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Shock Pumps/ MOAR PRESSURE

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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Shock Pumps/ MOAR PRESSURE

Unread postAuthor: saefroch » Tue Mar 30, 2010 10:05 am

I have built and am working on a pneumatic cannon with fairly low capabilities, and since it is build from schedule 40 steel and aluminum, I am now looking for some way to get over ~200 psi (low, I know) chamber pressure. I do not have ready access to a refrigerator compressor, but I am interested in their capabilities (on average), and the capabilities and ease of use for a shock pump. For example, what attachment system do I need for a fridge compressor and/or a shock pump to a chamber? Are shock pumps easy to use at ~400psi (a significant upgrade for now, I'll be looking at higher pressures and hybrids later) if you're filling a chamber that's got about 200 cu. in. of volume? Answers to all or any questions are appreciated.
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Unread postAuthor: ramses » Tue Mar 30, 2010 10:56 am

oh god. I had a spreadsheet around here somewhere... it's not very accurate, but good enough until I have time to learn C++...

Okay. It is currently v0.02 ish, so expect bugs. Input fields are highlighted in yellow.

Pressure in: the PSIG pressure you are feeding into the pump. Since you have a compressor, you should use two check valves at the base of the pump, and feed the "inlet" from your compressor. be careful, as you have a pneumatic ram if you decide to let go of the handle. Maybe restrict the flow

Target volume: volume of your chamber, plus everything after the outlet check valve as far as hoses/gauges/valves etc. goes. Cubic Inches

target pressure: the PSIG pressure you want to reach

cylinder Diameter: diameter of the pump tube Inches

stroke length: obvious. Inches

dead space: the ammount of water that would fit in the bottom of the pump if the piston was all the way down. cubic Inches

Max force required: How hard in pounds you have to push for the last stroke.

number of strokes: number of strokes required to reach target pressure. FOR AN ACCURATE NUMBER, YOU HAVE TO RECALCULATE A BUNCH. IIRC, it is F9. mash it.

Max strokes: broken; ignore it

pump volume: hmmm... cubic inch

Piston area: obvious... square inches
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Unread postAuthor: saefroch » Tue Mar 30, 2010 3:27 pm

Is the default inputted .75 the normal diameter for the piston seal head on a shock pump? Or is that just a random guess?

I'm loving the spreadsheet, totally keeping that.
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Unread postAuthor: Hawkeye » Tue Mar 30, 2010 5:22 pm

I would guess a shock pump has a piston head closer to 3/8". A chamber much larger than a large cigar will take you forever to pump up.
I have gone on about the simplicity of making the 350 psi copper pump enough.
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Unread postAuthor: saefroch » Tue Mar 30, 2010 7:20 pm

I recently purchased a very good quality aluminium bike pump, $98. It's incredibly robust, but the gauge only goes up to 160psi. So i'm hesitant about going past the gauge, since that usually breaks the needle and runs the risk of breaking the pump. I'm looking for a good way to pressurize a large chamber to high psi. Any suggestions?
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Unread postAuthor: jackssmirkingrevenge » Tue Mar 30, 2010 11:48 pm

I certainly wouldn't recommend shock pumps for chambers larger than than a couple of cubic inches (unless you found a way to motorise it, which would be an interesting and not that challenging project)

If you don't have access to a fridge/AC compressor you might want to consider making your own stirrup pump, which is basically making an oversized shock pump with much greater stroke volume. Gippeto offers an excellent tutorial on the subject here.
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Unread postAuthor: saefroch » Wed Mar 31, 2010 10:03 am

You da man, JSR. That's exactly what I wanted to know. I'll certainly look into motorizing a shock pump, mostly because of the rated pressure tolerance on those things, I bet Ive got an old lawn mower engine somewhere that nobody would miss...

So that stirrup pump just screws directly onto the gun itself?

Is there any way to make one of those out of steel so it could handle higher pressures? It's probably possible with a welder and some good tools, but I'd like to be sure there aren't any other issues before I even think about trying.
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Unread postAuthor: jackssmirkingrevenge » Wed Mar 31, 2010 2:48 pm

If you're looking to adapt the shock pumpthis FX designmight be worth copying.

Image

The mechanism should be self explanatory.

If you make your own stirrup pump, it would probably still be worth buying a shock pump go cannibalise it for schrader attachment, hose and gauge, and I think it's safe to say that you would die of old age before reaching the sort of pressure that would make the materials that Gippeto used fail ;)
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Unread postAuthor: POLAND_SPUD » Wed Mar 31, 2010 3:04 pm

I've seen it before.. pretty much as simple as it gets... personally I'd use as small piston as possible (in order to reduce stress) and find some way to allow this thing to operate continually
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Unread postAuthor: daberno123 » Wed Mar 31, 2010 6:07 pm

Here's somebody else who took an FX airgun pump and motorized it...http://www.steelplinkers.com/LowbuckCompressor.html

Pretty simple actually, especially it you have access to a lathe...
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Unread postAuthor: Hawkeye » Wed Mar 31, 2010 6:57 pm

Even the old Girandoni guns from the 1700's used a pump system like this to fill the cylinders. Obviously not motorized but it did use a similar system that eliminated manual pumping.
I have a diagram of the system in an old Arms and Armor review.
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Unread postAuthor: Crna Legija » Wed Mar 31, 2010 8:41 pm

you can also try reged HPA or Co2. but getting a 40ish buck ac compressor of ebay it your best bet since you will only go to 200 psi
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Unread postAuthor: saefroch » Wed Mar 31, 2010 9:05 pm

I've already got the capacity to reach 200 psi. I've approximated measurements above the gauge on my bike pump. I'm looking for 400+ gpsi.
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Unread postAuthor: Crna Legija » Wed Mar 31, 2010 9:32 pm

well HPA Co2 and ac compresors will all go above 400psi
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Unread postAuthor: saefroch » Wed Mar 31, 2010 10:49 pm

but getting a 40ish buck ac compressor of ebay it your best bet since you will only go to 200 psi


Then where did the 200 psi come from? I'm confused....
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