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stirrup pump help

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Unread postAuthor: MrCrowley » Fri Feb 06, 2009 5:50 pm

Read this:
http://www.spudfiles.com/forums/easy-st ... 13277.html

The horrizontal handle is attached to a verticle pipe/tube/rod on one end, and on the other end of this pipe/tube/rod is the piston.

This piston goes inside a piece of pipe which is the 'compression chamber' more or less. This is where the piston compresses the air when you push the pump down. At the bottom of this chamber is a check valve, this stops air going back into the compression chamber.

That's a brief description, read the topic I linked. It should help.
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Unread postAuthor: Hubb » Fri Feb 06, 2009 5:50 pm

And the check valve only allows flow towards the bottom of the pump. It opens on the upstroke, then closes on the downstroke.

It seems to me you got it. Have more confidence.
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Unread postAuthor: MrCrowley » Fri Feb 06, 2009 5:52 pm

hubb017 wrote:And the check valve only allows flow towards the bottom of the pump. It opens on the upstroke, then closes on the downstroke.

It seems to me you got it. Have more confidence.

It seems i've joined in halfway through this conversation, to clarify about the check valve...are you talking about a floating o-ring on the piston, or the check valve at the bottom of the pump?
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Unread postAuthor: daniel323 » Fri Feb 06, 2009 5:53 pm

ok i will :lol:
but can these check valves be store bought

and if they are will you still need to make a piston

thanks
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Unread postAuthor: MrCrowley » Fri Feb 06, 2009 5:57 pm

but can these check valves be store bought

and if they are will you still need to make a piston

Okay I think you are a little confused.

I have a feeling hubb017 is talking about a check valve on the piston. This is generally a floating o-ring. When the piston is pushed down, the floating o-ring seals against the chamber walls to stop air going past it. When the piston is pulled up, the o-ring doesn't seal against the chamber wall and allows air to flow back into the chamber so you can compress it on the down stroke.

A floating o-ring acts like a check valve more or less but cannont be store bought for this application. Read this page on floating o-rings:
http://www.rlhudson.com/O-Ring%20Book/d ... namic.html

Figure 115 shows a diagram of one and read this paragraph to help understand it:
In floating O-ring designs, however, there is no radial squeeze on the seal’s cross-section. The O-ring’s O.D. is larger than the cylinder bore diameter. Peripheral squeeze is applied to the O.D. as the O-ring is installed into the bore. Incoming air pressure forces the O-ring against the groove wall, and a seal is effected as shown in Figure 115.


There is also usually a proper check valve at the bottom of the pump, this allows the compressed air to travel into your cannon, but stops it from coming back into the pump. If your check valve fails, all the compressed air will flow back into the pump's chamber, and force the piston up. This happened to one of your members and he got hurt quite bad. Mind you that was at around 1000PSI.

These check valves can be store bought.
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Last edited by MrCrowley on Fri Feb 06, 2009 5:59 pm, edited 1 time in total.
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Unread postAuthor: Hubb » Fri Feb 06, 2009 5:58 pm

Whether you purchase or build a check valve, it will need to make a seal inside the pump (which is what the piston is for).

Above, MrC referred to a floating o-ring. These provide a seal and a check valve at the same time.

Edit: We seem to be posting at the same time, there, MrC. :lol:
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Last edited by Hubb on Fri Feb 06, 2009 5:59 pm, edited 1 time in total.
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Unread postAuthor: maggotman » Fri Feb 06, 2009 5:58 pm

some use a tee at the bottom with 2 check valves one in and one out but they have a disadvantage of having more dead space.
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Unread postAuthor: MrCrowley » Fri Feb 06, 2009 6:01 pm

hubb017 wrote:Edit: We seem to be posting at the same time, there, MrC. :lol:

We sure do, probably confusing him a bit with our different explanations. But have no fear, i'm going out soon and i'll leave all the posting to you :wink:
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Unread postAuthor: daniel323 » Fri Feb 06, 2009 6:04 pm

so MrCrowley can you buy a floating o-ring piston ?

or should i go off gippetos piston
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Unread postAuthor: Hubb » Fri Feb 06, 2009 6:07 pm

I've never seen one you could purchase. Besides, if you could, it'd probably be cheaper to build one anyway.
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Unread postAuthor: MrCrowley » Fri Feb 06, 2009 6:11 pm

daniel323 wrote:so MrCrowley can you buy a floating o-ring piston ?

or should i go off gippetos piston

MrCrowley wrote:A floating o-ring acts like a check valve more or less but cannont be store bought for this application

:)
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Unread postAuthor: daniel323 » Fri Feb 06, 2009 6:11 pm

ok so i think i get it, there is a handle that is attatched to a small tube, that is attatched to a piston (i will go off gippetos piston probably because thats the only way i know how) and then there will be a check valve that the air gos through and cant come back through?
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Unread postAuthor: LikimysCrotchus5 » Fri Feb 06, 2009 7:43 pm

Also refer to this post. This should clear things up on how the check valve works.
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4SPC, My 4" piston 3" porting cannon
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Unread postAuthor: Sticky_Tape » Fri Feb 06, 2009 9:05 pm

You olny need one check valve. You have to build a floating o-ring piston if you can't make a 100% seal on the piston.
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Attachments
floating oring..jpg
There you go it shows you how to make one in gippeto's how-to. The o-ring seals because the air pressure exspands the oring to seal on the chamber walls and also pushes the o-ring onto the piston to seal on there. on the up stroke the piston unseals and lets air into the cylinder like a check valve.
floating oring..jpg (9.02 KiB) Viewed 296 times
You can tell how awesome a cannon is by the pressure used.
http://www.spudfiles.com/forums/high-pr ... 12803.html
xnt rnm ne z ahtbg
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Unread postAuthor: daniel323 » Fri Feb 06, 2009 10:21 pm

thank you everyone i think i am going to attempt to build my stirrup pump now
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