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"In the world of spuds today"

A place to ask general spud cannon related questions.
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Unread postAuthor: saefroch » Sun Apr 10, 2011 3:00 pm

Fnord wrote:I don't know how much more clearly I can state it without a picture.
Sorry... I guess I do require a picture then.

My internal piston is not stepped, it looks much like that in your original drawing. The piston simply pushes forward, so that it when it hits the barrel fitting, the main piston moves backwards and cracks open.

My piston is going to slam into my spring... but I don't think I'll have an issue with bottoming out, since the spring is closed and ground on both ends, and its OD is the ID of the spaces, and the ID of the spring should the the OD of the internal piston... sadly not leaving any room for a spacer without compromising the integrity of the valve components.
Oh wait... if it slams forward into the barrel fitting or whatever before full compression of the spring, doesn't that prevent "slamming" to some degree?
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Unread postAuthor: Fnord » Sun Apr 10, 2011 3:10 pm

if it slams forward into the barrel fitting or whatever before full compression of the spring, doesn't that prevent "slamming" to some degree

Yes! That's good.

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Unread postAuthor: saefroch » Sun Apr 10, 2011 3:28 pm

Couldn't that force the piston back shut after firing? I mean I know the loss will probably be minimal, but it'd probably overcome the advantage of using a QDV in the first place...
We were thinking of the valve in different orientations. I suggest terms like "chamber side" "pilot side" and "barrel side" in the future. To me "below" indicated "chambers side" or some yet unnamed doohickey off to the side.

Any ideas on an effective bumper that won't mutilate my piston (I'm leaving about 4", or 2 lengths of piston available behind the valve but I may decide to extend that), keeping in mind that at the bottom of the o-ring grooves I only have about 0.086in<sup>2</sup> of steel? :?
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Unread postAuthor: Fnord » Sun Apr 10, 2011 3:32 pm

Ok, I can see where we're having a communications breakdown here.
Take a bit of time to draw a diagram of your design so I can be sure I'm not misunderstanding anything.

Also, yes, the valve may shut completely after the shot, but this will depend on the spring pressure. However you may still end up pulling a vaccum in the chamber since the little gas remaining will cool off rapidly.
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Unread postAuthor: saefroch » Sun Apr 10, 2011 3:45 pm

Obviously crude, but it should give the general idea:
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Unread postAuthor: saefroch » Tue Apr 12, 2011 2:08 pm

ITWOST:
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Unread postAuthor: mark.f » Tue Apr 12, 2011 4:17 pm

Huh. Did you get around to casting the epoxy yet?
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Unread postAuthor: saefroch » Tue Apr 12, 2011 4:25 pm

Nope. That'll be tonight or tomorrow, I can't locate my drill somehow, and I'm not cleaning the little lips off those nipples by hand. I'll probably start a new thread when I start casting the epoxy. A little bit I did anyway:
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Unread postAuthor: jackssmirkingrevenge » Sat Apr 16, 2011 4:04 am

I smell an HPA semi-auto...
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Unread postAuthor: al-xg » Sat Apr 16, 2011 8:12 am

You might need to re-drill the exhaust port, much more like a bleed port really...

Or maybe if you have a small drill bit, drill more holes, a larger hole 2-3mm dia, will eat away the O-ring. although a replacement for that particular one can be found in plumbing shops.

Oh and yeah, the recorded lack of flow was on a 3/4 QEV, with minimal pilot volume. Re-drilling made a big difference to power.
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Unread postAuthor: jackssmirkingrevenge » Sat Apr 16, 2011 8:33 am

Sound advice, though I figure it's about the same flow as a schrader so should serve me well as is, the plan is to have it in conjunction with a detent too.
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Unread postAuthor: al-xg » Sat Apr 16, 2011 10:16 am

Mine only had a single 1mm hole, its quite easy to check if you remove the end O-ring.
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Unread postAuthor: Labtecpower » Sat Apr 16, 2011 10:49 am

the piston setup sb15 and mrc use looks like this. Am I right?

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Unread postAuthor: Gun Freak » Sat Apr 16, 2011 10:51 am

Thats pretty much what it looks like except you need a spot for a fill valve behind the piston.
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Unread postAuthor: jackssmirkingrevenge » Sat Apr 16, 2011 10:59 am

al-xg wrote:Mine only had a single 1mm hole, its quite easy to check if you remove the end O-ring.


Mine has a single 1.5mm hole.

A schrader has a 2mm hole with a 1mm stem through it.

0.01767 cm<sup>2</sup> cross section vs 0.02357 cm<sup>2</sup>, so not as "good" as a schrader, hmm...
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