SpudFiles

Hi,

I am just building my first airgun, it will be an multishot or semi auto QEV 6mm. My airreservoir will be on the pilot side,so when I trigger the blowgun also air from the reservoir will blow out. The easiest way to fix this should be a ballvalve between the reservoir and pilot. So I got a second idea to get as many shots as possible: Just put instead of one ballvalve, two. Open the first let air flow up to the second ballvalve, then close the first. Now you've got a certain amount of air between the two ballvalves. When you open the second one you just got the "little" amount of air and lower psi instead of opening the main reservoir(example400psi). So you got a cheap regulator.

My main question is how I have to calculate the volume between the ballvalves to get my desired psi in the firing chamber?!

A bit difficult to explain, I hope you understand me

The volume of a cylinder is calculated with the equation V=Pi*R^2*H, V is volume, R is radius, and H is height. Do that for the inside measurement of the pvc and you have the approximate volume. To be more specific, the volume of a sphere is 4/3*Pi*R^3, so use that to figure out the volume around the ball.

Go here for a chart of PVC sizes.

I have no idea if psi goes down linearly with volume, and at what rate, so don't take it for granted that if volume is double psi is half. Do some research on that if you care, or just attach a pressure meter and test it.

And can I suggest using only 1 ball valve, so it would be like this:

Fill valve--Resevoir--Ball Valve--Firing tank--QEV--Barrel

With blowgun attached to the firing tank. You could also replace the ball valve with a push button valve to speed up the loading.

Also, with each shot, the psi in the resevoir will be lower, and so it will have less power. Look up using Latex Rubber Tubing for a low pressure tank that keeps constant power over multiple shots. This is the best resource I know of for it.

You can also fill the area with water and drain it in a measuring cup to find the volume.

Should have remembered that.

Why not use a 3-way DCV?

Expense, simplicity, idk? The OP can do whatever he wants. Anyway, a good diagram for a DCV/QEV system is shown here.

you should get one of theses that will block off you big tank at the same time it will pilot the qev. so no need to 2 ball valves and in the other position will fill the tank on the gun

i used one im this gun

Crna Legija wrote:you should get one of theses that will block off you big tank at the same time it will pilot the qev. so no need to 2 ball valves and in the other position will fill the tank on the gun

Seconded, I bought a couple, haven't used them yet though.

How do those pilot the QEV? Are they supposed to drain the pressure from the marker into the air when closed, and then fill the marker when open? So it's a really compact 3 way valve?

EDIT: Yep, just like that. Nice find guys! These seem so much easier to attach an actual trigger than other DCVs.

http://www.legris.com/jahia/jsp/display ... n_coul.swf

Anyway personally I prefer 3 way valves with a lever or a button as that feels more like a real trigger.

Even if you choose a slide check valve you have to decide how to orient the QEV (where is the pilot/barrel port facing).

This is what I think works best for larger launchers:

The triggering valve (3 way) is exactly where it should be and the chamber acts as a stock. Also the barrel is higher than the stock/chamebr which makes aiming feel very instinctive

It might not work for you since your gun is 6mm cal. Though now that I think of it you might as well use a 1/4" 3 way piloted valve as the main valve. That might sound complicated - but essentially it comes down to:

1. get a 1/4" 3 way solenoid valve (piloted) - such valves have a smaller inbuilt valve that pilots the spool. Essentially the whole valve acts like a 3 way + QEV combo
2. attach a chamber to the middle port, barrel to the other one and air source to the last one
3. when you power the solenoid the spool will switch and fire the bb
...and that all

Thanks for all the answers!
But I do not want a 3way valve, I want my own, maybe new, design.
And my idea is to got a very simple regulator to get as many shots as possible.

My current setup:


For the chamber i got some more fittings to make it bigger( I first have to test whats the best size)
It is a 1/4" QEV, on the left there will be the reservoir, detechable via quick connect.

Be sure to take that nozzle off the end of the blowgun, it wont work very well otherwise.

Thanks, i know. It is just a quick put together.

Personally, I still prefer the chamber facing forward and with the magazine straight down.
The ram can even be placed else where using a rod extended backwards to cycle the action.

All of this allowing for a longer barrel, which does make quite a difference for pneumatics.
Obviously aiming without sights is harder, but that is quite easy to fix.


I reckon a blow through bolt in front of the QEV is more efficient in this type of setup, the QEV can be placed inline with the barrel with the bolt sliding back into it. The air ram can be a lot smaller, dead volume isn't too high and it avoids a bend in the airflow.
I must admit it is not as cool as the rear loading version though.


I have though a few other designs using air rams, suitable for synchronised select fire, but with a much more dynamic action for shell ejection and other cool but useless features. I was hoping to actually build a prototype before posting the ideas, as a proof of concept and illustration (a more reliable take on delayed blowback), but I still don't know when I'll be able to to that, might just give up and post the theory.


Finally an other thing that I reckon hasn't been tried enough, is mechanical full automatic fire using a 3-way valve using the air ram for synchronisation.

I want my own, maybe new, design

you see the wheel was invented a long time ago.Despite the fact that thousand of ppl tried to come up with something better it is still the best designs

hasn't been tried enough, is mechanical full automatic fire using a 3-way valve using the air ram for synchronisation.

@al-xg
You mean like this one ?