Adjustable piston

[alkalineall]

Here is an idea for everyone that I implemented in my latest cannon. You know those test plugs that they sell to compression seal one end of pvc pipe? (theyre made of metal and have an adjuster wing nut). Well I took two of them and trimmed the larger metal ring that keeps it from entering the pvc off on both units. Then I removed one of the carriage bolts and threaded it through the both of them with some washers in between as a spacer. I glued a nice thick gasket on to the end for my barrel seal and adjusted the tension on the bolt to expand it to correct fit. Works great and no lathing/sanding etc to fit. If anyone has done this before I apologize for being un-original If not hope this helps. I know a picture is worth a thousand words but I'm tired and up too late already. Maybe tomorrow if anyone wants to see.

[MrCrowley]

yeah i would like to see a picture

[alkalineall]

Ok hope that helps. Let me know what you think. To adjust the fit you just tighten the nut on the end. That expands the two rubber rings. Works for me and there is no trimming/ sanding or other irritating crap.

[pyromanic13]

awesome idea!

[mark.f]

What are these called? The name they use at hardware stores?

EDIT: and now for more questions...

What sizes do these things range through?

Are they sized on what size pipe they seal off, (YES, I know they're adjustable, but you still won't get a pipe range so large they only sell one!)?

Can you get a perfectly airtight seal using one of these, (I would imagine so, since they're designed to seal pipe)?

What material are they? If lubricated, would it be able to maintain a seal in the pipe yet still slide back and forth in a piston carriage? Would the material be damaged by petroleum based lubricants? (I use petroleum jelly or gun oil usually to lubricate pistons)

Not to sound annoying, and I could probably answer all these questions at the hardware store. Thing is, I don't have another day off where I can get there until next Monday!

[alkalineall]

Markfh11q: They call them "test plugs" at the hardware store. They're pretty common. I have personally seen 2" to 4" and there could be more but thats all that I can attest to having seen on the shelf myself. Yes, they say what size pipe they are for on the top of the plug. You may have to adjust back and forth a little to get the best seal/movement. Mine seal pretty well and still slide easily, but I think that some kind of lube would be a good idea. The only reason that I haven't is bc I'm not sure what kinds of lube eat which kinds of rubber or plastics. I'm not sure what they are made of but it seems like the rubber parts are the same type as most black gaskets for drains and such. Maybe buna-n?. I'm sorry I don't know too much about this area of things. And don't worry about the questions thats what this place should be about right? Oh and the metal parts are some kind of low grade steel I think(they cut pretty easily with a hacksaw/dremel).

[MrCrowley]

What about these for a chamber sealing piston:

I saw them at a boat shop yesterday, theyre used for trailers to roll boats along them and theyre made of rubber,
really strong and sturdy,might seal good and all ready have an eq hole drilled through the middle

edit:And you can get them from about 3/4" all the way up to 3" or 4" size for $20NZD($12US). Here's a website with some more:
http://www.boatbits.co.nz/shop/Chandler ... llers.html

[mark.f]

Okay then, thanks alkalineall! I'm just gonna look up "test plugs" on McMaster.

Ha ha... I've found them! The metal is cast iron and the seal is natural rubber.

The would be very useful indeed. 8) Great find.

[alkalineall]

Cool, glad I could help. Unless you need other items from McMaster, they have this item at almost all plumbing retailers. I got mine at Lowe's and almost every place has them. It would just save you shipping if thats all that you need.
MrCrowley: Could work. And they are soft and pliable I'm guessing? which would be less threatening to the pvc when it snaps open. I think I recognize where those go.

[Infernal2]

Allkalineall, I've been trying to use these as well. You seem to have come up with a better system than I have. Congrats, and thanks.

A side note, if you can find repair buttons for elevators (I know, pretty rare) then they work great as a spring that attached directly to the piston.

[noname]

Crowley, that thing looks like 2 ABS bell reducers taped together.
And alkalineall, great find!

[alkalineall]

Thanks guys. I've been eyeing these things for a while and I knew what I wanted to do with them but it just took me a little while to figure out exactly how. Hope I helped .

[MrCrowley]

Crowley, that thing looks like 2 ABS bell reducers taped together.
And alkalineall, great find!

yeah lol i dont know what the tape is for but theyre as strong as a brick a little heavy too but you can cut them down or use them on a massive gun.

[pyrogeek]

Why do people use petroleum lubricants? If you are concerned about ruining the rubber, just use a lubricant like vegetable oil. They also sell silicone lubricants for air guns and paintball guns. Heck, that's what a lot of good personal lubricants are.

How about this, someone give me one good reason to use petroleum.

[noname]

It's cheap and most people already have some around.