When heat is applied to a metal hydride container, the stored hydrogen is released from the alloy under pressure. The gas pressure pushes a piston, creating a powerful linear motion in a mechanical system. In the same way, when the container is cooled, the hydrogen reenters the metal hydride causing linear motion of the piston in the opposite direction. The pressure of the hydrogen gas is proportional to the metal hydride temperature, so precise positioning of a bellows or piston can be achieved by controlling the hydride temperature.
Hydride temperature sensor-actuators are suited for applications that require large force in response to changing temperature. For example, hydride actuators generate enough force to automatically open and/or close valves.
Ergenics has developed an on/off fire sprinkler that will reliably, repeatedly and quickly provide a large amount of water on a fire and will automatically turn off the water when the fire is extinguished. The sprinkler is based on metal hydride sensor/actuator technology. When the metal hydride coil is exposed to the heat of a fire, the gas pressure developed is used to open the water valve. The temperature of operation can be varied by alloy selection. The process is reversed as the hydrogen is re-absorbed by the cool hydride after the fire is extinguished. This greatly reduces the water damage typically caused by a conventional "one-shot" fire sprinklers. Because Ergenics' fire sprinkler turns the water off when the temperature drops, pressure in the water main is maintained and the sprinkler is ready to reactivate in case the fire rekindles.