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Short question topic

A place to ask general spud cannon related questions.
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Re: Short question topic

Unread postAuthor: hectmarr » Tue Dec 26, 2017 7:34 am

Cthulhu wrote:Quick question regarding pumps:
Has anyone found a pump that works by rotating a crank rather than the regular up-and-down piston that are so common?
A friend of mine built a little sheet metal "tank" and wanted me to build a pneumatic cannon for it, but the tight quarters inside make using a pump difficult and bringing a compressor impossible.

Only electric compressors have this system, the kind they use to pump air into the wheels of automobile tires. I imagine that you could build one with the features you need or use directly one of those that can be purchased. With a lithium polymer battery of good power, it would be quite compact.
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Re: Short question topic

Unread postAuthor: jackssmirkingrevenge » Thu Dec 28, 2017 6:55 am

These pumps tend to have a very small volume so if you're going to convert it to a hand crank, it would have to be geared up considerably otherwise you'll be cranking forever.

To be honest I think you're better off with a large paintball bottle or SCUBA tank + regulator.
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Re: Short question topic

Unread postAuthor: hectmarr » Thu Dec 28, 2017 4:59 pm

Hi Jack Yes, these compressors have a reduced flow rate. I bought one and it takes a long time to fill a chamber of just 50 ml at 7 bar. Maybe a bigger one, depends on the application.
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Re: Short question topic

Unread postAuthor: Cthulhu » Fri Dec 29, 2017 5:06 am

jackssmirkingrevenge wrote:To be honest I think you're better off with a large paintball bottle or SCUBA tank + regulator.


Yeah, a regulator for my paintball tank is on my list of things to buy (along with a real compressor).
Sadly since my income is based on selling my old Spudguns I run on very little cash :cry:
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Re: Short question topic

Unread postAuthor: jackssmirkingrevenge » Fri Dec 29, 2017 7:29 am

I would stretch the budget to something like this + car battery, otherwise you're going to be like the poor fellow cranking away inside the "Turtle":

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Re: Short question topic

Unread postAuthor: Cthulhu » Fri Dec 29, 2017 8:20 am

jackssmirkingrevenge wrote:you're going to be like the poor fellow cranking away inside the "Turtle"


That's really funny because the tank my friends and I are building is pedal powered like a bike, so no matter what someone will be cranking away!

Good idea though, I'll look into those nice little pumps.
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Re: Short question topic

Unread postAuthor: jackssmirkingrevenge » Fri Dec 29, 2017 9:04 am

Viair is a reputable brand you should be looking at, avoid those cheaper Chinese made tire inflators.
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Re: Short question topic

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Re: Short question topic

Unread postAuthor: Cthulhu » Mon Jan 01, 2018 12:29 pm

If I use a 1" sprinkler valve for a 3/4" barrel, will that have better or worse performance than a 3/4" valve for a 3/4" barrel?
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Re: Short question topic

Unread postAuthor: jrrdw » Mon Jan 01, 2018 2:22 pm

Cthulhu wrote:If I use a 1" sprinkler valve for a 3/4" barrel, will that have better or worse performance than a 3/4" valve for a 3/4" barrel?


It might be a little better, wouldn't be any less, there's no choke point in between valve and barrel.
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Re: Short question topic

Unread postAuthor: Air2theBrain » Fri Jan 05, 2018 7:53 pm

Would anyone know how much pressure a 30g Co2 cartridge can hold?

I have a 88g co2 cartridge for the main tank, and want to use the 30g for the air chamber.

If it could hold between 200psi-300psi that would be great. 8)
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Re: Short question topic

Unread postAuthor: Gippeto » Fri Jan 05, 2018 8:53 pm

CO2 is around 850psi at room temperature...300psi shouldn't be a problem for the co2 canisters.

Pay attention to everything ELSE that handles the pressure though...make sure it's up to the task.
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Re: Short question topic

Unread postAuthor: Air2theBrain » Sat Jan 06, 2018 3:10 pm

Gippeto wrote:CO2 is around 850psi at room temperature...300psi shouldn't be a problem for the co2 canisters.

Pay attention to everything ELSE that handles the pressure though...make sure it's up to the task.


Will do and many thanks for the reply Gippeto. :)
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Re: Short question topic

Unread postAuthor: Anatine Duo » Sun Jan 14, 2018 10:27 pm

Having a look inside some pressure rated sched 40 1.5" pvc and it isn't nice... kinda bumpy. Still smooth but like cellulite almost. Is anyone else's like that or did mine get contaminated? It's not a candidate for cast in place pistons/endplugs :(
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Re: Short question topic

Unread postAuthor: jackssmirkingrevenge » Mon Jan 15, 2018 7:12 am

Anatine Duo wrote:It's not a candidate for cast in place pistons/endplugs :(


This has always been my experience, which is why I typically would cast the body of a large syringe for a piston housing, for example for this one:

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Re: Short question topic

Unread postAuthor: notarobot » Tue Jan 16, 2018 12:57 pm

And suddenly it all makes sense.
Thanks JSR.
Reading the posts over the past few months, I have come to be able to follow the explanations, but with that illustration, now I understand the science.
It's so simple.
You could look at that as a lopsided coaxial as well.
The reason went with manufactured valves is because I was looking for a formula or recipe to follow. You know, plans of something that works; guaranteed success.

I suppose I had better finish my metal QEV build soon, 'cause I am think I want to try a few new ideas.
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