Electricity: circuit makers and breakers – Fluid pressure – Diaphragm
Reexamination Certificate
2002-05-17
2003-07-22
Easthom, Karl D. (Department: 2832)
Electricity: circuit makers and breakers
Fluid pressure
Diaphragm
C200S0830SA
Reexamination Certificate
active
06596951
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention generally relates to pressure sensitive electrical switching devices and, more particularly, to pressure switches employing snap discs that change shape due to a snapping action caused by pressure applied thereto.
Pressure switches are widely used for controlling electrically operated devices by switching an electrical contact between open and closed circuit positions based on a preset fluid pressure threshold. For example, pressure switches are installed in fluid communication with the outlet side of a water pump in a heated spa/hot tub to monitor the water pressure. If the water pressure drops below a preset pressure threshold, such as may occur due to a potential water pump failure, the pressure switch changes state to disable power to an electrical heater to prevent further heating. Pressure switches are also employed in the exhaust passage of heating systems to shut off a furnace when the exhaust pressure drops below a preset pressure threshold. In addition to sensing positive pressure differentials, snap disc pressure switches could be configured to be responsive to negative pressure differentials, such as to operate as a vacuum switch.
Snap disc pressure switches typically employ a snap disc disposed in a fluid housing such that the snap disc is sensitive to the pressure of a fluid. The snap disc has a convex surface that changes shape to an inverted configuration due to a snap action when the applied fluid pressure reaches a preset pressure threshold. Many conventional snap disc pressure switches also include a movable connecting member and a movable contact arm engaged with the snap disc such that when the snap disc changes configurations between first and second shapes, the movable contact is moved between open and closed contact positions.
While some commercially available snap discs offer high reliability, upwards of several million cycles, prior known pressure switches utilizing snap discs are generally configured with several moving components, including a pressure-to-force converter, a movable contact arm, and a connecting member coupled between the snap disc and the contact arm. The presence of several moving components and the extended travel of such components increases the susceptibility of a component failure and increases complexity of the assembly of the pressure switch. Additionally, many prior known pressure switches are not easily adjustable to select the pressure threshold set point.
Accordingly, it is therefore desirable to provide for a snap disc pressure switch that offers high reliability, is easy to assembly, and is cost affordable. It is also desirable to provide a snap disc pressure switch that has minimal moving components. It is further desirable to provide a snap disc pressure switch that is easily adjustable to set the pressure set point at which the switch changes state.
SUMMARY OF THE INVENTION
In accordance with the teachings of the present invention, a pressure switch is provided for opening and closing an electrical connection based on a pressure set point. According to one aspect of the present invention, the pressure switch includes a housing comprising walls defining a fluid chamber adapted to receive a fluid. The pressure switch also includes a snap disc having a front surface in pressure communication with the fluid chamber and responsive to switching states between first and second shapes based on a pressure set point, and an electrically conductive rear surface. The pressure switch further includes a circuit board comprising first and second electrical terminals. The snap disc forms a closed circuit between the first and second terminals when the snap disc is in the first shape and forms an open circuit when the snap disc is in the second shape.
According to another aspect of the present invention, the pressure switch includes a housing having walls defining a fluid chamber adapted to receive a fluid, and a snap disc having a front surface in pressure communication with the fluid chamber. The snap disc is responsive to switch states between first and second shapes based on a pressure set point, and includes an electrically conductive rear surface. The pressure switch further includes a first electrical terminal and a second electrical terminal. The first and second electrical terminals form a closed circuit with the conductive rear surface of the snap disc when in a first shape and form an open circuit when in a second shape. Accordingly, the pressure switch of the present invention employs a snap disc that offers high reliability and requires minimal moving components.
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Easthom Karl D.
Klaus Lisa N
Price Heneveld Cooper DeWitt & Litton
Sherwood-Templeton Coal Company, Inc.
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