Personally I find splicing too much trouble. It involves glue, and I am not friends with glue... any glue... I usually get results like this:
So for me the staging system (stager) needed to fit on a Robinson Coupling. A Robinson Coupling is a connection between the bottom of a rocket and a cap. Thus making it possible to connect bottles top to bottom. I use the idea that is explained here.
Incidentally If you would grab a Gardena coupling for the garden hose you can screw that right on the lamprod and with epoxy glue make an airtight seal!
This means I would like to have a stager that has a Gardena nozzle on one side. The Gardena coupling described by George without the spring would have to sit on top of that.
So I got one of these:
Cut off half of that. And got some silicone aquarium tube. I got a part from the bicycle valve and stuck that into the cut off Gardena nozzle, again with epoxy glue.
Below you see the metal ring inside the cut off nozzle.
The silicone tube comes through, a piece of plastic from the tip of the pen goes into the tube and makes it thicker. This way the tube is not able to pop out of the back side of the Gardena part.
From left to right:
Gardena coupling (no spring inside), bicycle valve, rubber sealingring, washer with small hole, silicone tube in the middle, Gardena nozzle with ring inside, pen tip, sealing ring for the Gardena coupling.
Closeup of the valve, the airinlet goes into the silicone tube, that goes into the rubber washer, and into the metal washer. Using the sealingring one can connect this part onto the Gardena coupling.
The sealing ring is used to screw the whole thing to the modified Gardena coupling. The coupling has no spring, and I took off the hooks that hold the garden hose and the part that sticks in the garden hose. The sealing ring pushes the metal ring into the rubber ring which in turn seals the tube on the coupling:
Here is the assembly:
Almost done! I need a sleeve to put this in:
This is standard PVC pipe for the sink. A Gardena coupling goes in and is really tight!
I got a plastic holder from the inside of a medical tape ring and , cut that to fit in the bottom Gardena coupling. That prevents the coupling from accidently opening.
This one is loaded with a 1.5 liter bottle which is half full of water! It holds down the internal tube of the Gardena coupling and thus holds the bottle tight.
The Silicone tube has quite a lot of spring to it. It is so much that it pushes the inside of the top Gardena coupling out (since that has no spring inside). You can see this in the following YouTube movie. In the end I put in one Gardena spring, just to make sure the thing does actually pop open. George Katz mentioned that he had trouble with that at first:
So how did it go? The whole thing was too heavy I think. Next time, smaller stages and lighter too! I put in 7 bar. First stage was 3,5 liter , 1,25 liter water, second stage was 2,5 liter, 0,9 liter water. Tomy timer, camera, etc. all aboard.
Here is the launch. It was kinda funny!