Backpack Water Cannon - 8 Litre

Step 2 Making the firing mechanism

First we are going to solder the connections to avoid damaging the other bits with the heat. This is fairly simple but you will need:

• Solder
• Soldering flux (everflux is highly recommended)
• A Blowtorch
• Silicone sealant (preferrably heat resistant) / Heat resistant epoxy.

Making a good solder joint is covered here and here, so you have no excuse to get it wrong.
You will want to solder the fittings so that the pipes will emerge parallel like in the photo.

Measuring and cutting to size

• I simply made the firing assembly to dimensions which were comfortable to hold (10cm and 30cm).
• Cut the pipe down slightly larger than you need (to allow for mistakes and what fits into the endfeed sockets), deburr and fit it all together (minus ball valves) as it will be when it is soldered. This is a great opportunity to check how the gun feels.
• To make space for the first ball valve you need to cut the 30cm section so that there is a piece long enough to fit in the tee and into the ball valve.
• Next up you need to attach this piece and the longer piece to your ball valve. At this point you can cut the long bit down to the size you want, so that it is the same length as the other piece you have.

Filling in the conection

• I used heat resistant silicone sealer (otherwise it could be damaged by the soldering later on). Alternatively, you could epoxy something in place to block the tube, such as a 20mm bearing or 12g CO2 capsule.
• Fill the entire piece of pipe wil the sealant, then excavate a few centimetres at each and place something to stop it flowing into these few centimetres.
• Use anything which is very close to 20mm diameter, because what runs down might burn when you solder the pipe later.
• When the sealant has cured enough to not flow, remove the plugs and leave it to cure completely.

Soldering the assembly

• You need to make sure it's completely flat, or it won't fit together properly.
• Follow the order in the picture. Solder everything so that it is connected to only one tee, then connect 2 tees.
• While the joint is still hot, push down the joint onto a flat surface. This will make sure that the 2 pipes are totally paralell.
• Do the same for the remaining pair of tees. If done correctly, they should fit together perfectly, if not, you can always heat them up again and rotate.