pilot vent to close a blow forward bolt

Show us your pneumatic spud gun! Discuss pneumatic (compressed gas) powered potato guns and related accessories. Valve types, actuation, pipe, materials, fittings, compressors, safety, gas choices, and more.
iknowmy3tables
Staff Sergeant
Staff Sergeant
Posts: 1571
Joined: Fri Dec 15, 2006 3:57 pm
Location: maryland

Tue Mar 09, 2010 7:06 am

so polandspud showed me this animation in another thread awhile back
Image
read carefully what I'm suggesting isn't the same as this animation
so in this system the piston that pushes the bolt forward can't be air tight and the restriction it creates on the pilot reduces power slightly, however I was thinking, for a regular blow-forward bolt attached to a 3way and qev, what if you connected the pilot exhaust to the front of the piston, perhaps the the pilot air might help close the blow-forward bolt either fully or partially before the qev opened so the main blast of air would encounter less resistance from the blow-forward bolt when it finally opens.
would the restriction on the pilot flow make this less powerful or would the reduced resistance for the air from the qev make this more powerful then the regular blow-forward setup
Last edited by iknowmy3tables on Wed Mar 10, 2010 11:31 am, edited 2 times in total.
User avatar
POLAND_SPUD
Captain
Captain
Posts: 5402
Joined: Sat Oct 13, 2007 4:43 pm
Been thanked: 1 time

Tue Mar 09, 2010 3:18 pm

yeah that's a cool design and cool animation.. I had to look at it for 20 minutes or so to work out how it works :D
perhaps the the pilot air might help close the blow-forward bolt either fully or partially before the qev opened so the main blast of air would encounter less resistance from the blow-forward bolt when it finally opens
the problem is that the performance will be reduced if piloted air can't be vented freely... sure you can use a chamber to provide more volume for it to expand, or a larger pilot valve/small qev to assist piloting...

though, I think that it's more complicated than just the QEV + 3 way valve + air cylinder combo, which offers zero restrictions in the first place...

lol I guess I am being repetitive... I wrote at least 3 or 4 similar sentences today :D
Children are the future

unless we stop them now
User avatar
Patto
Private 4
Private 4
Posts: 96
Joined: Wed Jan 20, 2010 7:08 pm

Tue Mar 09, 2010 4:23 pm

He he he echo, echo .... :lol:
iknowmy3tables
Staff Sergeant
Staff Sergeant
Posts: 1571
Joined: Fri Dec 15, 2006 3:57 pm
Location: maryland

Tue Mar 09, 2010 7:36 pm

yeah but in this case what I'm just thinking of is not exactly what's in the animation, it just uses the concept

what I'm suggesting is just a conventional blowforward bolt with the pilot exhaust redirected to behind the bolt instead of the atmosphere,

I've already stated that the restriction of the pilot is a negative factor towards performance, however the reduced restriction on the qev output could make up for this
User avatar
BigGrib
Corporal 2
Corporal 2
Posts: 652
Joined: Mon Oct 01, 2007 11:43 pm
Location: TriCities, WA
Contact:

Tue Mar 09, 2010 7:47 pm

ok here's my take on it, the line going to the bolt from the res in the back remove that and put it to the res by the piston, that way when you fill the chamber it'll blow the bolt forward, put a spring in there to slide the bolt back after discharge that way air pressure overcomes spring pressure to close the bolt and then dumping the pilot opens the piston and the spring jacks the bolt back.
Yea, that's definitely going to get you at least a tazer.
<a href="">DONT TAZE ME BRO.. DONT TAZE ME... AHHHH</a>
facebook.com/biggrib
User avatar
POLAND_SPUD
Captain
Captain
Posts: 5402
Joined: Sat Oct 13, 2007 4:43 pm
Been thanked: 1 time

Wed Mar 10, 2010 2:54 am

perhaps the pilot air might help close the blow-forward bolt either fully or partially before the qev opened
hmm I've just noticed something... just to make sure I get your idea... you want to vent the volume between the QEV and the blowforward bolt, right ?? well there is one possible problem here

QEVs stay shut because of pressure differential pushing the piston/poppet against the sealing face... but then you direct air from the pilot side to the volume between the QEV and the blow forward bolt the pressure is almost the same on both sides of the piston/QEV... I wonder what would happen then and when the QEV open?


will it stay closed ? I don't know

will the QEV fire prematurely :D (before the BFB loads ammo) ? IDK

will the piston bounce back as soon as the QEV opens (since air can pass from the barrel side of the QEV to the pilot side of it... sure you can put a check valve there but that makes it more complicated)? IDK

what effect will it have on performance? IDK

anyway, it seems that the expected advantage of this design....
the main blast of air would encounter less resistance from the blow-forward bolt
might not be worth it at all
Children are the future

unless we stop them now
iknowmy3tables
Staff Sergeant
Staff Sergeant
Posts: 1571
Joined: Fri Dec 15, 2006 3:57 pm
Location: maryland

Wed Mar 10, 2010 7:28 am

@poland spud: I think you got it
the qev wouldn't stay closed, note that plenty of diaphragm valves that don't hold plain compressed air vent pilot volumes towards their outputs

but the rest of the uncertainties you mentioned, I'm pretty uncertain about this, which is why I posted this, cause I don't know

if it is true then anyone attempting a semiauto blowforward qev gun could make an easy adjustment to improve their gun
User avatar
psycix
Sergeant Major 4
Sergeant Major 4
Posts: 3684
Joined: Mon Jun 25, 2007 7:12 am
Location: The Netherlands

Donating Members

Wed Mar 10, 2010 7:38 am

I like this system. But it indeed has some possible issues.
I'd drill a vent hole in the side so that the blue part can move forward without compressing air.

It might need a checkvalve in the small line leading to the bolt to prevent the mentioned leak into the pilot of the red part, closing it.



The main advantage of this design is the simplicity. Especially the simplicity in manufacturing.
Till the day I'm dieing, I'll keep them spuddies flying, 'cause I can!

Spudfiles steam group, join!
Post Reply