Introduction: Pneumatic Cannon

Brainstorming

I first came up with the idea for a pneumatic cannon after years of tinkering with different styles of combustion cannons. The concept of a pneumatic cannon was much more complex than that of a simple combustion cannon. Unlike combustion cannons that require a contained explosion to propel a projectile, a pneumatic cannon uses a controllable propellant that is compressed air. To construct the cannon, the first thing required was to come up with a design concept.

Step 1: Materials and Equiptment

Materials
  • 5' X 2" schedule 40 PVC pipe
  • 23.5'' X 4" schedule 40 PVC pipe
  • 2, 4" schedule 40 PVC caps
  • 2" schedule PVC cap
  • 2, 2'' to 4'' PVC Pipe Bracket
  • 1/2" ball valve
  • 4" X 1/2" copper tube
  • 2, 1/2" copper elbows
  • 1/2'' 100-150 psi gauge
  • 1/4'' 150 psi safety release valve
  • Schrader valve
  • Teflon Tape
  • 1/2'' to 1/4'' Copper reducer
  • 2, 1/2'' Male X 1/2'' Compression Adapter (Copper X Copper)

Price of Materials: $180.00-$190.00

Equipment
  • PVC Primer
  • PVC Cement
  • Blowtorch
  • Solder
  • Flux
  • Drill
  • 1/4" Hand Tap
  • 1" Hand Tap
  • Hacksaw
  • Step Down Drill Bit
  • Adjustable Wrench
  • Pipe Cutter
  • Pliers
Estimated Project Time

2 days

Step 2: Concept and Design

Barrel

The barrel of any cannon is used to store a projectile before launch and to guide it as it is being projected. The majority of my designed cannons use schedule (SCH) 40 PVC plumbing pipe. For my pneumatic cannon, I chose to use SCH 40 PVC pipe at a 2" diameter.

Chamber

The chamber of a combustion cannon houses a combustible fuel, such as diethyl ether (engine-starting fluid), that is ignited by a spark from an electrical source. For my combustion cannons, I use a grill igniter to create the spark. The chamber is directly behind the barrel and connects to the barrel by a PVC bell-coupling. In a pneumatic cannon, the chamber is vastly different. Whereas the chamber of a combustion cannon is located behind the barrel, my pneumatic cannon attaches the chamber next to the barrel in a parallel fashion. This pneumatic chamber does not use an accelerant to create a contained explosion, rather it contains pressurized air to launch the projectile.

Valve Assembly

My pneumatic cannon uses a 1/2" ball valve to release pressurized air from the chamber into the barrel, ultimately firing the cannon.

Step 3: Calculations

Equations
  • Volume of a Cylinder: V = πr^2h
  • Length of Chamber: h = V/πr^2
Finding Dimensions

The rule of thumb that i follow for all of my cannons is that the volume of the chamber should be no larger than 1.5x the volume of the barrel. The reason behind the 1,5x larger constraint is for the build up if gas/pressure to be to escape at a reasonable and safe rate. Since I decided to go with a 5' barrel I needed to find the volume and then use the barrel volume to find the volume of the chamber.

Step 4: Cutting the PVC to Length

Caution: When Using Hacksaw
Barrel
  1. Measure a length of 2'' SCH 40 PVC pipe to a length of 60'' (5').
  2. Proceed to cut the 2'' SCH 40 PVC pipe with the Hacksaw
Chamber
  1. Measure a length of 4'' SCH 40 PVC pipe to a length of 23.5''
  2. Proceed to cut the 4'' SCH 40 PVC pipe with the Hacksaw

Step 5: Capping the PVC

Caution: Fumes of PVC Cement and PVC Primer, Staining of PVC Primer
Barrel
  1. Use the PVCPrimer to clean and prepare both the cap and the barrel.
  2. Apply the PVCPrimer to outside of one end of the barrel, going about 3'' down from the end.
  3. Apply the PVCPrimer to the entire inside of the 2'' SCH 40 PVC cap
  4. Allow to dry: 5 minutes
  5. Apply a generous amount of PVC Cement to the stained area of the barrel where the PVC Primer was applied.
  6. Apply a lesser amount of PVC Cement to the area where the PVC Primer stained on the inside of the 2'' SCH 40 cap.
  7. Insert the end of the barrel with the PVC Cement into the 2'' SCH 40 cap.
  8. Allow to cure: 12-24 hours
Chamber
  1. Use the PVC Primer to clean and prepare both ends of the chamber and both 4'' SCH 40 PVC caps.
  2. Apply the PVC Primer to the outside of both ends of the chamber, going about 3'' down from the end.
  3. Apply the PVC Primer to the entire inside of both 4'' SCH 40 PVC caps.
  4. Allow to dry: 5 Minutes
  5. Apply a generous amount of PVC Cement to one end of the stained area of the chamber where the PVC Primer was applied.
  6. Apply a lesser amount of PVC Cement to the inside stained area of one of the 4'' SCH 40 PVC caps.
  7. Insert the end of the chamber with the PVC Cement into the 4'' SCH 40 PVC cap with the PVC Cement.
  8. Repeat for the opposite end of the chamber.
  9. Allow to cure 12-24 hours

Step 6: Tapping the Chamber and Barrel

Barrel
  1. Using the down step bit, drill a 7/16'' hole in the center of the 2'' SCH 40 PVC cap.
  2. Use the 1/2'' hand tap and tap the 7/16'' hole. (Be sure to tap the hole smoothly and straightly)
Chamber
  1. Using the the down step bit, drill a 7/16'' hole in the center of one 4'' SCH 40 PVC cap.
  2. Use the 1/2'' hand tap and tap the 7/16'' hole. (Be sure to tap the hole smoothly and straightly)
  3. On the opposite end of the chamber drill three holes. Using the down step bit, drill two 7/16'' holes and one 3/16'' hole. (Use picture for placement reference)
  4. Use the 1/2'' hand tap to tap the 7/16'' holes. (Be sure to tap the hole smoothly and straightly)
  5. Use the 1/4'' hand tap to tap the 3/16'' hole. (Be sure to tap the hole smoothly and straightly)

Step 7: Fitting Adapters and Gauges

Barrel
  1. Wrap the Teflon tape around the 1/2'' Compression fitting. (2-3 revolutions)
  2. Slowly turn the 1/2'' Compression fitting, using the adjustable wrench, into the tapped 1/2'' hole on the 2'' SCH 40 PVC cap until it does not turn anymore.
Chamber
  1. Wrap the Teflon tape around the other 1/2'' Compression fitting. (2-3 revolutions)
  2. Slowly turn the 1/2'' Compression fitting, using the adjustable wrench, into the tapped 1/2'' hole on the 4'' SCH 40 PVC cap until it does not turn anymore. (This fitting goes into the side of the chamber with just 1 hole)
  3. Wrap the Teflon tape around the 1/2'' 100-150psi Pressure Gauge. (2-3 revolutions)
  4. Slowly turn the 1/2'' 100-150psi Pressure Gauge, using the adjustable wrench, into one of the 1/2'' tapped holes on the side of the chamber with 3 holes until it does not turn anymore.
  5. Wrap the Teflon tape around the 1/2'' to 1/4'' Copper reducer. (2-3 revolutions)
  6. Slowly turn the 1/2'' to 1/4'' Copper reducer into the other 1/2'' tapped hole on the 4'' SCH 40 PVC cap, using the adjustable wrench, until it does not turn anymore.
  7. Wrap the Teflon tape around the 1/4'' 150psi Safety Release Valve. (2-3 revolutions)
  8. Slowly turn the 1/4'' 150psi Safety Release Valve, using the adjustable wrench, into the 1/2'' to 1/4'' Copper reducer until it does not turn anymore.
  9. Wrap the Teflon tape around the 1/4'' Schrader Valve. (2-3 revolutions)
  10. Slowly turn the 1/4'' Schrader Valve, using the adustable wrench, into the tapped 1/4'' hole until it does not turn anymore.

Step 8: Valve Assembly

Caution: When using Pipe Cutter and Blowtorch
  1. Using the Pipe Cutter, cut the 1/2'' X 4'' Copper tube into 1'' segments.
  2. Dry fit the Valve assembly together.
  3. Apply a generous amount of flux around a 1'' segment of 1/2'' Copper tube and heat with the Blowtorch until the flux melts.
  4. Apply a generous amount of flux to the inside of a 1/2'' Copper elbow and heat with the Blowtorch until the flux melts.
  5. Insert the side of the 1/2'' Copper tube with flux on it into the 1/2'' Copper elbow with flux on it.
  6. Heat the assembled piece with the Blowtorch until the 1/2'' Copper tube turns a greenish color, then apply the solder. (Ensure there is a complete seal between the 1/2'' Copper tube and 1/2'' Copper elbow)
  7. Repeat (6) for the other side of the 1/2'' Copper elbow with another segment of 1/2'' Copper tube. (Be sure to point the flame of the Blowtorch away from the previously soldered Copper tube)
  8. Repeat all for the other 1/2'' Copper elbow
  9. Allow to cool: 10 minutes
  10. Insert both of the partial assemblies into the 1/2'' Male X 1/2'' Compression fittings and tighten. (Be sure to align the partial assemblies so the 1/2'' Ball Valve will be straight.
  11. Apply a generous amount of flux to the 1/2'' Copper tube and heat with the Blowtorch until the flux melts.
  12. Insert the 1/2'' Copper tube one and of the 1/2'' Ball Valve. (Aligning the 1/2'' Ball Valve for a comfortable firing position)
  13. Heat the 1/2'' Copper tube until it turns a greenish color, then apply the solder. (Be sure to point the flame away from the 1/2'' Ball Valve and for a proper seal to be formed)
  14. Repeat (11-13) for the other side of the 1/2'' Ball Valve.
  15. Allow to cool: 10 minutes

Step 9: Securing the Barrel to the Chamber

  1. Using a 2'' to 4'' PVC pipe bracket, connect the Barrel to the chamber.
  2. Place 1 2'' to 4'' PVC pipe bracket near the valve assembly and the other near the opposite end of the chamber.

Step 10: Testing

Test for any air leaks, if leaks are present, you can apply a silicone sealant around the fittings and soldered areas. if there are no leaks present, proceed to having a Blast!

Comments

author
Zacslabon (author)2016-05-31

this is good

author
selias33 (author)2014-05-22

Nice job, AJ.

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