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homemade pump questions

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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homemade pump questions

Unread postAuthor: bigbob12345 » Fri Jan 11, 2008 11:01 pm

I know there have been lots of topics about this lately and you all are probably sick of it but I have a couple questions that the other topics didnt answer.
First what would be the perfect pipe size to use as the compression chamber if you wanted to be able to pump with high volume but have relitively low effort up to 100 psi.
Second what would be the perfect pipe size if you wanted to pump with as much volume as possible and with relitively low effort up to 300 psi.
Third is pvc safe to use in the pump mentioned in the first question.
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Unread postAuthor: Hawkeye » Fri Jan 11, 2008 11:47 pm

3/4 inch copper seems to be the best all around size and material. It is large enough to build volume quickly and the interior is the most uniform for a good seal and piston gliding surface.
You could use one inch copper if you don't want to go for really high pressure but I would just go with 3/4 inch because it can go to 300 psi easily as well. Then one pump can be used for a variety of pressure demands.
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Unread postAuthor: koolaidman » Sat Jan 12, 2008 12:28 am

yeah, i have been considering the same thing. I was planning on using 1/2 pvc pipe. first off i already did calculations. the inside area of 1/2" pvc (pi x .602^2^) x 100 psi = 114 lbs of force. Thats already a considerable amount of force so i wouldnt do a bigger diameter pipe. Also remember that your gonna have to attach check valves to it. Im planning on starting one in the next week, so lemme know how yours turns out and how you did it.
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Unread postAuthor: bigbob12345 » Sat Jan 12, 2008 12:29 am

well then I will make the high pressure one with 3/4in copper.But I would also like a high volume one.Would 1.25in copper be exceptable for a high volume one to get to 100 psi quickly.And would pvc be safe for that.

Edit:didnt see koolaidmans post
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Unread postAuthor: clide » Sat Jan 12, 2008 1:24 am

koolaidman wrote:the inside area of 1/2" pvc (pi x .602^2^) x 100 psi = 114 lbs of force.


You have to use radius or divide the total area by 4 if you use diameter.

Its pretty simple to figure out what diameter you need. If you are pumping right then the force you can exert effectively is your weight. So using the basic equation that force is pressure times area you can get an equation for diameter.

F = P * A
A = pi/4 * d^2

So solve that and you get

d = (4*F/(pi* P))^(1/2)

So if you weigh 150 pounds then you would plug that in for F and whatever pressure you need for P. And that will give you a maximum diameter of 1.38". Plug in your actual values to get the real number.

Edit: As for the PVC question. Pumps tend to get hot if you are pumping on them for awhile, although I'm not sure if it is hot enough to compromise the PVC. If possible I would suggest avoiding PVC because of the heat issue.
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Unread postAuthor: Hawkeye » Sat Jan 12, 2008 8:19 am

You will notice that track pumps are about an inch and a quarter in diameter.
I would definitely avoid pvc. The air in a pump gets hot enough to ignite flammable materials so repetitively using it will eventually compromise the material.
If you want to try moulding an epoxy piston, there are special epoxies formulated for high heat situations. That might not be bad idea. Certainly using hot glue for a pump piston would be a very poor idea.
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Unread postAuthor: bigbob12345 » Sat Jan 12, 2008 8:47 am

Thanks for the equation clide. And hawkeye would it be okay to use pvc rod for the piston or would that melt.
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Unread postAuthor: koolaidman » Sat Jan 12, 2008 5:57 pm

oh feces! you're right, i put in diameter not radius, silly mistake. I recognized the heat factor, yet im still not fully convinced that it would generate enough heat to get pvc up to its upper heat limit.
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Unread postAuthor: Hawkeye » Sat Jan 12, 2008 7:20 pm

Every pump stroke has the potential to ignite stuff (like a fire piston). By the time you get a chamber up to 350 psi the end of a pump is almost too hot to touch.
Initially I glued my copper pump with 'just for copper' and the heat eventually broke the glue down and caused leaking.
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Unread postAuthor: bigbob12345 » Mon Mar 17, 2008 9:10 am

Okay sorry for kicking up an old topic but I didnt think it was worth it to make a new one just to ask this.
Okay I need some way to attach the pump to the gun so I can pressureize it.
I was thinking of using a shrader valve but then i heard they leak at higher pressures so im wondering if I can use just the average hadware store quick connects at 300psi which is going to be the max I take it.
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Unread postAuthor: bigbob12345 » Mon Mar 17, 2008 4:31 pm

I really need to know the anwser to the above question.
If it doesnt get answered her ill make another topic for it but i dont think that is nessesary.
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Unread postAuthor: Sticky_Tape » Mon Mar 17, 2008 4:41 pm

maybe get somthing to screw onto the shrader I dont think shraders leak at high pressures hence shock pumps.
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Unread postAuthor: bigbob12345 » Mon Mar 17, 2008 4:44 pm

Are you sure they dont leak because Ive hear many times from many people that they do.
will quick connects hold the pressure is my main question because I like the easyness of use of the quick connects.
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Unread postAuthor: lockmanslammin » Tue Mar 18, 2008 11:23 am

I can say I have taken my brass quick connect to 300PSI and it hasn't failed yet. But, If you look in Mcmastercarr if my memory serves me correct, they are rated at like 250PSI, so I am probably pushing the envelope a bit.
Try it at your own risk.

Good luck on the pump
This is the pump I'm talking about

<a href="http://s117.photobucket.com/albums/o75/lockmanslammin/?action=view&current=trimmedpic.jpg" target="_blank"><img src="http://i117.photobucket.com/albums/o75/lockmanslammin/trimmedpic.jpg" border="0" alt="gun and pump"></a>
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