2 defective diaphragms...or I'm doing something wrong

schadenfreud · Thu Dec 27, 2012 4:33 pm

First of all, I'd like to say that this site is beyond words in how phenomenal it is. I've been reading everything I can find here

Now then, my current project. This is my second pneumatic cannon, the first one I built years ago with my dad.

When doing some research for this, I decided to try a modified sprinkler valve.
Without doing enough reading, I picked up a chamber-sealing valve, got rid of the guide rod and tried it out. Air came out of the other end of the blowgun. Then I found this site and did a lot of reading.

Confident in what I learned, I bought an orbit 1" (model 57101 if that matters), tapped a blowgun, epoxied the solenoid holes and waited patiently for it to cure. I hooked it up to my chamber, then it would just leak out of the barrel.
Thinking I had a defective diaphragm, I picked up another valve. I put the diaphragm in the modified valve and hooked it up, same issue.
Just to be sure, I cleaned the valve and diaphragm and used some white lithium grease in the seal, but still no luck.
Any comments or suggestions would be greatly appreciated and my apologies if I missed this solution somewhere else on the wiki/forum

Side note: anyone else have problems with the screws on orbit valves? Both valves I picked up it seemed like the screws were already partly stripped

wyz2285 · Thu Dec 27, 2012 7:11 pm

Sounds like you mounted the valve backwards... But somebody else will help you better, I never used sprinkler valves.

D_Hall · Thu Dec 27, 2012 7:33 pm

First guess agrees with wyz....valve mounted backwards.

Beyond that... Pictures. We need pictures.

jackssmirkingrevenge · Fri Dec 28, 2012 12:36 am

How are you filling the chamber? Some sprinkler valves need to be "shocked" into sealing, so if say you have a very large chamber and bicycle pump it's not quite going to cut it.

schadenfreud · Fri Dec 28, 2012 2:30 pm

Thanks for the quick replies!

I had the valve so the output was towards the barrel, but just for giggles I tried it the other way, same issue.

Not sure what you gents prefer in terms of photo uploading, so here is a link to an imgur album

Chamber is filled with a schrader valve and a Husky 120 volt inflator.

D_Hall · Fri Dec 28, 2012 2:40 pm

Put your mouth on the upstream side. Blow on it as hard as you can. Does it seal? If so, then jack's probably right - your compressor just isn't up to the task of sealing it.

Also, what is the big plug bolted to the diaphragm? Is that somethign you added or just a model I've not seen before?

dewey-1 · Fri Dec 28, 2012 9:02 pm

Your first picture shows a "jar top" valve.
You have two different diaphragms so you must put them in the correct valve.
Remove the white filter screen as shown.
Remove all the white grease you have put on. It is not on the sealing surface of the exhaust port.
Add epoxy as shown, this will prevent leak to barrel.

jackssmirkingrevenge · Sat Dec 29, 2012 12:41 am

Looking at your launcher, I would definitely say that poor compressor flow and large chamber are your problem.

Here's a trick you can try, remove the barrel and keep the valve outlet sealed with your hand or by pressing it on a rubber surface on the floor, and let the pump go for a few seconds, then let go and I'm willing to bet it will seal.

Either that or have a go at filling it quickly with a decent track pump.

Also, given your stubby barrel and tiny valve relative to calibre, I can tell you your chamber is far too big. The projectile will leave the muzzle long before most of the air in the chamber is released. I would cut it down to less than half of its current size.

One other thing as I can't quite make out the lettering on the pipe, are you sure it's pressure rated?

schadenfreud · Sat Dec 29, 2012 6:25 pm

D_Hall: it does seal, I don't know what that bolt is, but I removed it, thinking it was the filter described in something I read here (and the one dewey-1 points out)

dewey-1: please correct me if I am wrong, but isn't a jar top valve one where the lid screws on (like a jar)? this valve is an inline, with 8 screws securing it in place. Trying your suggestions now, but I'm not sure how the extra epoxy will help; the hole you refer to is already sealed by the epoxy in the solenoid hole

jackssmirkingreenge: I certainly made a mistake in chamber/barrel ratio. I realized I had it backwards after most of the fittings were in place. When you say tiny valve are you referring to the sprinkler valve or blowgun (or both)? The pipe is conduit PVC, schedule 40. I tried holding my hand over the outlet, didn't help seal it

PaperNinja · Sat Dec 29, 2012 6:29 pm

I'm pretty sure conduit is not pressure rated, just something you should know before you spend a bunch of time fixing something that wouldn't be safe to fire anyway.

dewey-1 · Sat Dec 29, 2012 7:52 pm

schadenfreud wrote: dewey-1: please correct me if I am wrong, but isn't a jar top valve one where the lid screws on (like a jar)? this valve is an inline, with 8 screws securing it in place. Trying your suggestions now, but I'm not sure how the extra epoxy will help; the hole you refer to is already sealed by the epoxy in the solenoid hole

My mistake if it is inline with 8 screws. I could not tell for sure based on the cannon picture.

Why the different diaphragms then? Different brand or model number?

The additional epoxy is to insure that the vent to the output side is filled.
If you look carefully at the valve output side you will see the vent hole.

schadenfreud · Sat Dec 29, 2012 8:08 pm

the short version: I may have bought a chamber sealing valve, lost the guide pin. Wanted something simple, so I just bought a barrel sealing valve (the orbit in the rest of the pics) and I'm leaving the other one to modify further when I have time to sit down and make a diaphragm and all the other things in the advanced modifications part of The Sprinkler Valve book.
I just noticed the vent hole when I was cleaning it haha.
I'll know if it works tomorrow

dewey-1 · Sat Dec 29, 2012 11:39 pm

These are the newer diaphragms for the 3/4 and 1 inch inline valves.
They changed the design of these valves slightly in the solenoid area of the lid.

http://www.orbitonline.com/products/Acc ... 22/28/627/

jackssmirkingrevenge · Mon Dec 31, 2012 5:49 am

schadenfreud wrote:I certainly made a mistake in chamber/barrel ratio. I realized I had it backwards after most of the fittings were in place. When you say tiny valve are you referring to the sprinkler valve or blowgun (or both)? The pipe is conduit PVC, schedule 40. I tried holding my hand over the outlet, didn't help seal it

If the pipe has a wall thickness of around 0.2 inches then you should be safe. The valve you are using though is tiny compared to the barrel bore and will result in mediocre performance, especially with such a small barrel.

What are you planning to launch with this thing, and at what velocity?

Again I'm fairly sure the problem with sealing is your anaemic compressor, is there any chance of you trying to fill it from a proper 150 psi shop compressor?

schadenfreud · Tue Jan 01, 2013 2:17 pm

No calipers, but the wall is pretty thick
All of my local stores only carry 3/4 and 1 inch valves, would like to replace in the future with a larger valve
Originally I wanted this to launch flour over a large area, velocity doesn't matter to me in this purpose
I fixed the sealing problem by adding a ball valve between the chamber and the sprinkler valve (it also acts as a safety) and adding epoxy to the areas referenced by dewey-1

Thanks everyone for all the advice, I should hopefully have pics by the weekend

2 defective diaphragms...or I'm doing something wrong

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