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Balanced UnBalanced Piston

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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Re: Balanced UnBalanced Piston

Unread postAuthor: jackssmirkingrevenge » Wed Aug 16, 2017 4:36 am

Gippeto wrote:Any chance of finding the right size tube to use between the o-rings? Short sections of tube sanded square using the drill press


This is another way of doing it, the APS airsoft shotgun cartridge does this in a similar way:

Image
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Re: Balanced UnBalanced Piston

Unread postAuthor: airatomic » Fri Aug 18, 2017 4:08 am

JSR, thats a cool option. Can you draw up a quick diagram on the internal working of the CAM 870?

MrFoo, thank you for the long long explaination. I wished to have more complete tools to do all that. But the tools I have are basics, and a lot of the fabrications I did were just out of the box. Very ghetto or macgyver style, so to speak.

Here are some options:

1)
3way_slide2.jpg

Place matching metal washers (in yellow) around the o-rings, before casting in fiberglass resin once again. That should give "cleaner" edges when its cure.


2)
3way_slide3.jpg
3way_slide3.jpg (9.78 KiB) Viewed 275 times

Cut out matching spacers (in red) from metal or nylon blocks, epoxy them between the o-rings. This provides even "cleaner" edges. Only concern is how strong the epoxied spacers will be, as the pressure (psi) increases. If I do this, I will drill in some screws to the body of the spacers from outside to make it more solid and safe.



While pondering the above, I played around with the following:

DSC_2485.JPG


and

DSC_2482.JPG


for

DSC_2466.JPG

Attempting to make a 3-way ball valve. Similar to the slide valve's objective.


Thats before I went to check the internals of a ball valve, and assumed that the teflon shield covered the entire internal. When it was not so; only around the ball valve's 2 exits. The tiny screw epoxied to the body was to shield the hole I made earlier to fix the problems, but the hole through the shiny ball cannot be fixed already, obviously.

Still, it was a good experience. ;)
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Re: Balanced UnBalanced Piston

Unread postAuthor: jackssmirkingrevenge » Sat Aug 19, 2017 9:30 am

airatomic wrote:JSR, thats a cool option. Can you draw up a quick diagram on the internal working of the CAM 870?


The CAM 870 operating mechanism is virtually identical to your typical pump action firearm (click image for non-medieval gifv):

Image

The cartridge is a simple balanced spool that is knocked open by a hammer striking a firing pin, here are some more detailed images of the internals:

Image

Image

Image

Image

The small hole in the spool is for filling purposes, when fired the gas flows around the grooved portion.

Place matching metal washers (in yellow) around the o-rings, before casting in fiberglass resin once again. That should give "cleaner" edges when its cure.


I don't think the washers are needed, this is an unnecessary complication. O-rings used directly should work just as well provided that they are not slack on the mandrel when casting.
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Re: Balanced UnBalanced Piston

Unread postAuthor: airatomic » Mon Aug 21, 2017 8:35 am

Thanks for photos effort, JSR.

I keep wondering how the intermal of the spool looks like. Both ends of the spool got hole, and it seems to be a tunnel from one end to the other. There is a hole on the body at the end of one side. In which case, how can it be a balanced spool? How does it work when infilling it with compressed air, and storing it in this manner?

Having a diagram of the spool's internal will making things clearer, i think.
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Re: Balanced UnBalanced Piston

Unread postAuthor: jackssmirkingrevenge » Mon Aug 21, 2017 7:41 pm

Here's a diagram, should be clearer now. The cavity in the rear of the spool is not open to the chamber, it just anchors the spool in the fill rig while pressurizing.

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Re: Balanced UnBalanced Piston

Unread postAuthor: airatomic » Mon Aug 21, 2017 9:21 pm

Thats much clearer. Thanks for diagram, JSR. That's quick. The legend lives on.

Now this is a clever alternative to my previous one. I like the part where you can service the internals. Lets see if i can fabricate something similar. Without the mess of casting.

Turning this into a slide trigger requires some thoughts. The incoming air from the chamber is from one end. Piloting it goes the opposite end. Hmm..
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