Here is the inside of an aluminium hot-air balloon tank. This ‘cut away’ clearly shows how a hot-air balloon cylinder works…

From the top.
You can see on this tank – the liquid valve which draws liquid fuel from the tube at base of the tank (silver handwheel valve) and the vapour valve (red wheel regulator valve) which could run the vapour pilot light on your burner if it had one, the pressure-relief-valve (PRV) is shown with the black plastic dust cap on it, the bleed valve used when filling the tank is the small screw valve and in the centre, the dial for the float gauge indicates the amount of liquid fuel in the tank.

Inside.
You can see the kinked ‘dip tube’, the contents float gauge, the bleed valve tube at a high fixed level to indicate when to stop filling as your tank is full enough and the pressure relief valve.

Important notes – Not all tanks have a kinked dip tube and cylinders can have different valve configurations.

Source: cameronballoons.co.uk