SpudFiles

I'm a filmmaker and one scene in an upcoming movie requires dirt explosions. I was thinking of building a simple, cheap pneumatic cannon, putting dirt at the mouth of the barrel, burying the main assembly and firing the dirt upwards. Is this a safe and effective method? Can any other methods be suggested? Thanks!

That would work just fine. You might think about using a metal barrel, for durability if you're going to be shooting rocks and dirt. I would be as safe as potato cannon can be, which is probably safer then explosive effects.

You should take a look a Joel's ThunderpipeFX1 that's exactly what it's for.

Nice, two links to the same page.

You should build a small coaxial. With loose dirt you might be able to put a 90 Degree elbow on the end of the barrel so you can just lay the gun in the ground instead of burying the whole gun.

Nice, two links to the same page.

rmich732 posted that link while I was writing a useful message.

I wouldn't send the time to make a custom valve, a simple sprinkler valve would have more then enough power.

The 90 degree elbow was what I had in mind. I've already seen the Thunderpipe and decided that it's a bit too expensive for my budget. Thanks!

You don't need to buy it. One with a bit of knowledge could built that or a similar gun for much less.

I wasn't planning on buying it. I just need a simple plan and a shopping list and then I'll be ready to go.

Better post some pics or better yet some vid of the scene

Anywho, Ill lay out what I think would be good. Starting at barrel, wrapping back to the chamber.

2' 2" sch 40
2" Coupling
2" Spigot x 1" FIP
1" MIP x 1" Slip (Elbow)
1" sch 40 [To get length measure socket depths of the one fitting and mulitply it by 2]
1" MIP x 1" Slip (Elbow)
Sprinkler Valve [Gonna need to decide on method of activation, seeing as pneumatic will provide better performance, while being hard-to-do by any 'cheap' methods]
1" Close NPT Nipple
2" Spigot x 1" FIP
4" Spigot x 2" Slip
4" Coupling
1.5' of 4" sch 40 [Want to cheap it fairly short to be sure the chamber doesnt extrude farther thent that of the barrel.]
4" Cap

Filling System- [Itll be slightly different since you dont have access to the buryed device]
1/4" NPT x 1/4" Barb
Length of 1/4" ID Hose
1/4" NPT x 1/4" Barb
1/4" Tee
Schrader Valve
Pressure Gauge

Since Im so kind here is a list for McMaster...

8063K38 - 1.93
4089K25 - 8.32
4429K251 - 4.36
4480K23 - 3.02 (2)
51165K11 - 1.55 (~5')
4880K58 - 7.45
4880K78 - 5.46
4880K614 - 7.22
4880K214 - 1.94 (2)
4882K15 - .75
Sprinkler Valve I dont feel like finding...
Cant Find the F-in Elbow things...
4880K76 - 1.10
Then the pipe that you should buy locally if you so choose to buy online, although I reccomend to buy locally.

Got lazy there at the end and am gonna crash out... Feel free others to complete and expound on my listings...

How much would the parts on the list you provided cost?

I think since I did you a EXTREMLY large favor by even providing a parts list, much less part numbers and prices, that you can simply look at those figures and add em' up. Of course your local hardware store will be cheaper so deduct something like 25%-50% of the figured McMaster cost. Thats going to give you a rough figure, seeing as I dont have the foggiest on the rates in you area. Me for example, I can proably get that list at 100% since I order my products from a supplier. So the prices will vary by location.

Sorry to bother you about the prices. I really appreciate the list, though. Thanks!

If anyone in the scene is around this when it fires off, make sure to sift the dirt, so that there are nor rocks in it that could hit someone, or rain down on the crew/equptment.

Sorry for the off topic question but does the thunderpipe actualy use a sprinkler valve to release, wouldent you be able to use it only under 125psi the sprinkler valve cant take much more can it, oh and its running on the solenoid it isnt even modded?

the thunderpipe only uses the sprinkler valve for a burst of air, the entire purpose of it is to make explosive effects, literally. It uses kerosene or something to make a huge fireball, it gets ignited and at the same time pushed by the air.