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Lever HP-pump.. need help with math / O-ring-Question

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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Lever HP-pump.. need help with math / O-ring-Question

Unread postAuthor: jean » Sun Jul 08, 2012 1:23 pm

hey guys

i need help

say i have to build a one-stroke-pneumatic, something like the Sharp Innova, with only one stroke to pump it up.

i have to pump up 30ml/2inch3 of air to the highest pressure i can get.
the length is 80cm/32inch (distance between pump head and lever end)
pump tube inner-diameter 32mm max.
any ideas
-how to do the math for the lever
-how much a floating o-ring can take
-how much effort a strong human can take to the lever

thanks
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Last edited by jean on Tue Jul 24, 2012 3:33 pm, edited 1 time in total.

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Unread postAuthor: jackssmirkingrevenge » Sun Jul 08, 2012 1:43 pm

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Unread postAuthor: jean » Tue Jul 24, 2012 3:52 pm

hi thanks jack
now after reading this i see that iam gone the wrong way...
what i have to do is construct a pump before.

now i need help
in the sketch you can see the pump with given mesurements
and my question is: how much force i can get on the piston?
and how can i do the math

jean
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Unread postAuthor: jackssmirkingrevenge » Tue Jul 24, 2012 4:18 pm

If I've got it right it should be (40 x 90)/10, so 360 kg.

With a pump ID of 32mm, that means a maximum of around 635 psi.

This might seem high but it will give you a very small volume.

The Parker Hale is to my knowledge the most powerful single stroke pneumatic out there, and performance is quite mediocre.

What projectile are you planning to fire and how fast?
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Unread postAuthor: jean » Tue Jul 24, 2012 5:05 pm

hi
do you mean 90 cm or 80 cm
and what is about this
http://en.wikipedia.org/wiki/Parallelogram_of_force
there are more force ?! isn´t it?
i don´t understand the math!

the projectile depends on the volume of air and pressure i can get with this pump design
also thinking about this to get more volume
http://www.google.com/patents?id=a_hMAA ... &q&f=false
airsoft bb or .177 pellets or maybe other bigger calibers.

the fwb 600 and other have only one stroke and shoots 170m/s with .177
btw it is an option to do a second stroke if more power is need.

jean
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Unread postAuthor: Fnord » Tue Jul 24, 2012 7:47 pm

I thought the whole point of this type of lever arm was to get the mechanical advantage to approach infinity as the pump piston approaches 'top-dead-center'.
The pressure should roughly double every time the pump is depressed half the remaining stroke, but the mechanical advantage should increase based on the sine value.

These two force curves are close enough to each other that the force required should be mostly even throughout the last third of the stroke, so calculate from there (or correct me if I'm wrong, I haven't studied the subject much).

You'll be limited by dead volume after that.
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Unread postAuthor: jackssmirkingrevenge » Wed Jul 25, 2012 12:41 am

jean wrote:hi
do you mean 90 cm or 80 cm
and what is about this
http://en.wikipedia.org/wiki/Parallelogram_of_force
there are more force ?! isn´t it?
i don´t understand the math!


That's not relevant in this case, what you have is one lever around a single fulcrum.

I would go for an inline pump with a small diameter (say 10-12mm).

Once you're pumping, the difference between 2 strokes or 10 is not really relevant. You also have to accept that while self contained is nice, it's a trade-off with power if you want minimum effort.

Have a look at the FX Independence design... http://www.tmdfish.com/bbs/thread-15214-1-1.html
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Unread postAuthor: Brian the brain » Wed Jul 25, 2012 11:17 am

I don't get the one stoke thing while making it multipump is only one simple valve away.

Anyway, what you should do is experiment.

You want the longest stroke but also the longest lever to get the most out of it yet minimise effort.

Make a prototype piston ( loose fit, it doesn't have to hold any air)
lever and crankshaft.
Now work out where to place the axles to get maximum stroke.
The piston should run from one end all the way to the other when you work the lever, hitting the checkvalve, or in a single stroke, the endcap.

Piston head and whatever you decide to put on the other end should fit together as much as possible.

Use the findings to make the actual assembly later on.
So...compressing a volume of gas into nothing is not going to happen.
In a multistroke the air is transferred to a reservoir, in a single stroke the dead space IS the reservoir.
How to work this out?

A would advise to use a solid body piston ( wich will keep it nice and centered, but split in two parts, joined by a threaded rod.( and with two nuts to lock the two halves in place)
This will make it adjustable.
If you feel that compressing the volume is to hard at maximum piston length, you can shorten it slightly and test it again and so forth.

because the pipe dimensions are set, all you can do is follow this method to get the most out of it.
Your bodystrength combined with the pump dimensions limits the power you can get out of it.Those factors are set, so all you can do it finetune it to make the most out of it.

Multipump just gives you more volume ( at most likely a slightly lower pressure as the checkvalve and reservoir eat up some of the piston travel)

More volume gives you less pressuredrop as the projectile travels wich means that the projectile is being pushed harder for longer.

The slightly lower pressure will be more than compensated by the larger volume.
If you would go for a multipump design you will get better results.
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Unread postAuthor: jean » Wed Jul 25, 2012 1:07 pm

thanks for the answers


Fnord that the way iam thinking .... sine value

jack the fx is nice! an inline pump....i like to use the mech to get high force. are you sure the sine isn`t relevant to the force??

btb thanks there many good things
the pump you have build.. what effort do they need?
how much effort can do a strong adult?

btw is there any way to run ggdt on win7 ? runtime error
it seems if jack isn´t wrongwith his math that 80ml at 625 psi ins´t so bad for an airsoft bb.
i am wrong?

jean
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Unread postAuthor: jackssmirkingrevenge » Wed Jul 25, 2012 1:34 pm

jean wrote:it seems if jack isn´t wrongwith his math that 80ml at 625 psi ins´t so bad for an airsoft bb.


You won't get 80ml though.

Imagine you chamber (including pump movement) is 20cm long, if the pump only moves 10cm, then you will get 80mL at 30 psi

If your chamber is 11cm long, you will get 8mL at 300 psi.

635 psi is the maximum pressure you can reach with a 40kg force on the lever, but the way you drew it with a pump movement of 10cm, then you can only get 635 psi with a final volume of about 2mL
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Unread postAuthor: jean » Wed Jul 25, 2012 3:01 pm

yep i understand and that is what i wanted to say-2ml 600psi-but isn´t it enough? a 50 cm .177 barrel was only 8ml in volume.
i like to go with higher pressure-lower volume to keep the noise down.

like to know the difference between 2ml/600psi and 1ml/1200psi in fps- higher ?!?

jean
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Unread postAuthor: POLAND_SPUD » Wed Jul 25, 2012 3:56 pm

i like to go with higher pressure-lower volume to keep the noise down.
good thinkin

like to know the difference between 2ml/600psi and 1ml/1200psi in fps- higher ?!?
Yes... it's as simple as that - Y.E.S.!!!
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Unread postAuthor: jackssmirkingrevenge » Thu Jul 26, 2012 12:16 am

jean wrote:like to know the difference between 2ml/600psi and 1ml/1200psi in fps- higher ?!?


Yes, here's the data from a virtual GGDT model I had done to "prove" the point:

in each case, we're talking about the same quantity of air, but in a reduced volume and therefore at higher pressure.

(chamber is of constant diameter but different length, projectile size, weight and valve flow/barrel length are constant)

20 inch chamber at 50 psi - 406 feet per second

10 inch chamber at 100 psi - 537 feet per second

5 inch chamber at 200 psi - 684 feet per second

2.5 inch chamber at 400 psi - 830 feet per second

1.25 inch chamber at 800 psi - 958 feet per second

0.625 inch chamber at 1600 psi - 1006 feet per second
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