The event went very well. I hope to get a copy of a video recording made during the demonstration in the field outside the school. Meanwhile here are some notes on the cable-tie launcher I made for the school to use in their water rocket workshop later this year.
The pipework is constructed from John Guest JG Speedfit push-fit fittings in white PVC. Speedfit is a system of UK plumbing fittings that do not require glue, and which can be assembled and disassembled very quickly.
From left to right, the part description and reference number:
- 15mm appliance tap [15APT]
short length 15mm pipe
15mm-15mm-22mm reducing tee [PEM3022CW]
short length 15mm pipe
15mm-22mm reducing straight coupler [PEM202215W]
short length 22mm pipe
22mm stop end [PSE4622W]
- 3m x 15mm speedfit speedpex barrier pipe [15BPEX-20X3L]
3m x 22mm speedfit speedpex barrier pipe [22BPEX-20X3L]
4 x 15mm superseal pipe inserts [STS15]
3 x 22mm superseal pipe inserts [STS22]
3m was the minimum order length for white pipe; could have got shorter lengths of PEX pipe in dark gray: 2m lengths
dark gray fittings were cheaper but not always available in all fittings
could have saved by omitting the reducing straight coupler (if I had figured out the naming convention sooner) by using an asymmetric reducing tee, 15mm-22mm-22mm [PEM3022DW]
I built most of it in one session. Took about 15 minutes to assemble the pipework excluding the stop end and launch tube, most of which was cleaning up the cut ends of the pipes. About an hour in total getting the launch tube reduced from 22mm down to 21.5mm to fit snugly inside a bottle spout, and about 20 minutes drilling out the stop end and forcing the tyre valve into it. Another half an hour making up the cable tie, sleeve and sleeve spring. A half hour or so spent hacking together a stable support for the pipework.
When I came to do the water rocket demonstration I found that I'd forgotten to pack my original launcher that I had planned to use. So I ended up using the school one, and it worked perfectly... oh, except for one failure to launch, when I forced a rocket too far onto the launch tube and it would not release (even at 8 BAR). A good opportunity to demonstrate the pressure release tap!