AWBRL for short. Just the other day I was watching a mythbusters episode where they made water bottle rocket launchers for a myth. It looked like so much fun and I went ahead and bought an aquapod for $35. It was great until it ruptured under normal use and no modifications! After that, I went to my local hardware store and bought a bunch of PVC fittings and a few other things so I could make my own with better reliability. This Instructable is about how to make a reliable, high performance, water bottle rocket launcher for cheap!
Lets make It!

Step 1: Safety

Now here is the important part. The safety information.
This is a pressure vessel. Pressure is dangerous. This bottle rocket launcher will utilize pressures up to 60psi. If you want to, you can add a safety valve but it would be easier to regulate the pressure with the source of air pressure. In my case, my portable air compressor.
Make sure you use pressure rated PVC pipe. sch40 is recommended but I used another type rated to 260psi
As with any pressure vessel, be cautious around it at all times.
ALL components MUST be pressure rated.
BE SAFE!
Do not use pressures over 60psi. There is no need. No increased performance at all!

Step 2: Parts

The total cost, without the cost of the schrader valve, was $25 and the Aquapod costed $35 and it offers far better peformance!
Here is the list of the parts:
8x 10cm 15mm PVC pipes
20cm 15mm PVC pipe
3x 15mm 90 degree Elbow fittings
3x 15mm "T" fittings
15mm to 25mm coupler
4x 15mm PVC end caps
1 hose barb to threaded fitting.
1m (25 inches) of air compressor tubing
1x schrader valve (from bike tire)
2x hose clamps
10m of cord
15cm of thick wire
"O" ring to fit over the pipe

Step 3: Assemble Without Gluing

Simple. Just follow the picture and assemble it according to the picture. At the top of the 20cm piece of PVC, file a groove about 5cm down from the top. To make sure of a tight seal, use a water bottle to test. It should be reasonably tight and it should take a firm tug to pull it of. You should have a gut feeling when you get it right. Don't over file it!
Trill 5mm holes at the top of the 15mm to 25mm coupler. Put a small screwdriver through the holes once a water bottle has been "loaded". The way that the launch mechanism works is that it stops the bottle from leaving the launcher by putting a pin through the holes over the little "lip" that the bottle has. When the unit is pressurised, the pin is pulled and the rocket launches!

Step 4: Start Gluing

Now it's time to start gluing the components just as you built them in the previous step. Simple. Make sure you glue the 15mm to 25mm coupler or it wont work very well.

Step 5: Finishing Up Construction

AFTER YOU HAVE WAITED 24 HOURS:
Drill the hole and thread in the hose barb for fitting. I used liquid nails around the threads to keep it from coming out at pressure and to ensure a good, tight seal. I used hose clamps to keep the hose barb fitting connected to the tubing and on the other end, the salvaged bike tyre valve, also with a hose clamp.
If you want to, you can use some waterproof spray paint and paint it. That is going to be the next thing on my to do list.

Step 6: Results and Math

At 50psi, here are the results:

The rocket flew 1m in 1 frame.
In the video, there were 30 frames a second
That resulted in 30m/s
Convert that to feet/second and it's 98.5 f/s
That equals 67 miles/hour
That then equals 108km/h and that is fast.
If the rocket went 30m into the air, as specified as the maximum height reached by the aquapod, the rocket had a flight time of 1 second and by my timing, 3 seconds falling back down to earth
That velocity equals approximately 92 joules of energy which then equals, correct me if I'm wrong, 92w