CONTROL RELAYS _________________________________________________________________________________________ LOW HIGH SELECTOR SELECTOR (1) (B) INPUT OUTPUT INPUT OUTPUT (M) INPUT INPUT _________________________________________________________________________________________ AIR MULTI/HIGH/LOW SWITCHING SELCTOR VALVE PILOT (P) NC C SIX INPUTS NO Low selectors receive two input signals and produce an output signal matching the lower input. Low selectors often can be used as a volume booster relay, depending on the manufacturer. High selectors receive two input signals and produce an output signal matching the higher of the two inputs. Air switching valves are open from the NO to the C port when the pilot signal is lower than the valve’s spring range. The valve is open from the NC to the C port when the pilot pressure is higher than the valve’s spring range. Gradual acting air valves must have a two position pilot signal (0 PSIG or 15-20 PSIG). Snap acting air valves may have a gradually changing or two position pilot signal. Some air valves have adjustable switching points. H M L Multi-high/low selectors receive more than two input signals. Manufacturers allow a variety of options. The highest signal is duplicated as the high output signal and the lowest signal is duplicated as the low output signal. Both the multi-high and multi-low can be built with check valves and a .005” restrictor. Flow from each of the selected signals, through a check valve, to a common line and the .005" restrictor bleeding to atmosphere from the common line will produce the highest signal. Flow through check valves, to each of the selected signals from a common line which has main air entering the common line through the .005" restrictor produces the lowest signal on the common line. 2.13A
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