Connectors

There are two types of connector cnsidered here: one made from a Woods/Schrader adaptor that you can get from a bicycle stockists; and the other from a Tyre Valve that you can get from any car tyre fitters workshop.

Woods/Shrader adaptorWoods/Scrader

This is a small brass adaptor (right) that comes with two one way valves in a kit. It is useful because one end of the inside is tapped so that you can screw the one-way valve in or have it as a nozzle.

 

Tyre Valve - you can get them from a tyre fitter's workshopTyre Valve

The Tyre Valve (right) is probably the most globally available option.

Valve AssemblyThe inner valve assembly (left) can be unscrewed, leaving a straight-through nozzle although it is smaller in diameter than the hole down the centre of the Woods/Schrader. This option does, however, produce a better connector for pressurising bottles for heat moulding.

 
To make the connector, (ie, with the one way valve) you will need to add the valve one the adaptor assembly you are making is in place.   To make the nozzle, you will need to remove the valve assembly from teh tyre valve before you put it in place.
Connector/Nozzle

The connector/nozzle is a dual purpose device that exists in two forms: a straight-through nozzle and a valved adaptor.

The former allows the rocket to be launched and enough thrust is developed to lift smaller rockets and the latter (making use of the valve) allows you to presurise a bottle and then disconnect the bottle from the air supply so that you can modify its shape carefully using heat.

The nozzle is made from the bottle top and a Woods/Shrader adaptor, sealed with a bit of Blu-Tack (one of these sticky gunge things that you use for sticking posters to walls and so on).   The nozzle is made from the bottle top and a Tyre Valve assembly. You will have to remove the one-way valve to allow water to flow through it.
 
To make the connector, make a central hole in the bottle top (the little pimple in the centre of the top - an artefact of the injection moulding process - shows you where the dead centre is) such that the external thread on the adaptor will screw into it (the diameter of this hole needs to be a little less than the outside dianeter of the thread - a tight fit is better than a loose one) roughly 7 mm. It is reasonably important that the hole is central and runs perpendicular to the surface of the bottle top - that is it should run axially to the bottle in order to provide a well directed jet of water. How you will make this hole depends upon what you have access to. . .   To make the connector, make a central hole in the bottle top (the little pimple in the centre of the top - an artefact of the injection moulding process - shows you where the dead centre is) such that the gap between the hemispherical end and the rest of the assembly will fit through the hole you are making. How you will make this hole depends upon what you have access to. . .
 
A sharp kitchen knife (such as a vegetable peeler) or a penknife may be used and will cut a good enough hole as will using a sharp drill (remember that the bottle top is soft) and finishing off the hole using a taper-reamer. It may take a few tries at this - I found that a sharp knife was good at slicing through towards one side.
 

Make a ring of Blu-Tack (or one of those plumbing sealant compounds - you need less than a gramme) and put it around the hole on the inside of the top and then screw the adaptor (right) into the hole in the top (as per the diagram above) so that the Blu-Tack (or whatever you used) forms a seal. If you used a flexible sealing compound that sets, now is the time to let it set but first, you need to make sure that the bottle can screw onto the cap and still leave a gap between it and the sealant.

You will probably find that a finger and thumb don't provide a good enough grip on the adaptor to tap the hole the first time that you screw it in. You can solve this either; by tapping the hole from the outside (where you will have a good enough grip), unscrewing the adaptor and then screwing it in again from the inside; or, by using a pair of pliers. Whatever you do, make sure that the adaptor goes in as straight as it can. Any deviation from axial will make the rocket fly in a loop.

  Simply push the tyre valve into the hole and it is ready to use.
     
If the top has a separate seal, cut a hole in that so that it will fit into the cap.

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