Mechanical displacement type flow switch with fluid state maintenance heating means

Claim 1

In a fluid flow responsive device having a movable mass element disposed in the flow path of a fluid medium to be displaced by the force of flow resistance in accordance with the existence, variation or cessation of fluid medium flow, wherein said medium has a tendency to thicken or congeal below a given temperature, the improvement comprising: a movable mass element having a sensing surface disposed within said flow path to be impinged upon by the flow of said fluid medium; means supporting said movable mass element to be displaced in accordance with the force exerted against the sensing surface by the impinging flow from a normal position indicative of the absence of flow; indicating means responsive to the displacement of said movable mass element from said normal position for registering the flow of the fluid medium past said movable mass element; and heating means mounted in heat exchange relationship with said movable mass element and the volume of said fluid medium in said flow path adjacent thereto to maintain the fluid medium adjacent said movable mass element above said given temperature.