Airgun for developing countries

[Gippeto]

Have found the program to be fairly accurate providing it's fed accurate information and the predicted velocities are below 900fps...above 900fps it's  just not accurate at all.

1" npt and smaller fittings are available to you? Can you get hydraulic fittings? They're usually machined inside as opposed to the cast varieties.

Checked a 1" coupling I had on hand, it's just over 2" in length, some quick and rough calculation shows it having roughly .9 cuin  once assembled.

Al

[nikp]

Couldn't help myself.
Chamber is made from 30 mm steel.  Spool also steel but drilled out to lighten.  No Oring as yet.  Feed to reservoir and from pump both NPT compression fitting elbows.  Barrel in place is only for test purposes.  Hopefully I get to test it tomorrow

[rsterne]

It looks like there is a lot of volume to the right of the spool.... That air must be dumped to shift the spool and create the shot.... The larger the volume, the slower the air will dump out through the blowgun nozzle when you pull the "trigger".... The slow dump of air won't slide the spool very quickly, and opening it slower will reduce the velocity of the shot.... Also, the small inlet below the spool won't help either....

It should fire, just not perform well, IMO....

Bob

[nikp]

You're right. Working on the fix.
Gippeto, the semi circle hole you drill into the oring groove - it's obviously only as deep as the groove but does it matter where on the circumference it is? Your spool would rotate placing the hole opposite to the reservoir outlet I assume. I'm guessing it's irrelevant where it is as the air is moving around the spool and into the reservoir. Probably over thinking this

[Gippeto]

You got 'er..any where around the circumference is fine.

If you drill out the spool, that volume becomes part of the pilot volume. What some folks have done is fill it with something light but bulky and then cap it with epoxy...JB Weld/Araldite.

Pilot volume can be a killer, and it can be hard to get rid of while maintaining a .2" (~5mm) diameter passage you need for air to vent off.

Other thing some folks have trouble with is the fit of the spool to its bore...needs to be a very good fit...almost snug. The use of the o-ring will take care of that.

Your final build should not make use of that plastic tubing to feed the valve...it will hurt performance.

Al

[nikp]

Al,
Did you ever do any work on fitting your hand pump to an airgun?  I'm looking at modifying your design to make it an integral part.
The lever action and the fulcrum affects are of interest.
Nick

[Gippeto]

No, I never tried to fit in on. Quite a few folks around that have built pumpers based on the Crosman rifles...maybe one of them could chime in with some dimensions as a starting point on the geometry??

Al