Charles Dosh WA1 2014JUN ELT-308-OL009 7. The toggle switch is a general classification of switch that means that when a state change occurs to a switch, the switch maintains the position until another rest state change occurs. A pushbutton, rocker and slide can all be considered toggle switches, if they are built in such a manner. Rocker and slide switches are similar in that both states can be represented at the same time depending on the position of the switch whereas a pushbutton switch can still be a toggle switch but both states re “stacked” onto each other rather than a side by side view. 12 Limit switches, Drum Switches, Pilot type push buttons 24 Pneumatic time delay relays operate by the steady release of air causing a bellows to move. Once the air is eliminated contact is made or broken. Timing relays operates as a TON, time off delay or a TOF delay depending on their normal state conditions. 34 As basic as it gets, the difference is based on the number of input/output ports. There are multiple position valves that support the higher number of ports. 39 In a fueling system, the flow switch is utilized to verify that the pump’s discharge is flowing when the pump is called. In the same fuel system, the fuel loop’s pressure is monitored and if the pressure switch trips, it means the pressure has dropped below a set point and a pump will need to be started to reset the switch. The temperature on a motor/pump is monitored such that if a temperature switch is opened (motor is too hot), the motor will not be allowed to start, or will shut down if already running. A vacuum switch can be utilized to specify within a sealed tank that proper ventilation is plugged or if an air eliminator is malfunctioning if it trips. A level sensor on a tank can designate that you have hit a lowlow point, at which point vales may shut or pumps may be stopped in order to ensure the safety of equipment. 44 A NO relay contact vs. a NC relay contact designates the standard condition of contacts if there is no power applied to the coil. A closed relay is one that has the proper power applied to its coil causing it to change states, where an open relay is one that does not have the proper power applied to its coil. 4.