I have received some private messages asking me to explain the cycle pump set up in a little more detail. For those interested it is really very simple:

2 bulkhead fittings in the cap of the fuel jug. Fitting A terminates just inside the cap and connects into the vapour space above the fuel level in the jug. Fitting B connects to a clunk line running to the bottom of the jug.

The air delivery line from the cycle tire pump connects via a non return valve (NRV) to fitting A – I have used a YS NRV for convenience and because I know that the internal disc will stand up to high nitro fuel. (In practice it only comes into contact with fuel vapour). Fitting B is connected to a short length of fuel tubing in which I have included a small clip that can be used to isolate the line while the fuel jug is being pressurised and after the tank in the model has been filled.

A few strokes of the cycle pump are enough to pressurise the fuel jug. When the jug is full, about 5 or 6 strokes will do the trick, depending on the swept volume of the cycle pump. It will take a few more strokes as the jug becomes empty because of the larger volume of vapour space above the fuel. Once the jug is pressurised, connect the fill line from the jug to the fill line on the model. Open the clip in the delivery line from the jug and sit back and wait for the tank to fill.

The burst pressure of fuel jugs is well above the pressure needed to “blow” fuel from the jug into the tank. However, as a precaution, I depressurise the jug after the tank in the model is full. The application of common sense should tell users if too much pressure is being applied, as the shape of the fuel jug will become excessively distorted. If you feel you can’t rely on common sense, fit a small relief valve to the jug!

The same set up can be used in reverse to pressurise the tank in the model and drain any fuel back into the jug. No moving parts come into contact with liquid fuel and I have used the system successfully with both gasoline and nitrated methanol.

AA