An actuating apparatus having a signal transmitter and a mechanical operating element, wherein the mechanical operating element includes a first position that is stable over time and a second position that is stable over time, wherein the mechanical operating element, in the case of a movement from the first position that is stable over time into the second position that is stable over time, actuates the signal transmitter, and wherein the signal transmitter, upon actuation, causes a first signal change followed by a second signal change of an output signal, and an evaluation circuit detects an actuation of the mechanical operating element based on the first signal change and the second signal change.

An actuating apparatus having a signal transmitter and a mechanical operating element, wherein the mechanical operating element includes a first position that is stable over time and a second position that is stable over time, wherein the mechanical operating element, in the case of a movement from the first position that is stable over time into the second position that is stable over time, actuates the signal transmitter, and wherein the signal transmitter, upon actuation, causes a first signal change followed by a second signal change of an output signal, and an evaluation circuit detects an actuation of the mechanical operating element based on the first signal change and the second signal change.

A deadman switch system includes a primary deadman switch actuator and a secondary deadman switch actuator for controlling the flow of an air/abrasive mix through a flow line of a delivery system. The secondary deadman switch is positioned in series with a primary deadman switch actuator such that the controlled flow will not function unless first the primary deadman switch and then the secondary switch are closed. The preferred embodiment of the switch is a low-profile configuration adapted to be mounted in axial alignment with the flow line in a manner to minimize interference with normal operation of the system. The switch can include multiple open/close elements, for selectively controlling different flow functions.