FAQ's

Frequently asked questions compiled with technical data and specifations that will help you construct the best cannon you can posssibly build.

 
 
 

Frequently Asked Questions

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  1. How do I know what size pipe to buy?
  2. Where can I find information on pressure?
  3. Why doesn't my combustion cannon fire the first time?
  4. Where can I find more information on Spud Guns?
  5. Where can I find more information on PVC?

How do I know what size pipe to buy?

Good question!  You have a ball that you want to shoot out of the gun but which pipe will I need?  r> Measure the ball and find the pipe that is just slightly larger than the ball - or slightly smaller if the ball
has a little give to it.  You want a snug fit but you don't want to have to force the ball into the barrel - after
all we don't want to make a pipe bomb, we just want to launch a ball.  Look at the chart below for PVC
pipe size information.  Lets say you have a ball that measures 1.5" diameter.  Using the chart below you
can see that the best fit for this ball would be 1-1/2" schedule 40 pipe.  The inside diameter is just slightly
larger than the ball.

  Schedule 40
PVC
Schedule 80
PVC

Diameter

(inches)

O.D.

(inches)

Wall
Thickness

I.D.

 

Pressure
73°F
(psi)

Wall
Thickness
(inches)

I.D.

Pressure
73°F
(psi)

1/2

.840

.109

.602

600

.147

.526

850

3/4

1.050

.113

.804

480

.154

.722

690

1

1.315

.133

1.029

450

.179

.936

630

1 1/4

1.660

.141

1.360

370

.191

1.255

520

1 1/2

1.900

.145

1.590

330

.200

1.476

470

2

2.375

.154

2.047

280

.218

1.913

400

2 1/2

2.875

.203

2.445

300

.276

2.290

420

3

3.500

.216

3.042

260

.300

2.864

370

4

4.500

.237

3.998

220

.337

3.786

320

6

6.625

.280

6.031

180

.432

5.709

280

8

8.625

.322

7.941

160

.500

7.565

250

10

10.750

.365

9.976

140

.593

9.493

230

12

12.750

.406

11.888

130

.687

11.294

230

14

14.000

.438

13.072

130

.750

12.412

220

16

16.000

.500

14.936

130

.843

14.224

220

18

18.000

.562

16.809

130

.937

16.014

220

20

20.000

.593

18.743

120

1.031

17.814

220

24

24.000

.687

22.544

120

1.218

21.418

210

 

PVC Schedule 40 and 80 pipe is marked as prescribed in ASTM D-1785 to indicate the manufacturer's
name or trademark, material designation code, the nominal pipe size, the Schedule size with the
pressure rating in PSI for water at 73ºF, the ASTM designation number D-1785 and the NSF seal for
potable water.

 

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Where can I find information on pressure?

When constructing pneumatic spud guns it is important to know the pressure ratings of the pipe you are
using.  To maintain a safe environment always install a pop-off regulator that will release excess pressure
when the rated pressure in the gun has exceeded the maximum operating pressure.

PVC and CPVC Pipes
Nominal Pipe Size
(inches)
Required Minimum Burst Pressure
(psi)
Maximum Operating Pressure
(psi)
Schedule 401) Schedule 802) Schedule 40 Schedule 80
1/2 1910 2720 358 509
3/4 1540 2200 289 413
1 1440 2020 270 378
1 1/4 1180 1660 221 312
1 1/2 1060 1510 198 282
2 890 1290 166 243
2 1/2 870 1360 182 255
3 840 1200 158 225
4 710 1110 133 194
5 620 1040 117 173
6 560 930 106 167
8 500 890 93 148
10 450 790 84 140
12 450 600 79 137

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Why doesn't my combustion cannon fire the first time?

Well, as most ballistic professionals will tell you, you have to have a propellant. That is the easy part, as
most propellants come in the form of aerosols such as Axe Body Spray, Right Guard deodorant, Aqua
Net hairspray, starter fluid, and the list goes on and on. What most people don’t know is that in order to
fire, the fuel also needs oxygen. A common assumption is that the more aerosol you spray in to the
chamber the farther the ammo will go. This is not the case. You also need the correct amount of oxygen
in the chamber at the correct ratio with any form of propellant other then compressed air. Think about it.
How does a gas power engine work? How does a gun, for that matter, fire? You need the correct amount
of oxygen coupled with gunpowder to fire the gun. Fire needs oxygen.

Try this, spray less aerosol propellant into the chamber. If that does not work, after spraying the aerosol
into the chamber, blow into the chamber for about three seconds before capping. This should maximize
your range and efficiency. Remember, you need the correct fuel to oxygen ratio when firing your
combustion cannon. If more power is what you are after, then try a bigger chamber that will allow for a
greater ratio.

If you are having trouble with the second or third time you fire your cannon, then you have a “gas problem”
Yes, that’s right, you have a “gas problem” that Tums or Rolaids cannot fix. Gas it what propels your
ammo through the air, and is created when the fuel and oxygen are ignited. Try blowing into the chamber
to clear the remaining gases trapped inside your cannon. You may want to think about a small fan that
runs on batteries that is mounted inside your chamber. However, I’ll save that for another time.

If you have tried all of these helpful hints and your gun still does not work, email us on the Contact Us
section of the site with specific details of what you are doing and what your gun’s symptoms are. We will
be glad to offer any insight to your specific issues. Who knows, we may even post your problem, and our
answer on our site.

Some Helpful Questions regarding your Sparker from "Spud Talk"

Do you know of a way to make some assembly procedures easier?  How about how to make a better sparker.  This is the place to share and ask specific questions on design, assembly and use of all types of spud guns.

capt. potatoe // April 1, 2008 at 5:51 pm

I have the same question. a few bags of spuds ago I built my first spud launcher. Combustion model with spark plug in the chamber with grill igniter on the trigger. Inject hairspray the cheaper the better $1.99 can) close up the back, press the trigger. Sometimes first time but a lot of the times many pushes of the button before it’ll fire. Anybody got any feed back? I have a photo of the assembled unit if anybody’s interested.
  • Extreme Spud Master // April 1, 2008 at 7:01 pm

    Well, Two Things about hairspray. One, it will gum up the igniter. When the fuel in the spray burns off, then the igniter and the inside of your cannon, as well as, the twist cap is left to deal with the sticky residue. Ugh! A fix to this problem is that most aerosols are lighter than air. So by positioning you sparker at the top of the cannon will make for an 75-77 percent sparking to ignition ratio. that is if you clean it every time. I have no problems with mine. and I will explain in step Two. My igniter is positioned on the bottom. What, I just said to position it on the top? Well, that is because I use right guard deodorant. This fuel is heavier than air. You will find that you ratio is much higher. I hope this helps. If you do not want to spend the time with fixing the position of your igniter then switching fuels is recommended. Before you do that, use warm water and soak the interior of your cannon to get rid of the gunky build up. Spray Starch is an option. So is bug spray, however, that gives off toxic fumes and is not conducive to firing in doors. Just kidding regarding firing in doors.

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Where can I find more information on Spud Guns?

“You can find alternative methods to fire a potato, such as, hybrid cannons and piston cannons at www.spudfiles.com.“

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Where can I find more information on PVC?

Common Terms of Plastics

 “Originally posted by Drac on the Spudtech forum and modified by”…Sqort87 from
  LaunchPotatoes


Helpful Terms:

NSF-PW: means that the pipe is pressure rated. (PW=Potable Water)

XXX PSI: the pressure the pipe is rated to.

DWV: Drain, Waste and Vent: safe for Combustions, not for pneumatics.


Male NPT x Socket Weld: Adapter with male threads that fits over a pipe by slipping on.


Female NPT X Socket Weld: Adapter with female threads that fits over a pipe by slipping on.


NPT x Spigot: fits into a coupling, Tee, Adapter, or anything that joins over pipe. Spigot fittings
          have the same outer diameter as the corresponding pipe.


PVC: Polyvinyl Chloride: Standard pipe, pressure rated but can become brittle in the cold.


ABS: Acrylonitrile-Butadiene-Styrene: fine for combustions, but not pressure rated so DON'T USE
        IN PNEUMATICS!


Cellular Core: Very Unsafe. I wouldn't recommend to use it in anything.”

 

To get some more helpful hints regarding plastics used in the construction of
combustion or pneumatic cannons click on the link below. This is great stuff.
You will not regret it.

http://www.launchpotatoes.com/forums/viewtopic.php?t=34

 

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