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Sticky 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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Unread postAuthor: brogdenlaxmiddie » Sat May 17, 2008 9:27 am

jrrdw wrote:
Due to my slow typing brogdenlaxmiddle had edited and reposted the correction I did not see that not seeing the edit, lead me to post the above mentioned, that now makes no sense....... :oops: sorry.


Hey, I was talking about putting it on the sealing face. The way he described it was him saying that he put it on the sides, not the sealing face. So, Before you think im a total dumbass, re-read what you told me to read...

No, your not, not at all, jrrdw.
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Unread postAuthor: Gippeto » Sat May 17, 2008 9:54 am

I would have figured you could pilot (just about) anything with a 1" sprinkler. :shock:

If improving the "fit" doesn't work, measure up (od.'s of) your piston and valve seat, the problem might be there.
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Unread postAuthor: psycix » Sat May 17, 2008 3:59 pm

My recommendation:
Pull of the duct tape and put new on again.
Put so much on it that it hardly fits in again.


Wait, i just re-rode the thread and maybe the difference between the porting and the piston diameter is too small?
Piston is 2"?
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Unread postAuthor: daberno123 » Sat May 17, 2008 4:25 pm

Looking at this picture you will notice that there is hardly any area on the front side of the piston when it is pressed against a piece of 1.5" pipe.

Image

So now that we've located the problem, anyone have any possible fixes for it?
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Unread postAuthor: jrrdw » Sat May 17, 2008 4:58 pm

Line the barrel so that the smaller lining protrudes a 1/4" further into you valve. You will have to make sure that the sealing face still will seal against the smaller pipe. Thats my idea.
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Unread postAuthor: daberno123 » Sat May 17, 2008 5:06 pm

Good idea jrrdw but I would rather try something that doesn't involve remaking the porting, but instead something with the piston. Is there any way I could add area to the piston so I don't have to make the porting smaller?
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Unread postAuthor: jrrdw » Sat May 17, 2008 5:22 pm

Bigger backing washer, but can you fit it into the tee?
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Unread postAuthor: daberno123 » Sat May 17, 2008 5:34 pm

Actually, there is no backing washer, just the 1.25" cap.

If I were to make a new piston using neoprene sheet as a sealing face, I could cut it out a little bigger than the ID of the 2" pipe so there would be a little more area around the 1.5" pipe when sealed. The sealing face could just be epoxied on to the end of the cap.

Do you think it would work then?
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Unread postAuthor: brogdenlaxmiddie » Sat May 17, 2008 8:03 pm

jrrdw wrote:Bigger backing washer, but can you fit it into the tee?


That's what I would do, otherwise it just pushes the sealing parts into the barrel and fits it really snugly into the barrel. So, like jrrdw, put in a backing washer
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Unread postAuthor: jrrdw » Sat May 17, 2008 8:15 pm

A washer behind the seal would help. If you make it bigger then the piston it would give you the surface area your looking if you can fit it into the tee.

The problem with this idea is the piston will no longer slide all the way back into the cylinder it slides in. It will probly hammer your valve to pieces.

I think lining the barrel is really your best bet, it wont cut down the port size to badly.
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Unread postAuthor: watto » Sat May 17, 2008 9:32 pm

Ok, to me that piston looks very heavy, the tape looks far too rough and would let too much air through and is there a reason you have that massive heavy nut? Wouldn't that restrict the flow?

So If I was you Ide get rid of the cloth tape and huge nut then get some smooth, thick electrical type tape and wrap it till its tight enough in the housing so it doesn't wobble but loose enough so you can push it back and forwards with your breath. Take your time wrapping the tape and make it perfectly smooth.
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Unread postAuthor: psycix » Sun May 18, 2008 6:50 am

Ahh I see!
You are trying to seal a 1,5" porting with an 1,5" piston?
That means youve got NO frontal area for the pressure to work out force on.

You need to make this area.
This can be done in one of these ways:
-Smaller porting (but restricts flow)
-Larger piston (and thus a larger piston housing)

You will HAVE TO do one of those things if you want to make it work.
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Unread postAuthor: SpudFarm » Sun May 18, 2008 6:59 am

mabe you can use some springs that pulls the piston back like 1/100" and then the pressure can work on the whole sealing face
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Unread postAuthor: psycix » Sun May 18, 2008 7:28 am

@ spudfarm
That COULD work, but would be innefficient....
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Unread postAuthor: SpudFarm » Sun May 18, 2008 7:47 am

but it is waay better than build the whole housing one more time
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