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high flow shock pump

A place to ask general spud cannon related questions.
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will it work?

yes
3
50%
no
0
No votes
*ouch*
2
33%
maybe
1
17%
 
Total votes : 6
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high flow shock pump

Unread postAuthor: ramses » Wed Jul 30, 2008 11:58 am

When designing a shock pump, you have to have a small piston cross section to reach high pressures. you also have limits on the travel of the piston. you can't pump effectively with a travel of 3 ft, unless you play pro basketball. With a .5 diameter chamber and a piston travel of 18", your volume per stroke is a pathetic 3.5325 cu in. for a 35.325 cu in chamber, that will take 10 strokes per atmosphere, and take a really long time to pump up. for 11 bar, that is 100 strokes. If you were to hook up the intake of the pump to an air compressor, each stroke could have, assuming a 10 bar compressor, 10x the volume and it would take 10x less strokes to pump up the chamber. This would, assuming once again the .5" diameter piston, ~29 pounds lifting force on the piston. As long as your face or crotch isn't over the handle on the down stroke, you are fine, otherwise: :) =:male: :shock: :sad2: :crybaby: :oops:, :sign10: :sign6:, :)= :walk:.

Now that that's over with, does anyone see any problems with this, besides the danger of un-wanted birth control? :D
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Unread postAuthor: mobile chernobyl » Wed Jul 30, 2008 12:10 pm

Sure it'll work, but it will also just be that much harder to pump. You can't escape the conservation of energy theory. That is why they are so small in dia. to begin with. But I'm sure u already knew this.

Your idea is what is used in 2-stage compressors. Big piston compresses air from 1 atmosphere to around 60-80psi, then a smaller piston takes that and pumps it up to 150 or higher.
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Unread postAuthor: ramses » Wed Jul 30, 2008 12:16 pm

Sorry, Idon't quite understand why it would be harder to pump. I see where you are coming from with conservation of energy, but could you please elaborate on why it would be harder. Thanks
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Unread postAuthor: psycix » Wed Jul 30, 2008 1:20 pm

It will work, but there are a few things:
-Pneumatic ram danger. As you already suspected.
-You can also fill up the gun with 10 bar, and then pump it up further using a normal shock-pump design.

It will not be "that hard" to pump, the only difference is that there is 10 bar at the beginning of your stroke, and x bar at the end of it, while a normal shock pump has 0 bar at the beginning of the stroke, and x bar at the end.
It will not be much harder to pump, as x bar still is x bar. (as much as you can force out on the piston).
So its just the start of the stroke where things have changed, but since the handle is up at that point, you may not be optimally capable of putting your body weight on it to do the job.
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Unread postAuthor: mobile chernobyl » Wed Jul 30, 2008 1:50 pm

Air pressure does not compress in a linear fasion. It is progressive (ESPECIALLY progressive as the overal volume decreases)

psycix - your explanation has an error in it.

If you start one with 0Psi (1 atmosphere) and another with 90psi (compressor), you will not have the same amount of force at the end stroke of both. 0psi may compress to 60psi, thats .1963sq in (area of piston) X 60 psi = 11.75lbs needed to compress it to end stroke. If the 90psi compresses to 120psi, thats 23lbs pushing back at end stroke.

Thats only after one pump, and mind you those numbers aren't perfect, they are just examples. The numbers will not increase in a linear fasion, so don't expect differences to be consistant unless you are using exponential calculations.

::EDIT:: and ultimately, a highflow shock pump is a redundant term unless the pump is a high pressure air tank. Shock pumps are low volume by nature, and low flow to achieve mechanical advantage in creating higher pressures at lower volumes.

Base line, it WILL be harder if you add air pressure at beginning stroke, just use your head haha its not that hard to imagine it. Will it be impossible to compress? Maybe not if your a machine, this technique is used in multistage aircompressors the world over.
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Unread postAuthor: Gippeto » Wed Jul 30, 2008 1:56 pm

@ Mobile C

When the pressure required to open the check valve (cracking pressure + chamber pressure) is reached the check valve opens.

Ultimately, this is what determines pumping effort.
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Unread postAuthor: Hawkeye » Wed Jul 30, 2008 1:56 pm

I always thought making a shorter pump with two cylinders would solve the problem of having a ridiculously long pump stroke.
Link the two pump handles and link the outlets.
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Unread postAuthor: POLAND_SPUD » Wed Jul 30, 2008 2:56 pm

In theory the same principle can be used with fridge compressor by hooking its air input with a regular shop compressor... well at least that's theory because no one has tested it yet... (at least not here)


@mobile chernobyl
hmmm imagine that there is a big room filled with air at 147 psi... a generic stirrup pump can pump to 10 bar.. when it is inside the room the pressure acting on both sides of the piston is basically the same (before you start pumping)

so when you pump the pressure increases 10 times but the air you are pumping is already at 10 bar so the output pressure is 100 bar

Am I right ?
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Last edited by POLAND_SPUD on Wed Jul 30, 2008 3:17 pm, edited 1 time in total.
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Unread postAuthor: ramses » Wed Jul 30, 2008 3:09 pm

@polandspud-that was my basic idea.
@psycix- I suppose i will just have to use a shorter stroke, then.
@mobile C- I just realized that conservation of energy doesn't necessarily apply, because the shop compressor uses electricity to pump.
EDIT: it does apply, because it is "hard" to pump for the full stroke, rather than just the last "part"
@ Hawkeye- Your idea would produce results similar to doubling the surface area of the piston.

I don't suppose it would be practical to start putting fridge compressor pumps in series, would it?

Can anyone think of a way to prevent the pneumatic ram effect if I go through with this? to pump up a hybrid with a ~130 cu in chamber, and with a normal shock pump, .5" diameter, 18" stroke, that would be around 36 pumps per x, not fun.
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Unread postAuthor: VH_man » Wed Jul 30, 2008 5:11 pm

whatcha doin with a shock pump and a hybrid?

and BTW, its really not that bad.......... i have a 1/2 inch bore shock pump, and really, its so easy to do that i can sit the thing on the floor, sit down in a comfy chair, and pumpy my cannon to 300 while watching TV.

if you made a 3/4 inch bore shock pump, i think youll find it works better than youd expect.

and getting 3 or more fridge compressors will do it, yes, but have fun plugging all of them in......
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Unread postAuthor: brogdenlaxmiddie » Wed Jul 30, 2008 6:06 pm

Oh my god, I just was talking about doing this same thing to elitesniper just literally last night... :roll:
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Unread postAuthor: Gippeto » Wed Jul 30, 2008 6:54 pm

Have you ever heard of a beam engine?

http://www.keveney.com/watt.html

Replace the crank and flywheel with a smaller diameter cylinder fed by the larger cylinder, and you have a two stage pump.

Add a longer handle to get the force required for larger cylinders.
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Unread postAuthor: kablooie » Wed Jul 30, 2008 7:33 pm

The two-stage air compressor idea can (and has) been converted to hand pump use, mainly with this pump:
http://cgi.ebay.com/ws/eBayISAPI.dll?Vi ... %26ps%3D42

It's kinda pricey, but I have it, and it is the perfect solution to pumping to high pressures quickly. You can also use it for entirely low-pressure-high-volume situations too. Hope this helps.
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Unread postAuthor: psycix » Fri Aug 01, 2008 4:07 am

mobile chernobyl wrote:psycix - your explanation has an error in it.

If you start one with 0Psi (1 atmosphere) and another with 90psi (compressor), you will not have the same amount of force at the end stroke of both. 0psi may compress to 60psi, thats .1963sq in (area of piston) X 60 psi = 11.75lbs needed to compress it to end stroke. If the 90psi compresses to 120psi, thats 23lbs pushing back at end stroke


There is no error in my explanation. Why would 0 psi compress to 60? The maximum pressure of a single stroke is determined by the volume covered by the piston, and the dead volume.
If your pump has no dead volume (ideal pump) you could compress up to unlimited psi with both 0psi or 90psi starting pressure.
And on top of it. If I wanted to have my gun at 120 psi, then it does not matter if I use 90 psi as starting pressure or not. The end of the last down stroke just has to be 120 psi, which is 23 lbs in both cases.
You are now suggesting that the pump without starting pressure is easier to pump because 60 psi is lower then 120, but in the end, I still may want to get up to 120psi, and it does not matter if I use an pre-pressurized pump or not.
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Unread postAuthor: far_cry » Sun Aug 31, 2008 7:49 pm

lol
the members well think that i take your idea
take a look
http://www.spudfiles.com/forums/a-plan- ... 15814.html
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