Image Number 4 for United States Patent #4900883.
In a preferred embodiment, a fluid-operated switch continuously and selectively adjustable over both a pressure range and a vacuum range. The switch includes a diaphragm enclosed in a housing, a first side of the diaphragm communicating with the fluid. On the second side of the diaphragm, actuator means are provided which actuate an electrical switch when the diaphragm is flexed by changes in the pressure or vacuum of the fluid. A main spring provides adjustable resistance to motion of the actuator means in the direction of diaphragm flexure corresponding to an increase in pressure, while a counterspring provides resistance to motion of the actuator means in the direction of diaphragm flexure corresponding to an increase in vacuum. Adjustment of the set point of the switch is effected through adjusting the degree of compression or relaxation of the springs by adjusting a threaded bonnet on the housing. At one degree of compression, the spring forces are balanced and further compression will selectively shift the set point into the pressure region, while relaxation of the springs from that balance point will selectively shift the set point into the vacuum region. Thus, one valve body with one set of internal elements can be field adjusted for either pressure or vacuum operation.