Air Vent Question (New Pic's) Please Look

Post questions and info about combustion (flammable vapor) powered launchers here. This includes discussion about fuels, ratios, ignition systems and anything else relevant to launchers powered by igniting things like hairspray or propane.

Postby Robcsmall » Tue Dec 05, 2006 3:58 pm

Hey, I'm building a propane launcher. My question is about safety. I plan to have a spring loaded rubber plug in the bottom of my launcher (AUTO AIR INTAKE) These are those squeeze compress the rubber type of plug. I got about 4-5 bucks and 10 min of time in each.

>
<img src="http://i147.photobucket.com/albums/r318/robcsmall/100_1529.jpg">

>

I cast polyurethane rigid plastic between the out side of the plug and the inside 4" threads of the fitting. (The polyurethane is like two part epoxy except higher flex modulus.)
<img src="http://i147.photobucket.com/albums/r318/robcsmall/100_1530.jpg">

>
I will brush on a parting agent on the threads. This way it will take on the opposite thread shape but will not bond to it. If I need to replace or access the chamber, I can unscrew the unit.

The rubber funnel looking thing is the air intake and seal when firing. I filled the rubber cone with a rubber polyurethane to stiffen the plug up.

Any thoughts on safety on this. I have used this method before with good success.
Robcsmall
 
Posts: 182
Joined: Thu Jun 01, 2006 4:20 pm
Location: USA
 

Postby SpudStuff » Wed Dec 06, 2006 8:59 pm

That should hold for the time needed. That is a really good idea! So there won't be a cleanout?
SpudStuff
 
Posts: 789
Joined: Sun Nov 20, 2005 2:06 am
Location: USA
 

Postby Robcsmall » Wed Dec 06, 2006 9:23 pm

Thanks,

The barrels will screw off and now that I think about it this part must unscrew so I can replace the batteries in the cheep walmart modified fan. So... if threads hold I guess this is a working model.

I'll have pic's soon in the finishes cannons.

<blockquote id="quote"><font size="1" face="tahoma,verdana,arial" id="quote">quote:<hr height="1" noshade id="quote">Originally posted by SpudStuff
[br]That should hold for the time needed. That is a really good idea! So there won't be a cleanout?
<hr height="1" noshade id="quote"></blockquote id="quote"></font id="quote">
Robcsmall
 
Posts: 182
Joined: Thu Jun 01, 2006 4:20 pm
Location: USA
 

Postby Robcsmall » Thu Dec 07, 2006 7:47 am

I'm Sorry, My question was a little vague.

I hope the new Pics help explain what I'm trying to accomplish.
Robcsmall
 
Posts: 182
Joined: Thu Jun 01, 2006 4:20 pm
Location: USA
 

Sponsored

Sponsor
 
 

Postby utcpyro » Thu Dec 07, 2006 5:54 pm

Seems safe to me, but you might not want to stand right behind it. Also, you'll probably need a really light spring on it witch MAY cause a little propane to leek before fireing and cause a small back flash, but not anything too major.
utcpyro
 
Posts: 1004
Joined: Wed Feb 09, 2005 12:45 pm
Location: USA
 

Postby natanddiane » Fri Dec 08, 2006 4:04 pm

Small back flash? Propane fires? YIKES! This rig spooks the snot outta me! I like my eyebrows and the other temperature sensitive parts of me
natanddiane
 
Posts: 13
Joined: Sun Dec 03, 2006 9:41 am
Location: USA
 

Postby Robcsmall » Sun Dec 10, 2006 10:35 am

<blockquote id="quote"><font size="1" face="tahoma,verdana,arial" id="quote">quote:<hr height="1" noshade id="quote">Originally posted by utcpyro
[br]Seems safe to me, but you might not want to stand right behind it. Also, you'll probably need a really light spring on it witch MAY cause a little propane to leek before firing and cause a small back flash, but not anything too major.
<hr height="1" noshade id="quote"></blockquote id="quote"></font id="quote">

The springs had to be changed out, the ones that come with the original unit were too weak. The new springs hold the seal (water tight). No leak when I filled the chamber with water.

They are still easy to hand compress or simply set the launcher on it's butt, and the weight of the launcher will compress the spring nicely.

I will cut notches or drill holes on the sides of the PVC fitting, behind the plug for air to get in.
Robcsmall
 
Posts: 182
Joined: Thu Jun 01, 2006 4:20 pm
Location: USA
 

Postby nicholai » Sun Dec 10, 2006 12:46 pm

hey that is an awesome idea! What if you wired some sort of switch into that plug so when you opened it a fan turned on? This would vent a lot faster than hitting a switch and opening a ball valve, or letting it vent through the barrel.
nicholai
 
Posts: 60
Joined: Thu Mar 02, 2006 11:05 pm
Location: USA
 

Postby Robcsmall » Sun Dec 10, 2006 2:33 pm

<blockquote id="quote"><font size="1" face="tahoma,verdana,arial" id="quote">quote:<hr height="1" noshade id="quote">Originally posted by nicholai
[br]hey that is an awesome idea! What if you wired some sort of switch into that plug so when you opened it a fan turned on? This would vent a lot faster than hitting a switch and opening a ball valve, or letting it vent through the barrel.
<hr height="1" noshade id="quote"></blockquote id="quote"></font id="quote">

Another good Idea!

Thanks
Robcsmall
 
Posts: 182
Joined: Thu Jun 01, 2006 4:20 pm
Location: USA
 

Postby DK » Mon Dec 11, 2006 3:24 am

Rob,

I think you've come up with an excellent idea. As for safety issues, I don't really see how there are any. Do you have any idea how much weight the threads will hold in the cast polyurethane? Try subjecting them to some light shock loads from the inside while the plug is screwed in and see what what effect they have (ie. how much the plug flexes). Then fire it a number of times and check for stress points in the poly. You could also check the shock force required to eject the cast plug from the coupling and compare it to the force generated on a typical threaded plug by the combustion of propane (or cleanout cap, since the thread depth is similar). I'm sure you know what you're doing, but you asked. ;)

I have a question for you though; How do you operate the plug? The spring looks too small to be used with the hand but resting it on the ground seems like an easy way to put unwanted dirt into the spring coils.
<blockquote id="quote"><font size="1" face="tahoma,verdana,arial" id="quote">quote:<hr height="1" noshade id="quote">"I will cut notches or drill holes on the sides of the PVC fitting, behind the plug for air to get in."<hr height="1" noshade id="quote"></blockquote id="quote"></font id="quote">
What do you mean by this? In the forward part of the coupling? and why?

Regards,
Harlan
DK
 
Posts: 178
Joined: Wed Apr 05, 2006 1:51 pm
Location: Canada
 
 
Next

Return to Combustion Launchers

cron