Making Apparatus for Pressure Demonstrations

Four types of demo equipment are described in this page: (A) a sealed cover for the familiar "boil water in a soft drink can/cool/crush" demo; (B) a "throw balls" competition demo, (C) an expansion chamber for a better "crush the soft drink can" demo, and (D) an add-on to the expansion chamber to make it capable of launching paper rockets.



Materials/Equipment Required

A. Cap
2" PVC cap
3/8" thick self-adhesive weather stripping
Masking tape
1" x 8" strip of heavy cloth or rug.

B. Throw the Balls
20" x 30" foam board
coat hanger
two pairs of pliers (one should have a good wire cutter)
Pony beads
Scotch Extreme Tape
six 10' lengths of 3/4" PVC tubing (heavy wall)
16 PVC Tees, for 3/4" tubing
4 PVC couplings, for 3/4" tubing
PVC cutter (or saw and sandpaper)
50-100 Ball Pit balls (hollow, polyethylene, approximately 3" diameter)

C. Expansion Chamber
Glue gun (high heat)
PVC cement
1.25" fender washer
1.5" knockout sseal
2' length of 2" PVC pipe
2' length of 1.5" PVC pipe
6" length (approx) of 1.5" PVC pipe
1.5" PVC Tee
2" x 3" PVC pipe increaser
3/16" self-adhesive foam weather stripping
3/8" self-adhesive foam weather stripping

D. Addon
1' (approx.) 3/4" PVC pipe
1.5" x 3" PVC pipe increaser
1.5" x 3/4" PVC reducing flush bushing
tape (such as duct tape)


A1. In the familiar "boil water in a soft drink can/cool/crush" demo, the demonstrator grasps the can, inverts it, and quickly plunges it in to cool water. The can can ( and does) take in liquid water. The presence of this water can complicate the interpretation of the demonstration -- which is multi-concept anyway. The cap described here eliminates one concept/confusion.

The finished cap is shown at the upper left. To make it, a 2" PVC cap, adhesive backed weatherstripping, masking tape , and a piece of cloth/rug are needed (1" x 8" or so).

Work the weatherstripping into the outer edge of the PVC cap. Be sure to butt the ends togehter tightly so that therre is no air leak. Place the strip of rug across the sealed end of the PVC cap and tape it to the cap, as shown.

A2. To use, push the assembly down onto the soda can, and use the rug fingers to hold it onto the can -- with no burned fingers!.

B1. Some of the items you will need, and two roller support assemblies (one incomplete).

B2. Close up of one of the roller assemblies. You will need to start with a piece of coat hander wire approximately 8" long. There are 15 of the Pony Beads on the wire. Use trhe glue gun to glue the two outer beads to the coat hanger wire. Be sure to allow jsut enough room for the other beads to rotate freely.

B3. A bag of Pony Beads. I paid $1.97 for 500 beads..

B4. . Tape the two roller asemblies onto a 30" edge of the foam board. Use lots of tape -- the board takes quite a berating.. Look closely and you will see that there is tape on the foam board, and then the tape that goes through the roller assemblie tapes to the prior tape. The two roller assemblies should be 27" between centers..

B5 Cut four of the 10' lengths of PVC tubing in half, to result in eight 5' lengths. These are labeled "A". Cut the remaing 10' lengths into 2.5" lengths. Label four of these "B: and four "C". Cut two 1/5" lengths off of each "B" piece ("shorts").. You should be able to line up your pieces as shown in the image to the right..

B6. Start the assembly process. Fit tees onto the 5' pieces (A) to produce four sub-assemblies, as shown.

Until you are satisfied with the final assembly, fit the pieces together loosely. At the end you will force them together tightly to make a rigid assembly.

B7. . Use the remaining tees and the shorts to make the sub-assemblies show in the image at the right.

B8. Use the B pieces as cross supports, and make two rectangles. Use the four reaming A pieces to build up.


B9. Now put the top on -- you will need someone to help you.


B10 Open up the top -- carefully -- and put the poster board into the assembly.

The height is about 5', abouit right for elementary school kids.

B11. Use the couplings and the "C" pieces to extend the vertical suppoprts.

This about the right height for adults.

B12. Now it is ready. be sure to press all joints tight. Open up the ball bag, group the students into 4-5 person teams, and start the competition. The winning team is the one that drives the poster board into the other tema's end.

C1. This is a picture of the completed expansion chamber assembled and ready for use.
C2. This picture shows the chamber and the plunger.

C3. Here is what you will need to build the expansion chamber. Oops, I left out the 3/16" thick weatherstripping.

Use the PVC cement to glue the three pieces of the plunger together, as shown in C2. C6. Use PVC cement to glue the 2" x 3" pipe increaser to the 2" PVC tubing, as shown in C2. No leaks!

C4. Glue the washer onto the knockout seal. Use lots of glue. The washer reinforces the yellow plastic.

C5. Glue the knockout seal into the 1.5" PVC pipe. Use lots of glue, since there must be no leaks.

Put a strip of 3/16" weather stripping around the end of the 1.5" PVC pipe, about 1" from the end. Make sure that the butt ends press tightly together so that there will be no air leak at the junction.

Lubricate the outer side of the weather stripping with vaseline.

C6. Place the 3/8" weather stripping in the 2" x 3" pipe increaser, just at the edge of the conical section. Be sure to make the butt ends push tightly against each other to avoid leaks. The foam insulation must be squeezed to make it fit into the inner part of the cone.

C7. Push the plunger all the way in, place a can in the pipe increaser -- force the can down into the weather stripping to make a good seal.


C8. Pull back quickly on the plunger, and you have a crushed can.

WORRY: Suppose that a student decides to try to launch a can across the room by pushing the plunger in quickly -- this could be dangerous. However, because the weather stripping is in a conical support, the can will just pop out without any appreciable distance. Try it yourself.

D1. Launcher Addon. Here are the pieces.
D2. Press the pieces together -- no need to glue them.
D3. Use duct tape to attach the Addon to the 2" x 3" pipe increaser at the end of the expansion chamber. Put a paper tube rocket on the 3/4" PVC pipe, pus the plunger in rapidly, and the rocket goes.


(I have no financial interest in any of the suppliers mentioned.)

PVC stuff and weather stripping – any hardware store. I got mine at Home Depot.

Glue gun (high heat) and glue sticks (0.28” diameter, multi-heat). Pony Beads. Any crafts store. I got mine at Walmart.

Foam board - Office Max

If you are in a bind, contact Lynn Melton.




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