Pressure responsive switch actuating mechanism

A switch actuating mechanism including a movable actuating element which is movable between an inoperative location and an operative location to actuate a switch;

• a pressure responsive system including a movable stop, urging means urging the actuating element towards the stop whereby the actuating element is normally urged against the stop, means responsive to pressure of a flow of fluid comprising a movable wall having one side to which the fluid pressure is subjected and means by which movement of the movable wall causes movement of the stop whereby the location of the stop is controlled in accordance with the fluid pressure, said means by which movement of the movable wall causes movement of the stop comprising a rigid link which has one end cooperating with the other side of the wall so that it moves with the wall when the wall moves and which extends away from the wall oblique to a line of action of the fluid pressure loading on the wall, resilient means which exert a load which is applied to the link at a location thereon spaced from said one end, whereby the tend to reduce the angle included between the link and said line of action, and constraining means which, in conjunction with the wall and the resilient means, constrain the link against movement relative to the wall when the wall is stationary so that the system is static and the fluid pressure loading on the wall overcomes the counterload applied thereto by the resilient means acting through the link;
• and a time delay mechanism which is operable to delay movement of the actuating element following movement of the stop in response to certain pressure changes;
• the pressure responsive system being set in one condition in which it locates said stop in one location when the fluid pressure is within a range bonded by ambient pressure and a predetermined switching pressure, even when the fluid pressure is changing, and being convertible to another condition to move said stop to another location when the fluid pressure reaches said predetermined switching pressure whereby said actuating element is released for delayed movement into abutment with said stop at said other location to actuate said switch, there being virtually no movement of said location on the link until said predetermined switching pressure is established, a large rapid movement of said location on the link when said predetermined switching pressure is established and a snap back to said location if the pressure falls significantly below said switching pressure.

A switch actuating mechanism including a movable actuating element which is movable between an inoperative location and an operative location to actuate a switch;

• a pressure responsive system including a movable stop, urging means urging the actuating element towards the stop whereby the actuating element is normally urged against the stop, means responsive to pressure of a flow of fluid comprising a movable wall having one side to which the fluid pressure is subjected, means by which movement of the movable wall causes movement of the stop whereby the location of the stop is controlled in accordance with the fluid pressure, said means by which movement of the movable wall causes movement of the stop comprises a buckling link which is a linkage comprising two link elements hinged together, one of the link elements having one end cooperating with the other side of the wall so that it moves with the wall when the wall moves, and extending away from the wall oblique to a line of action of the fluid pressure loading on the wall, the other link element being anchored at a location spaced from the hinge, and resilient means which exert a load which is applied to said one link element at a location thereon spaced from said one end whereby to tend to reduce the angle included between said one link element and said line of action and thereby to hold the two link elements against movement relative to the wall when the wall is stationary so that the system is static and the fluid pressure loading on the wall overcomes the counterload applied thereto by the resilient means acting through said one link element, a pair of fixed stops which are spaced apart, and an arm which is fixed to one of the buckling link elements and which projects between the fixed stops so that movement of the buckling link elements in either direction is limited by abutment of the arm with a respective one of the fixed stops, the distance between the fixed stops being sufficiently small to ensure that the range of movement of the buckling link elements and the common hinge between them is less than enough for the buckling link to go `over centre`;
• and a time delay mechanism which is operable to delay movement of the actuating element following movement of the stop in response to certain pressure changes;
• the pressure responsive system being set in one condition in which it locates said stop in one location when the fluid pressure is within a range bounded by ambient pressure and a predetermined switching pressure even when the fluid pressure is changing and being convertible to another condition to move said stop to another location when the fluid pressure reaches said predetermined switching pressure whereby said actuating element is released for delayed movement into abutment with said stop at said other location to actuate said swtich, there being virtually no movement of said location on the link until said predetermined switching pressure is established, a large rapid movement of said location on the link when said predetermined switching pressure is established and a snap back of said location if the pressure falls significantly below said switching pressure.