first piston valve

kotabuuki · Fri Apr 15, 2011 6:53 pm

So my overall design and specs are a go?

as for pressure, i plan on shooting it anywhere from 60 psi-110psi.

I also plan on having several different size barrels, so is the 30" a good all around size for multiple size barrels?

also how do i calculate my flow coefficient? i know ggdt has that feature but i don't have a chronograph, and i didn't understand your link 100%. i get the basics of your post however.

side note, every time you talk about that cannon, i want one more and more .

Gun Freak · Fri Apr 15, 2011 8:56 pm

You could always add a female adapter on the chamber, that way you can add an extension when needed, but 30" is probably around the best for your purposes. Also I'd keep the pressure at a max of 100 psi, but thats just me.

About flow coef on GGDT, most people just leave it at 45.

mark.f · Fri Apr 15, 2011 9:24 pm

kotabuuki wrote:

Just a small suggestion,

At the bottom, where the street elbow connects to the tee, you can replace the male adapter with a 2" SCH-80 riser nipple. These are SCH-80 PVC nipples (DON'T get the polyethylene/etc. ones, make sure it is PVC) with threaded ends. Get one that has about 2-3" of smooth pipe between the threads. Measure the socket depth of the socket end of the street elbow, and cut this length below the bottom of one of the threaded ends of the nipples, and then solvent weld into the elbow. This will bring the barrel closer to the chamber (indeed, possibly too close, measure before gluing it all together), improving both looks and stability. Good barrel braces should be used as well, have you planned on these?

kotabuuki · Fri Apr 15, 2011 9:45 pm

Gun Freak wrote:You could always add a female adapter on the chamber, that way you can add an extension when needed, but 30" is probably around the best for your purposes. Also I'd keep the pressure at a max of 100 psi, but thats just me.

i have the male adapter going into the T to that if i need to make another chamber i can just unscrew this one and replace it.

mark.f wrote: Good barrel braces should be used as well, have you planned on these?

ummm, i'll stick with my current design for the time being. and yes i have thought about braces. I have plenty of wood or black acrylic i can make the braces out of and i just got a couple of 7" hose clamps to secure them. and if i need to secure it better i have several jumbo sized zip ties.

i plan on beginning construction this weekend. hopefully i'll have it build by Sunday so that i have some time to test it out and post some pictures.

Gun Freak · Fri Apr 15, 2011 9:56 pm

Yeah true, you could just make a new chamber if need be. There are such things as threaded street elbows too to make the valve connection more low profile.

Your supports sound good also.

Make sure you don't rush the construction. Take your time and make a nice launcher. Some people are so eager to build something then their cannon looks like crap.

Good luck, it's going to be a beast.

Technician1002 · Fri Apr 15, 2011 9:59 pm

The flow coef in GGDT, use %. In using true Coef, it varies greatly with size. % won't exceed 100. Coef will get very large in larger sizes of valves. A section in the wiki explains it some more.
http://www.spudfiles.com/spud_wiki/inde ... oefficient
Be sure to follow the link to the Wikipedia article on the subject if you want the full rundown on what CV is in exact terms.

kotabuuki · Fri Apr 15, 2011 10:13 pm

Gun Freak wrote: Make sure you don't rush the construction. Take your time and make a nice launcher. Some people are so eager to build something then their cannon looks like crap. Good luck, it's going to be a beast.

I've spent all this time trying to get opinions and have my questions answered and i've taken suggestions. You bet i'm going to take my time! this is for a school project, and i want to be able to destroy the competition by looks alone, none the less when i start shooting it.

so it has to be as streamline and slick as possible.

I'm getting my sprinkler valve tomorrow, is there any specific kind i have to get? and also while i'm at the store i'll look for the threaded street elbow.

Gun Freak · Sat Apr 16, 2011 9:35 am

I would reccomend the Orbit Inline Sprinkler Valve in 3/4" or even 1" which I used on my 2" piston valve. Home Depot always has those street elbows. They can be expensive though, like 4 and change for one.

Technician1002 · Sat Apr 16, 2011 10:56 am

A piston valve in a T is built much like a common valve called a Globe Valve. The % coef is typically near 45 so the GGDT default value is good. A sprinkler valve is most often quite a bit less. The total valve CV includes not just the orifice but the entire valve. The extra turns and edges in a typical inline sprinkler valve are the reasons for the lower CV value.

This is a design reason coaxial piston valves outperform pistons built in a T. The plumbing leading into the valve is eliminated.

kotabuuki · Sat Apr 16, 2011 2:54 pm

Gun Freak wrote:I would reccomend the Orbit Inline Sprinkler Valve in 3/4" or even 1" which I used on my 2" piston valve. Home Depot always has those street elbows. They can be expensive though, like 4 and change for one.

i got the 3/4". and i forgot to look for the street elbow

but i'm going to start measuring the pipe and sanding/priming in preparation for assembly.

Gun Freak · Sat Apr 16, 2011 2:55 pm

kotabuuki wrote:forgot to look for the street elbow

Happens to all of us

kotabuuki · Sat Apr 16, 2011 3:58 pm

oooh, so i know some of you expressed some concern about my piston. well my dad works for a company that works with acrylic, (a type of plastic). anyways i was in the basement and asked him if i could use some, and he said that i can use whatever i can find. so i started digging and i found this

its about 1 15/16 in diameter, and fits perfectly in my valve. i just have to cut it a little bit shorter, and it will be perfect.

edit: there, all fixed.

mark.f · Sat Apr 16, 2011 4:04 pm

kotabuuki wrote:its about 1 15/15 in diameter, and fits perfectly in my valve. i just have to cut it a little bit shorter, and it will be perfect.

1 and 15/15", huh? I guess that would fit in 2" pipe.

kotabuuki · Sat Apr 16, 2011 4:08 pm

mark.f wrote:
kotabuuki wrote:its about 1 15/15 in diameter, and fits perfectly in my valve. i just have to cut it a little bit shorter, and it will be perfect.
1 and 15/15", huh? I guess that would fit in 2" pipe.

yea, yea, yea...... i guess i hit the wrong button

I'll fix it then, lol.

Gun Freak · Sat Apr 16, 2011 4:47 pm

Does your dad have a lathe at his work? Is there any chance you could make it into a cup shape to decrease the mass?

first piston valve

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