McDonnell & Miller flow switches control the flow of liquids or air in pipelines to heating systems. Flow switches start or stop electrically operated equipment such as signal lights, alarms, motors, automatic burners, metering devices, and others. Many can be equipped with a time delay relay. McDonnell & Miller offers liquid flow switches and air flow switches for general purpose and high sensitivity needs, as well as, industrial applications.

McDonnell & Miller offers liquid level controls for applications such as cooling towers, storage tanks, water fountains, condensate receivers, and more. These liquid level controls provide an air pressure signal proportional to the liquid level and are designed for use with a remotely mounted controller to allow sophisticated multi-level control in tanks, boilers and hydronic systems. They can be used to activate a low level alarm, high level alarm, pump to fill/drain a tank or any combination thereof.

McDonnell & Miller low water cut-offs provide a reliable method of controlling a boiler feed pump. They are mounted at the boiler water line and starts and stops the pump as the boiler water dictates. Consequently, it holds the boiler water level at the limits recommended by the boiler manufacturer to maintain maximum steaming efficiency. McDonnell & Miller low water cut-offs are available in float-operated or probe and float built-in styles. McDonnell & Miller pump controls are available in or commercial and industrial low or high pressure boiler applications. McDonnell & Miller offers float-operated pump controllers with snap action switches for high temperature service, as well as, single pole, single throw switches and single pole, double throw switches for low water. Pump controls help maintain consistent water regardless of pressure. Some models feature magnetic repulsion operation, which eliminates the need for a bellows assembly, ensuring dependable operation at the higher pressures encountered.

McDonnell & Miller offers time delay relay switches for use with liquid flow and air flow switches, as well as, low water cut-offs. These switches permit intermittent switching of controlled equipment and eliminate false signals and rapid cycling from turbulence or fluctuations. They can be remotely mounted on main control panels or conduit boxes.

McDonnell & Miller offers valves for low water cut-offs, liquid level controls, water feeders, and flow switches. The type of valves McDonnell & Miller has available includes electronic probes, blow down valves, complete valves with strainers, and valve assemblies.

McDonnell & Miller water feeders open if the boiler's water line drops to the feeder or cut-off combination's feeder operating point, which is near the bottom of the gauge glass, the feeder will then open mechanically and add water to the boiler. How much water will enter the boilers depends on several things, but there will always be enough to keep the boiler operating at a safe minimum water level. Once it has added the right amount of water, the feeder closes.

State Supply offers a large inventory of McDonnell & Miller repair parts, for low water cut-offs, liquid level controls, water feeders, and flow switches. Some of the repair parts available include electronic probes, floats, gaskets, valves, o-rings, cartridges, and float rods.