having a pump integrated into the gun question????

[jvw1979]

Hi All

Been lurking here a while and is busy planning a .22 calibre airgun, I want to try and keep it a self sufficient weapon by adding a pump into the design, now i've been looking through the forum and cannot really find a clear answer on this.

If i had a cylinder pump with the exact same volume as the charge chamber, in my limited knowledge of pneumatics it means that for every cycle of the pump i would be adding 1 bar pressure? is this assumption correct or am i missing something obvious? I mean it seems a little easy that after 50 pumps I would have 50 bar(725 psi) pressure... OUCH!!

Anyways any advice would be much appreciated. I will post pics next time and ask more stupid questions in the weeks to come.

Thanks for any help

[jackssmirkingrevenge]

.If i had a cylinder pump with the exact same volume as the charge chamber, in my limited knowledge of pneumatics it means that for every cycle of the pump i would be adding 1 bar pressure? is this assumption correct or am i missing something obvious?

http://www.chemistryexplained.com/Fe-Ge/Gases.html

Roughly speaking, that's now it works - half the volume and double the pressure. There are of course losses due to heating etc. in the real world. You also have to consider any dead space in the non-return valve.

One important factor to consider is pump head diameter, mutliply the cross sectional area by the pressure you intend to reach to see what sort of force you'll need to be putting on it, especially if you're pumping directly and not using a lever.

If you're feeling ambitious, you can go with a two stage design.

Anyways any advice would be much appreciated. I will post pics next time and ask more stupid questions in the weeks to come.

Stupid questions asked nicely usually get good answers, welcome to spudfiles

[warhead052]

Have a look at Brian The Brains counter balanced hammer valve. He has built a gun around the valve and has a pump built into it, and correct me if I am wrong, gets about 1 bar with every pump.

[Brian the brain]

I have and..It does.

[warhead052]

For once I got one of my facts right! By the way Brian, you really have done an awesome job on it.

Jvw, might I suggest taking a look at Gippetos pump how to, and then figuring out how to incorporate that into your design.

[jvw1979]

Hey thanks for the info guys. Just read through the build log for that BTB "windbuks" thats what they are called where i'm from.. Brian it absolutely astounds and amazes me how compact you managed to make everything.

Some liberal plagiarism will ensue.

Gotta love the interwebs! so much info.

I know people hate it when questions are asked that's been answered a million times before, but there is just so much information. I completely missed this particular gun, and its EXACTLY what I had in mind.

[Brian the brain]

When you say " windbuks" I feel obliged to let you know that I'm just 2km away from where they call my " luchtbuks" a " windbuks"



Not sure what they call it in Afrikaans...(SA)

Brian it absolutely astounds and amazes me how compact you managed to make everything

I could not go any smaller...well only by sacrificing chamber volume.
Compactness is my thing.
It's what I focus on usually...

I'm tempted to replace the pump section by a CO2 12 gram adapter to get it to be as small as possible, despite the benefits of free air.

By the way Brian, you really have done an awesome job on it.

Oh chucks...

[jvw1979]

Hey i'm from SA, so a windbuks is what they are called. 8)

Here is a picture of the Piston valve, just the pressure from blowing into it with my smokers lungs makes it actuate pretty well, still have to finish the hammer valve that will serve as my pilot valve. it is a solid steel piston, I read a lot about pistons being to heavy... im just afraid using plastics or the like will wear out a piston plenty fast, and I'm used to working with metal.. epoxy and plastic just seems a little awkward

I have another question. I have attached another picture of the barrel I have lying around, I see it's a .177 instead of a .22 unfortunately. It was a nasty 8 bux chinese springer, the barrel is rifled at least and a slight bit more sturdy that a copper pipe. too bad it's only a 177. It's probably a good idea to start on a small plinker as this is my first airgun anyways.

Now another question. this barrel is only 40cm long, is it worth using this at all or should I abandon this and rather go unrifled and longerl? opinions like a-holes I know... but it'd be nice to get a few more than just my own.

[Crna Legija]

how big is your chamber and how much pressure?

[jackssmirkingrevenge]

it is a solid steel piston, I read a lot about pistons being to heavy... im just afraid using plastics or the like will wear out a piston plenty fast, and I'm used to working with metal.. epoxy and plastic just seems a little awkward

A Delrin or Nylon piston would be perfectly adequate, the piston heads on springers are usually made of similar synthetic materials and take a lot of abuse, much more than a pneumatic will suffer.

At least if you want to stick to metal use aluminium.

I have another question. I have attached another picture of the barrel I have lying around, I see it's a .177 instead of a .22 unfortunately. It was a nasty 8 bux chinese springer, the barrel is rifled at least and a slight bit more sturdy that a copper pipe. too bad it's only a 177. It's probably a good idea to start on a small plinker as this is my first airgun anyways.

With medium to heavy pellets, a fast valve and reasonably high pressure, you will be able to fire at high subsonic speed in the 950 - 1050 feet per second range which would hypothetically be enough to knock a rabbit down at 60 yards.

Now another question. this barrel is only 40cm long, is it worth using this at all or should I abandon this and rather go unrifled and longerl? opinions like a-holes I know... but it'd be nice to get a few more than just my own.

Again, you will still get good performance using high pressure and a fast valve, it's worth the extra benefit of accuracy to use the rifled barrel.

[jvw1979]

Hi Legija,

Well at this point i'm still gathering parts, so everytime i see something that might work the idea gets designed around it. I plan on using a soda stream bottle it's around 500cc(30ci) estimate, and I'm planning on using as much pressure as I can muster up with a integral pump. The soda stream bottle is capable of 200 bar. But I doubt any hand pump I could make would be able to push it up to that. So i'm targeting 50(700psi) bar pressure.

[jackssmirkingrevenge]

I plan on using a soda stream bottle it's around 500cc(30ci) estimate

500cc is far too much for a single shot, remember you're always better off with low volume and high pressure, have a look.

[jvw1979]

I'm definately thinking of going semi auto with a revolver style magazine.

On that topic, I cant seem to find a scrap piece of unseamed steel pipe, and buying a whole 6m length of pipe to only use 15cm of it is a bit expensive. The price difference between seamed and unseamed pipe is ridiculous. else I would have stuck with a break barrel single shot with a small chamber, and just used 2 endcaps on a length of pipe. Then again... I love the mechanical challenge so I'd love to put as many "features" as possible.

So my piston is too heavy ... damn .. okay aluminium it will be then.

[Crna Legija]

wow 500cc way to big 8-10cc is plenty.

[Brian the brain]

I cant seem to find a scrap piece of unseamed steel pipe,

I used a front fork tube off a pitbike.
You might be able to get those cheap as a scrap part.