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Pump Project

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: Fnord » Sat Oct 23, 2010 9:03 am

saefroch,

If you have time I'd like you to do a little experiment on my behalf.
I'd like to know how many pumps it takes you to get a 3 cubic inch chamber up to 730-ish psi. I suppose you could do this easily by swapping one of the chambers on your Trident for a smaller one.

I've tried figuring it mathmatically but this isn't likely to be very accurate with real-world factors added.
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Unread postAuthor: saefroch » Sat Oct 23, 2010 10:05 am

Well considering I've never actually REACHED 730 psi it will take a while, but certainly I'll try. The biggest factor preventing accurate calculations (right now) is the complicated dead volume calculation and my erratic stroke length (which I'm fixing).

Working on the pump today, so I'll let you know if I get any results. :)
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Unread postAuthor: saefroch » Sat Oct 23, 2010 12:26 pm

Well the little 1/16" pin that was holding my pump handle to the pump head just snapped, right as I reached 800psi (:D). I think I"ll be replacing it with something softer than high-carbon steel, as the only real stress on the connection with a two-stage is pushing the two together, so little actual strength in the bond is required.

EDIT: Replaced pin with copper wire, holding just fine.

EDIT: Nvm that, took it to 800psi for a demo, then while just pressurizing the first stage later, the pin failed. Why did I ever think copper would be better than steel?????? Suggestions for a better pin material? I'd rather not replace the pin every time I take the pump to 800+psi...

Has anyone pushed a hand-powered pump higher than 800psi?
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Unread postAuthor: Selador » Sat Nov 20, 2010 10:08 pm

For the pin, get a roll pin. They are made for EXACTLY this sort of thing.

Also: the probable reason the pin is failing is because it is experiencing forces that it shouldn't. Probably from a sloppy connection.

Take the copper wire out. Set the handle on the shaft. Look through the hole.

Does it all line up ? Or does the handle get pushed up from the shaft just a bit, when you push the pin in ?

If the handle has to be moved at all, to get the pin in, then you need to drill again, and use a bigger size pin.

~~~

Do you have a Lowes near you ?

For the grease, go back to the plumbing department, which you should know by heart, by now... And look for some plumbers silicone grease.

This is by far, the cheapest silicone grease I have ever found.
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Unread postAuthor: saefroch » Sat Nov 20, 2010 10:23 pm

The current pin I'm using (a nail) is working fine, because the pin doesn't experience any net shear stress unless I leave the second stage in the up position. Which I am currently avoiding.

The hole I drilled lines up fine, but what do you mean by "experiencing forces it shouldn't?" If the current pin fails, I'll get a roll pin, but until then I can't be bothered.
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Unread postAuthor: Selador » Sat Nov 20, 2010 10:39 pm

saefroch wrote:The current pin I'm using (a nail) is working fine, because the pin doesn't experience any net shear stress unless I leave the second stage in the up position. Which I am currently avoiding.

The hole I drilled lines up fine, but what do you mean by "experiencing forces it shouldn't?" If the current pin fails, I'll get a roll pin, but until then I can't be bothered.


Actually, most nails work pretty good as replacements for cotter pins and roll pins.

:D

But I treat them like the spare tire. They are only there until you replace them with the proper pin.

The shear stress that you describe, is what I meant. I would bet that a roll pin will work, even when you leave the second stage in the up position.

I was going to go back and edit, and add pics of the roll pins and the grease. But since you replied, I'll post them here.

:)
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Unread postAuthor: Technician1002 » Thu May 26, 2011 10:14 am

Due to the rate heat radiates, Diesel of the lube oil should not be an issue unless you really slam it down. A fire piston requires a fairly sharp blow to get ignition. The pump should be no different.
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Unread postAuthor: wyz2285 » Thu May 26, 2011 4:03 pm

How does a multi-stage pump works? sorry can't help around here :oops:
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Unread postAuthor: cammyd32 » Thu May 26, 2011 4:15 pm

How does a multi-stage pump works?

what you mean like the pump on the previous page? if so......

from my limited experience with pumps I can tell you it work in this way;
the first pump compresses the air into a small chamber at medium pressures the second higher pressure capable pump then takes this compressed air in through its intake and compresses it to much higher pressures and puts it into the chamber you want pressurizing.
it essentially allows you to pump to higher pressures faster. :D
(please correct me if I am wrong, I have very limited experience on this topic) :D
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Unread postAuthor: wyz2285 » Thu May 26, 2011 4:34 pm

Oh ok... I thought it was more complicate than that... But thanks anyway :)
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Unread postAuthor: Technician1002 » Thu May 26, 2011 6:02 pm

The second stage is only a fraction of the first stage in size. The first stage typically compresses the air to 1/10 its original volume. The second stage then can boost that again by about 10. This will take air from 15 lbs absolute (atmospheric pressure) in the first stage and raise it to about 150 PSI, then the second stage takes that up another 10x with 1/10th the displacement to raise it up to 1,500 PSI.

This is almost impossible with a single stage pump.
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Unread postAuthor: wyz2285 » Fri May 27, 2011 2:20 am

Só i have to pump the first stage first stage than pump the second stage? It's the same thing as us a big shock pump
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Unread postAuthor: saefroch » Fri May 27, 2011 8:34 pm

Yes, and the second stage should have a smaller diameter pump head, or it is almost ineffective.

What's this about a big shock pump?
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Unread postAuthor: Alster370 » Sat May 28, 2011 9:42 am

would there be two pistons on the same rod or would it be just one piston for both stages? :?
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Unread postAuthor: wyz2285 » Sat May 28, 2011 9:46 am

If I have a long shock pump, I would get the same pressure as a normal shock pump but more out put of air right?
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