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cup piston for a stirrup pump

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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cup piston for a stirrup pump

Unread postAuthor: CollegeGuy » Tue Apr 26, 2011 11:44 am

I was making a stirrup pump to finally ramp up pressure in my barrel sealing pneumatic till I realised that I had no access to O rings smaller than 1 1/2''
in diameter so I couldn't keep following the Gipetto's tutorial.
But then I thought about a cup pistons found in normal pumps and I started machining one on my poor man's drill press.
It's made from three superglued sheets of rubber making a 1 1/4'' high stack of rubber which now has got a cilindrical shape and needs a hole in the middle. My diameter of the pumps shaft is 16mm(not going to help non-europeans :P )
Was this this a good idea or not?
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Unread postAuthor: Crna Legija » Tue Apr 26, 2011 12:01 pm

i don't think super glue will last very long, you should get some rubber cement. you can get it from tire repair kit. aslo you could have just make your own size orng by cutting a oring and superglueing it back.
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Unread postAuthor: qwerty » Tue Apr 26, 2011 1:12 pm

The rubber will have to be cut perfectly to seal but other than that it should work.
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Unread postAuthor: CollegeGuy » Tue Apr 26, 2011 1:58 pm

Crna Legija wrote:i don't think super glue will last very long, you should get some rubber cement. you can get it from tire repair kit. aslo you could have just make your own size orng by cutting a oring and superglueing it back.



I'll see if it holds and if not then I'll try with rubber cement.


qwerty wrote:The rubber will have to be cut perfectly to seal but other than that it should work.



Well some smooth sandpaper can do a great job! :wink:
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Unread postAuthor: Technician1002 » Tue Apr 26, 2011 6:54 pm

Formed leather was popular with many pumps in the past. Leather is formed into shape when soaking wet. It is then fully dried which makes it somewhat hard. Then it is oil soaked which softens it while retaining the shape.

Many bicycle pumps used it as well as camping lanterns which ran on white gas.
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Unread postAuthor: CollegeGuy » Wed Apr 27, 2011 9:02 am

I've already heard about them. They look pretty good an easily made but I don't now were to get leather for this and as I already started work on the rubber cup I won't stop it.
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Unread postAuthor: mark.f » Wed Apr 27, 2011 9:49 am

Technician1002 wrote:Formed leather was popular with many pumps in the past. Leather is formed into shape when soaking wet. It is then fully dried which makes it somewhat hard. Then it is oil soaked which softens it while retaining the shape.

Many bicycle pumps used it as well as camping lanterns which ran on white gas.


I've hear different stories about how to make cup seals. Some people say use warm water to soften the leather to form it, and then let it dry, and some people say soak the leather in molten paraffin wax before pressing into the mold.

I bet both would work, and the paraffin wax one does have the advantage of marginal waterproofing (good in pneumatic pumps).

If your big chunk of rubber doesn't work, you can also make a rubber cup seal out of standard parts and a rubber washer (pictured below).

EDIT: Another thing you can do is this...

[youtube]http://www.youtube.com/watch?v=v36yZlFUQHU[/youtube]
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Unread postAuthor: CollegeGuy » Wed Apr 27, 2011 11:37 am

mark.f wrote:If your big chunk of rubber doesn't work, you can also make a rubber cup seal out of standard parts and a rubber washer (pictured below).


Dammit.... How didn't I thought about that? Never mind...I'll still try mine even though it looks a lot more work to get done than rubber cup seal even if I just have to make the inside of my the piston empty.

mark.f wrote:EDIT: Another thing you can do is this...


Well that is almost the same(or it is the same) as the rubber cup seal that you pictured.
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Unread postAuthor: mark.f » Wed Apr 27, 2011 11:40 am

Nope, that one is machined from a rubber tap washer (used in faucets) into the cup shape. Mines just a rubber washer (thin).
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Unread postAuthor: CollegeGuy » Wed Apr 27, 2011 11:47 am

mark.f wrote:Nope, that one is machined from a rubber tap washer (used in faucets) into the cup shape. Mines just a rubber washer (thin).


Then I don't get how does yours work. Sorry.
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Unread postAuthor: mark.f » Wed Apr 27, 2011 12:34 pm

It's just two sizes of washers. The top are the same OD as the ID of the piston track (with multiple to center the piston in the track of the pump), and the bottom washer is smaller than the ID of the track. A rubber washer larger than the ID of the track is sandwiched between them, and flexes.

The seal I linked to is made from a solid piece of rubber.
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Unread postAuthor: CollegeGuy » Wed Apr 27, 2011 1:29 pm

Yeah but nothing much is different from yours and the one in the video you just have those washers for centering and keeping the rubber washer in place on the pumps shaft. The rubber washer in your picture looks like a cup shaped one too.
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