Cone disc lock-on switch

Claim 1

Switch means responsive to differential pressure between first and second hydraulic systems comprising: a housing having a bore therein; a piston located in said bore having a pair of opposed faces; first and second chambers located in the borE defined by the respective faces on the piston and corresponding ends of the bore, said first and second chambers being in fluid communication with said first and second hydraulic systems respectively; an electrical terminal carried by the housing for transmitting a signal to a warning device; a plunger member retained in the housing having an end extending into said bore, said piston displacing said plunger from a first position to a second position in response to movement of said piston from a pressure differential between the first and second hydraulic systems; truncated conical disc means surrounding said plunger means, said truncated conical disc means being correspondingly moved from an inactive position to an active position as said plunger member is shifted from said first position to said second position, said truncated conical disc means in said active position providing continuity between said housing and said electrical terminal to permit said electrical signal to activate said warning device, said truncated conical disc means being maintained in the active position through inherent resiliency until manually repositioned regardless of said plunger member later shifting between said first and second positions.