13 replies to this topic

[Lt Stefan]

Ok. So there's the air tank, then the barrel. Let's just say we're dealing with a whole lot of air. And many barrels of different sizes for different projectiles. My gun will have interchangeable barrels ranging in size from 1/2" PVC to 3" PVC and everything in between. So my problem comes from getting air from the tank to the many barrels. I plan on using a threaded adapter for all the barrels. So from the tank comes the valve to the tube that leads to the barrel. My problem comes in what size vinyl tube to use. I don't know which one is better-- more volume (bigger tube) or more pressure (smaller tube). And also, if I knew which size to use (ratio-wise), since the barrels have such a size difference, it couldn't be a new tube for every barrel. So I ask you, what size tube should I use?

[A side of nerf]

Well,
if your dealing with launching large projectiles, your going to want faster flow. (bigger tubing)
and if you are launching darts, you are probably looking at 1/8ID to 1/4ID for higher pressure.


The main question is...is this dumping air into multiple barrels at a time?

If not,
You could make or purchase a valve that would...
+ let air flow from larger tubing when you put a larger barrel in, then turn a nozzle so it lets air from smaller tubing in when you put in smaller barrels.

An example of the valve I mean would be a Air Spliter, you can read about them on that catalog page.

[Lt Stefan]

Well,
if your dealing with launching large projectiles, your going to want faster flow. (bigger tubing)
and if you are launching darts, you are probably looking at 1/8ID to 1/4ID for higher pressure.


The main question is...is this dumping air into multiple barrels at a time?

If not,
You could make or purchase a valve that would...
+ let air flow from larger tubing when you put a larger barrel in, then turn a nozzle so it lets air from smaller tubing in when you put in smaller barrels.

An example of the valve I mean would be a Air Spliter, you can read about them on that catalog page.

Well is there a type of fitting that has an input of 1/4" tubing, and an adapter that goes out in either 1/4" tubing or another fitting that can go to either larger tubing sizes?

[A side of nerf]

Here is my recommendation, I would make my own valve out of a "hose faucet fixture"

Directions:
Here is an example of a Wye-Valve with two 1/8 tubing couplers. and a 1/8in air input.
You need to make one with two different sizes....

You can...
1) Dig around until you find one that is right for the application and pay upwards of $30.00
2) Contruct one. (see below)

For construction,
I advise modifying a Garden Hose Wye-Valve ($3.00 at your local ACE.)
All you would have to do is somehow seal the fittings listed below in the two holes where the hose would normally attach. Then attach your air tank to the other hole.

Materials:
+ Durable Nylon Single-Barbed Tube Fitting Adapter for 1/8" Tube ID X 1/8" NPT Male Pipe, Black
McMaster Part Key: 5463K243

+Durable Nylon Single-Barbed Tube Fitting Adapter for 1/4" Tube ID X 1/4" NPT Male Pipe, Black
McMaster Part Key: 5463K247

It should be fairly easy with some fiddling.

Cost estimate: $15.00

Edited by A side of nerf, 08 February 2009 - 12:21 AM.

[Lt Stefan]

Thanks you've been really helpful.

So far this is what I'm thinking:

Tank to that hose y or other y fitting via 1/4" tube.
One y goes out with a barb fitting and 1/4" tube.
The other goes to an adapter with barb fitting for 1" tube.
At the base of the barrel will be a 1" easy-connect fitting (the kind that snaps on and off).
You either put the 1/4" tube with adapters in that fitting, or the 1" tube with an easy connect fitting in there. That way, if it's a small barrel, the 1/4" tube will shoot air more focused to the barrel, and if it's bigger the 1" tube will shoot the air.

Or...

Is any of this necessary? Do I really need to have different size tubes?

Edited by Lt. Stefan, 08 February 2009 - 11:50 AM.

[A side of nerf]

Is any of this necessary? Do I really need to have different size tubes?

Well if you are going to be launching launching large projectiles, you will need large tubing.


Here is my reasoning:
Look at the post that a titan missile sits on...
It is at least 3/4 of an inch in Diameter.

Now think,
which would shoot farther?
+ A titan missile with a 3/4in hole resting on a 3/4 inch post.
+ A titan missile with a 1/8in hole resting on a 1/8 inch post.

the first one,
even though they put out the same air, the 3/4 inch dumps it faster than the 1/8 inch which would trickle out.

Your plan sounds great, however barbed couplers and quick disconnects can be costly.

How big is the largest projectile you would be firing?

Edited by A side of nerf, 08 February 2009 - 01:43 PM.

[Lt Stefan]

Here is my reasoning:
Look at the post that a titan missile sits on...
It is at least 3/4 of an inch in Diameter.

Now think,
which would shoot farther?
+ A titan missile with a 3/4in hole resting on a 3/4 inch post.
+ A titan missile with a 1/8in hole resting on a 1/8 inch post.


How big is the largest projectile you would be firing?

Vortex football as of now, maybe tennis ball.

But, my projectiles will be launched inside of a barrel, so they don't have such a short length that air can be transferred to them. If you know what I mean, kind of how the stock LS breech can only have a certain range due to the fact that the dart can't go more than 3" in the barrel, but with an an angel the range increases because the barrel was longer. That's how it will be for me.

[A side of nerf]

I have to agree partly with you bob, however I believe that in this situation, since he is firing a projectile from a barrel, a dump valve that can transfer air quickly through larger tubing without possibility of constriction through 1/8 tubing which I actually use.
Reasoning:

Smaller = better.

The problem with 1/8 tubing is even with a small kink that cuts air flow in half, you are now down to 1/16 of an inch which, quite blatantly...sucks.

All that matters is the velocity developed by the projectile during its time on the spigot (and momentarily after, if there's still air pushing).

Wouldn't that mean that better flow (1/4 inch tubing) would be a stronger force accelerating a larger mass in a smaller amount of time, thus giving the projectile a higher velocity.

Edited by A side of nerf, 09 February 2009 - 08:56 PM.

[Lt Stefan]

Well first off, I nonchalantly asked my science teacher "Which would give more power, air with a lower pressure through a bigger tube, or air with a higher pressure through a smaller tube?" He said smaller.
So I got to thinking that switching different tube sizes and different barrels and getting it all to seal would create, quite frankly, a mess. So I decided that I think I should use 1/2" tubing for everything, being that 1/2" is the diameter of my smallest barrel. That way I won't have to deal with all the switching.

Also, does anyone know of a good valve that releases all of the air from a tank at once that can be actuated from the outside?

If it helps, my tank (just a simple version for descriptions sake) will be 3" PVC with two endcaps and about 2.5' long. I want to pull on the valve via picture wire and have all the air come out through the 1/2" tube.

Thanks for all your help.

[Doom]

I've read through most of this thread and am a little confused by the terminology but I think I have an idea of what's being asked.

Use the largest diameter tube you can if you want tubing between the barrel and the valve. Or eliminate the tubing altogether and attach the valve directly to the barrel. I would suggest the latter. You want this because small diameters reduce flow. You want as high flow as reasonably possible to make the barrel pressure as high as possible to move the projectile as fast as possible.

The velocity of the air doesn't matter much. Dynamic pressure effects are minimal in Nerf guns. What matters primarily is the static pressure.

If you're having interchangeable barrels going from 1/2 inch to 3 inch, you should look into making separate guns because a gun that will work in that range will be terrible at the low and high ends of the spectrum.

As for valve suggestions, I'm a fan of quick exhaust valves. I'd also suggest looking around SpudFiles, the website I linked to, because it'll probably answer 90% of your questions rather quickly.

[Lt Stefan]

Ok. Well first, it looks as if the animation in your link is a three-way valve that is actuated how?

Secondly, I think I like the idea that all the barrels of different sizes are connected to some type of fitting/adapter at the base the is a good size for that diameter tube. From the air tank I will have adapters that the different sized tubes from the barrels fits in.

I cannot link the air tank up to the barrel directly due to a design feature I have that is a secret

Another question I have is how do I fit a fitting of some kind into the barrel?

I'm thinking (from barrel to tank) barrel, end cap with fitting through it, threaded adapter, adapter on the gun, an the tube for air goes into the fitting in the PVC end cap at the base of the barrel. The threaded adapter will go on the outside of the end cap.

[Doom]

You should read the page I linked to rather than looking at only the animation.

QEVs need a separate pilot valve for triggering. They can be very sensitive, triggering at a pressure drop of a few psi, so care should be taken when filling with a schrader valve or other valves that will let out air when disconnected.

[...]

As pressure is applied through input port 1 the poppet (yellow) shifts forward blocking the exhaust port 3 and allowing flow through output port 2.

When pressure is removed from input port 1 back pressure at port 2 unseats the poppet and allows flow through exhaust port 3.

Another question I have is how do I fit a fitting of some kind into the barrel?

The answer depends completely on the combination of fittings.

In general you just find fittings that'll get you to what you can attach the barrel with. For example, I use an aluminum tube for a bunch of tests and I fit in in thinwall 1/2 inch PVC pipe with electrical tape. Then I use a 1/2 inch adapter connected to a short nipple. It's not the most elegant solution but it works.

[Lt Stefan]

Ok I think I understand.. but what supplies the pressure to port one to activate it?

And is this the same type of valve as say, an at2k? If not, what is the at2k valve and would that or something similar work?

[Lt Stefan]

So is there a similar valve I can use?