/8" QEV that in turn pilots your main valve - that's 100% doable and generally speaking is cheaper than getting a larger valve
(This works great... though you might encounter a problem if you want to build a fullauto gun that fires, let say 5 rounds per second, as the valve might not have enough flow to alternatively fill and pilot the system 5 times a second)

Now to answer you question directly.... since flow increases exponentially as you increase the size of ports, you would get better flow with one larger valve than two smaller ones (two 1/2" valves have lower flow than one 3/4" - Twice the diameter equals four times the flow). So if you need more flow it is cheaper and more practical to just buy a larger valve.