A real break through was made with the construction of a gasometer. Prior to this, various demand valves were tried, but without success. Given that the vapour pressure of propane is about 100psi at 15degC, it’s not really surprising that a demand valve would struggle to deliver reliably at a pressure of a few inches of water.
The gasometer supplies gas at a pressure of about 1” of water and interestingly, gives a visual indication of each induction stroke as seen by the slight drop of the float. The main water container is a plastic dustbin and a wooden frame supports the float, pipes and micro switches. The float is made from a plastic oil drum, with the top cut off. The main gas feed pipe is made from 22mm copper plumbing. When the float is at its lowest point, a plate on the float spindle operates a micro switch which powers the solenoid valve allowing gas to fill the float. When the float reaches its highest point, another micro switch removes power from the valve to halt the gas supply. A relay supplies the latching action.