My brother teaches Science at his Elementary School, and for the past month I've been helping my brother make Water Bottle Rockets. The problem we are having is the lost of pressure from the launch tube. Like to maintain 125 PSI for 24 hours.

We tried the rubber stopper which works well, but the release mechanism is flaky. We are now using what is referred to as the "Ian Clark Cable Tie Release" with an o-ring.

To achieve this we need to use a 1/2" PVC with an o-ring. We tried to lave (did this with a drill, by adding a screw to a cap and use a filer) out a grove but that grove weekend the PVC. In our research, we found a site that used a 1/2" CPVC Pipe as a coupler that slide inside the 1/2" PVC. This sounds perfect but the O.D. 1/2" PVC is way to small. BTW: Trying to get CPVC in Southern California is a very difficult task.

The launch tube is made of standard 1/2" PVC. It has an O.D. of 0.840 per the manufacturer (approximately between 13/16" and 7/8"). The I.D. is approximately 23/32" or 0.719 from what I can measure. The 1/2" CPVC has the same O.D. as a 1/2" Copper Pipe of 5/8".

The only material that both my brother and I have found, that slides snug inside the 1/2" PVC is a 1/2" EMT Conduit and a 1/2" Copper Coupler where they both have an O.D. of 0.706 which is greater than 11/16" but less than 23/32". This is exactly what we need, but in PVC or CPVC or some other hard plastic.

Three questions:
1) Is there such a plastic material with an O.D. that is greater than 11/16" but less than 23/32"?

2) Should we glue PVC to copper or PVC to conduit?

3) Will liquid nail adhere to these types of material?

Sounds interesting. Try it and see.