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The limit for shock pumps?

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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The limit for shock pumps?

Unread postAuthor: inonickname » Sun Aug 09, 2009 7:44 am

Well, many members now own the low-volume, high pressure shock pumps meant for inflating mountain bike shocks.

They are basically slow for most chamber sizes, but what would you believe to be the limit?(yes, there are slightly different sizes, but volume delivery is all about equal). They pump nearly effortlessly to 400 psi, but exactly how much volume will they deliver?

I've tried pumping up a 600ml soda bottle with one (in a blast chamber, why I didn't fill it with water who knows) and I eventually gave up before 50 psi.

I wanted to use a shock pump in the des-2. It has a total volume, including pilot of around 35cm^3. Too much for the average guy with a shocky?

Any thoughts on the subject?
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Unread postAuthor: jackssmirkingrevenge » Sun Aug 09, 2009 7:51 am

I don't even consider using my shock pump for chambers over a couple of cubic inches. One compromise soultion is to use a normal track pump or compressor to bring it to an intermediate volume then use the shock pump to "top up" but it's still a lot of effort compared to a specialised high pressure pump or fridge compressor.
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Unread postAuthor: inonickname » Sun Aug 09, 2009 8:25 am

So would the 2 cubic inches I'm asking of it be too much?

I can halve the chamber volume, dropping from 964 to 825 feet per second with the same projectile. Another benefit to consider, the exhaust would be at 30.2 psi, with a low volume. Hardly a loud report.

Any thoughts? Tough it out with 2, or drop it to 1?
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Unread postAuthor: jackssmirkingrevenge » Sun Aug 09, 2009 8:30 am

The biggest I've ever been comfortable pumping exclusively with a shock pump is around 3 cubic inches, the rest is down to personal stamina and what you consider "comfortable" ;)
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Unread postAuthor: inonickname » Sun Aug 09, 2009 8:34 am

I'll go one "^3 I suppose. If I used the 2+ "^3 then I'd probably use a lower average pressure, around 300 psi due to excess work in pumping.

Add that to the fact I get less blisters, a quieter report, probably moar accuracy and more shots in the same amount of time..It's a fairly easy choice.

Edit: Those simulations are also with heavy projectiles, so performance will be higher on average.
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Unread postAuthor: boyntonstu » Sun Aug 09, 2009 8:40 am

Lewis and Clark needed 1,500 strokes to fill their air rifle chamber to 800 psi.
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Unread postAuthor: inonickname » Sun Aug 09, 2009 8:47 am

boyntonstu wrote:Lewis and Clark needed 1,500 strokes to fill their air rifle chamber to 800 psi.


Lewis and clark got more than one shot.
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Unread postAuthor: ramses » Sun Aug 09, 2009 9:18 am

If you had a compressor handy, you could most likely adapt the shock pump to be the second stage in a 2 stage pump. Simply add a check valve to allow air from the compressor into the bottom, next to the stock check valve. If you fill the cylinder to 8 bar, you will pump 9x the volume in every stroke.

This mod would increase deadspace, thereby decreasing the compression ratio, but since you are feeding it with extra pressure, you would also be able to pump to a higher pressure.

The downside of this mod is that the pump becomes a pneumatic ram, so if your hand slips off the handle, you can expect quite a face full.
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Unread postAuthor: maverik94 » Sun Aug 09, 2009 1:58 pm

boyntonstu wrote:
Lewis and Clark needed 1,500 strokes to fill their air rifle chamber to 800 psi.

Crazy Bastards lol :D
I don't know, I pumped a chamber of about 3.5 cu" up to 250 psi with mine, but it took a while :)
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Re: The limit for shock pumps?

Unread postAuthor: spudtyrrant » Sun Aug 09, 2009 2:55 pm

inonickname wrote: They pump nearly effortlessly to 400 psi.

well i got a planet bike shock pump i i can tell you one thing its not effortless at 400psi it easy till about 250psi but up fom their its not "effortless" i'm not saying its had its just not easy i would feel comfortable with 2ci tho as long as reload time isn't of key importance.
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