Hi folks who want to make own automatic boiler water level control system with phototransistor. The control unit is registering the level of water using phototransistor + red led mounted on the water level glass tube. The servo is used to open / close the bypass valve between the boiler and waterpump operated by steam engine or open / close the steam valve to feed pump driven by steam pressure such like as Stuart feeding pump or Southworth feeding pump or as you created own feeding pump. Pump time can be adjusted as required by the phototransistor have registered lowest water level and pump on to it is higher than the phototransistor. The purpose is that it should not be often to pump water into the boiler. Light sensitivity is regulated depending on the size glass diameter and thickness as the receiving signal when the water is inside the water level glass tube. The yellow led = low water/zero water level The green led = normal water level Both yellow and green led = water is pumping into the steam boiler The yellow led is off and the green led is on = pumping time is ended when the water level is in normal position. I did no want to drill hole in the boiler for water sensor since i has water level glass tube mounted on boiler. Hence i created the automatic boiler water level control system with phototransistor on glass tube. Here is the diagram of the automatic boiler water level system with phototransistor.