1. Field of the Invention
The inventions disclosed and taught herein relate generally to solenoid valves; and more specifically relate to thermal protection of solenoid valves operating in hazardous environments.
2. Description of the Related Art
U.S. Pat. No. 3,839,692 discloses “a thermal limiter construction which can be used to limit one or more electrical circuits and comprises a thermally responsive device having leads for being interconnected into such electrical circuit or circuits and a plurality of electrically operated heaters disposed adjacent the device and each being adapted to cause the device to open the circuit or circuits when heated by the respective heater a certain amount.”
U.S. Pat. No. 4,227,169 discloses a “device [that] will open an electrical circuit in response to either an increase in ambient temperature or an increase in electrical current. A bracket is provided to support a radial lead thermal cut-off device. The bracket is of a general C-shaped configuration and has an extending lead bar that is crimped into electrical engagement with an input lead, and one radial lead of the thermal cut-off device is crimped into electrical engagement with the second input lead. A helical conductive coil has one end welded or otherwise secured to the C-shaped bracket, and the second lead of the thermal cut-off device is crimped to the other end of the helical coil which is positioned over the thermal cut-off device so as to surround it. Thus, an ambient temperature rise may cause the thermal cut-off device to open the electrical circuit; or alternately the heat generated by the I.sup.2 R loss in the coil due to excessive electrical current flow may cause the device to also open.”
U.S. Pat. No. 4,808,960 discloses a “thermal cutoff having a metal foil resistance heater circuit bonded to its outer surface.”
U.S. Pat. No. 4,821,010 discloses a “thermal cutoff includes a housing having a resistive coating bonded thereto, and defining a heater for heating the thermal cutoff to its firing temperature.”
U.S. Pat. No. 4,968,962 discloses a “thermal cutoff and a heating resistor are assembled in heat transfer relationship with one another by a metal clip. The assembly is mounted on a base of dielectric material. Electric leads on the thermal cutoff and resistor extend through holes in the base for connection to a printed circuit board.”
U.S. Pat. No. 5,304,974 discloses a “thermal cut-off resistor that has an elongated thermal cut-off fuse; a wire-shaped resistor that is tightly coiled around the fuse, said resistor being physically connected to the fuse so that the fuse and the resistor are in an electrical series arrangement; and an electrically-insulated heat-resistant casing that contains the fuse and resistor therein and enables the fuse and the resistor to be secured and electrically connected to respective electrical contacts formed on a printed circuit board, the profile of the casing being approximately the width of the fuse.”
The inventions disclosed and taught herein are directed to an improved system for thermal protection.