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4 inch piston

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4 inch piston

Unread postAuthor: SP00K » Mon Jul 19, 2010 6:45 pm

What should I use for my 4" diameter piston?

Right now, I was thinking a 3" endcap with a mousepad for a sealing face, but I did just read a thread about epoxy casting one (although I have no experience there). Would 4 inches be viable for an epoxy piston, or is that too big?
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Unread postAuthor: clemsonguy1125 » Mon Jul 19, 2010 6:48 pm

Well that take a lot of epoxy unless you cast it around a pringles can or something, then filled the can with great stuff or something.
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Unread postAuthor: Lockednloaded » Mon Jul 19, 2010 6:51 pm

A 4" cast epoxy piston would destroy valve bodies; even if filled with foam you would need a substantial amount of epoxy and a sizable bumper. If I were you I'd use the 3" cap. The only issue with that though is that pressure rated caps are curved, but if you find a DWV cap, it should be flat
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Unread postAuthor: clemsonguy1125 » Mon Jul 19, 2010 6:59 pm

That would be heavy and crack or shatter easily, you would need a large heavy duty bumper for that.
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Unread postAuthor: Lockednloaded » Mon Jul 19, 2010 7:05 pm

he'll need a bumper for any piston this size, DWV is just as shatter prone as regular PVC so shattering should not be an issue with a bumper. Epoxy would be much heavier, and because it is so durable, it would not shatter itself, but instead the fittings which would be way more expensive than replacing a piston
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Unread postAuthor: jonnyboy » Mon Jul 19, 2010 7:09 pm

Yah a dwv cap would work well as for the bumper you could use half a nerf football or possibly a tennis ball.
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Unread postAuthor: clemsonguy1125 » Mon Jul 19, 2010 7:22 pm

I didnt mean it would shatter because it was DWV just that PVC shatters easily, Tech had a lot of issues with this on his Mouse Musket if I remember correctly, he will need a bumper with any piston, a PVC piston will just require a heavier duty piston.
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Unread postAuthor: SpudBlaster15 » Mon Jul 19, 2010 7:25 pm

Try to find a 3" DWV ABS cap; ABS is much tougher than PVC and will hold up far better in this application.
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Unread postAuthor: Technician1002 » Mon Jul 19, 2010 7:53 pm

The difficulty with the Mouse Musket was dealing with the hollow endcap. That does not provide a large flat surface for a decent bumper. My Dragon suffered the same problem. It too used an endcap. It used a 3 inch endcap (pressure rated domed) against a o ringed seat like the Mouse Musket. That cannon has a 6 inch PVC chamber, a 3 inch piston cylinder, with a 2.75 inch seat into a 2.5 inch PVC barrel. Getting a bumper that did not become chopped liver for dinner after a shot proved to be a problem. The edge chopped any bumper, which shattered the piston.

The QDV and the replacement piston for the Mouse Musket were both used to get away from hollow back pistons. They were too much trouble. A flat back works much better.

The piston in the ABS Cellular Core Cannon uses a flat PVC washer between the piston and bumper to take care of that problem. I am surprised the washer has not broken yet.

Cellular Core Cannon piston uses a washer to keep the bumper out of the piston recess. I think the only reason it has lasted so long is the low pressure it was used with most of the time.
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The washer was made with a hole saw. PVC pipe was heated and pressed flat first.
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Unread postAuthor: spudtyrrant » Mon Jul 19, 2010 8:06 pm

uhmw FTW, i have some extra 4" round stock that i could send you if you like, you would have to pay shipping of course. :wink:
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Unread postAuthor: Crna Legija » Tue Jul 20, 2010 1:06 am

the bore of a 351 is 4'' so its piston would fit :D
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Unread postAuthor: jackssmirkingrevenge » Tue Jul 20, 2010 1:25 am

Lockednloaded wrote:A 4" cast epoxy piston would destroy valve bodies; even if filled with foam you would need a substantial amount of epoxy and a sizable bumper.


With a bit of thought it can be made light and strong without using too much material. Some useful advice here.
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Unread postAuthor: SP00K » Tue Jul 20, 2010 9:49 am

Thanks Tyrrant, but the parts for this cannon cleaned me out for a while :P.

So if I sliced off the round top to my 3" endcap and put some flat pvc over both ends, could that suffice? I'm looking at 3 old mousepads I have, thinking 2 for the bottom as a bumper and 1 for a sealing face.

Right about now my gun is entirely finished except for the piston. Barrels are straight and edges are smooth and true. I'm using a sprinkler as my pilot valve.
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Unread postAuthor: Technician1002 » Tue Jul 20, 2010 10:00 am

I melted some ABS over the weekend. It may be possible to cast the stuff. That could be a fantastic piston. More testing is needed.
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Unread postAuthor: clemsonguy1125 » Tue Jul 20, 2010 10:18 am

Whats the tempature needed to liquify ABS, how long does it stay liquid, I can see it being used for pistons, vortex blocks, ammo, and asthetics.
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