SpudFiles

I am looking at building a SIMPLE and CHEAP high pressure pneumatic air gun, that will be filled via a shock pump. I want it to be made from common parts that i can get on eBay or from a hardware store. I would like to know what is the best way to do this, and have a few Q's.


Barrel: 1cm by 1 meter copper barrel
Fill: Schrader Valve
Chamber: ???
Ammo: Potato/anything that fits


1. Can a regular Schrader fill valve handle these pressures, if not what fill valve should i use.

2. What size air chamber should i use and how to make this using common parts (that i can get online or at bunnings). E.g pressure rated hose or brass/steel fittings???

3. Should i use a QEV like this:

http://www.ebay.com.au/itm/Pneumatic-Qu ... 1408wt_905

and if so how do i pilot it via a ball valve or a blow gun

4. Or a spring loaded ball valve, to keep it simple (already have the spring and a 3/4 27 bar rated ball valve)

any Criticism/ Ideas welcome

Thanks Jazzman56

ball valve have slow opening time. and if you use stronger spring to open it fast the whole gun will shake ,and 3/4" bv need more power to twist it open.

QEV 1/2" IS THE BEST FOR YOUR GUN
Schrader Valve can handle a lot of pressure.

the pilot can be blow gun ,he can handle 400 psi. and it will be more easy to open than BV .but BV give you better performance than blow gun due the huge air flow.

and you can build your own piston valve that can have the same performance as QEV if he will build .

and the chamber volume can be the same as barrel volume, what pressures you wanna use ?

far_cry.

I don't care what psi i use but it will be most likely upwards from 200psi, more than a standard track pump. I already have the copper barrel, a strong spring, a 27 bar rated 3/4 ball valve and a 3/4 inch compression fitting to fit it.

Where can i get a cheap blow gun from????

jazzman56 wrote:1. Can a regular Schrader fill valve handle these pressures, if not what fill valve should i use.

Yes

2. What size air chamber should i use and how to make this using common parts (that i can get online or at bunnings). E.g pressure rated hose or brass/steel fittings???

Not more than 20cm³ or so, otherwise you will die of old age before you get it up to pressure with a shockie.

3. Should i use a QEV like this

Why not this one? Cheaper and much better flow for your intended barrel.

and if so how do i pilot it via a ball valve or a blow gun

For 400 psi both will do.

4. Or a spring loaded ball valve, to keep it simple (already have the spring and a 3/4 27 bar rated ball valve)

This would mean avoiding pilot volume and waste, so if you can put it together well it would likely be more practical than the QEV for similar performance.

Once again JSR you answer everything to the point and exceptionable well. All while making me feel like i have the intelligence of a banana. Thank you for your input once again.

What about using the spring loaded ball valve for the trigger for the 3/4 QEV???

Any ideas for a pressure accumulator/vessel???

jazzman56 wrote:Once again JSR you answer everything to the point and exceptionable well. All while making me feel like i have the intelligence of a banana. Thank you for your input once again.

What about using the spring loaded ball valve for the trigger for the 3/4 QEV???

Any ideas for a pressure accumulator/vessel???

You can use galvanized iron pipe and fitting from bunnings for a tank, keep it small about 20-30ml because shock pumps are slow as fuck. Just get a blow gun from bunnings for your pilot valve mate, no need bothering with spring loaded ball valves.

jazzman56 wrote:Once again JSR you answer everything to the point and exceptionable well. All while making me feel like i have the intelligence of a banana.

You asked the right questions, there are worse bananas on this forum

What about using the spring loaded ball valve for the trigger for the 3/4 QEV???

I would say that if you're going to go through the trouble of spring loading the ball valve, don't bother with the QEV. In terms of flow and opening time (assuming a decent spring) you're not going to see a difference in performance, plus you have the advantage that all the air you put in is going out of the barrel as opposed to some being lost through the pilot.

Any ideas for a pressure accumulator/vessel???

A short length of 3/4" threaded pipe should do, one end into the ball valve and the other end capped with a hole for the schrader.

Keep the volume down though.

A 25cm³ chamber at 400 psi takes about the same effort to pump as a 50cm³ chamber at 200 psi, but the first one will give you better performance even though it's the same quantity of air.

If you don't have a shock pump already thisis a good model at a reasonable price.

Crna Legija


If the pressure chamber is only 20-30 ml how long can by 1cm barrel be. Would i get better performance using a track pump's lower pressure (160 psi) and a larger pressure chamber and a longer barrel.

BTW can a QEV be pressurised not on the pilot side but directly from the pressure chamber???

Thanks for everyone's imput

jazzman56 wrote:Crna Legija


If the pressure chamber is only 20-30 ml how long can by 1cm barrel be. Would i get better performance using a track pump's lower pressure (160 psi) and a larger pressure chamber and a longer barrel.

BTW can a QEV be pressurised not on the pilot side but directly from the pressure chamber???

Thanks for everyone's imput

download ggdt, read the Usage tab and then model your gun in it.

you will more power from a small high pressure chamber then a big low pressure one.

you can fill chamber side, but you will need to poke a small(1-2mm) hole in the piston then add a spring behind it, you will still need to pilot it from behind.

jazzman56 wrote:If the pressure chamber is only 20-30 ml how long can by 1cm barrel be.

For a 20mL chamber at 400 psi, up to about 6 metres

Would i get better performance using a track pump's lower pressure (160 psi) and a larger pressure chamber and a longer barrel.

What I always dig up in this case, have a look at this data for a virtual launcher modelled in GGDT - 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

BTW can a QEV be pressurised not on the pilot side but directly from the pressure chamber???

It needs to be modified, with a spring behind the piston and a small pilot hole.

So a 20inch3 chamber is equal to about a 328 cm3 chamber. Is this right or is it just a total volume of 20ml or 20cm3????

Thanks jazzman56