5 10 15 20 30 0 25 5 10 15 20 30 0 25 5 10 15 20 30 0 25 RELAY THERMOSTAT DIAL BIMETAL TEST LEAK PORT GAUGE (FLAPPER NOZZLE) MAIN AIR .005” ORIFICE EX. EXHAUST BRANCH SEAT LINE MAKEUP SEAT VALVE FULLY OPEN DIAL BIMETAL TEST LEAK PORT GAUGE (FLAPPER NOZZLE) MAIN AIR .005” ORIFICE EX. EXHAUST BRANCH SEAT LINE MAKE UP SEAT VALVE FULLY CLOSED DIAL BIMETAL TEST LEAK PORT GAUGE (FLAPPER NOZZLE) MAIN AIR .OO5” ORIFICE EX. EXHAUST BRANCH SEAT LINE MAKE UP SEAT VALVE MODULATING Relay thermostats are usually two pipe, but some can be three pipe found in unitventilators, typically in schools. (see unitventilator sheets) Most relay thermostats are similar to the illustrations on this page. Both day/night and summer/winter thermostats are more complex. Night and day set points are both direct acting and the summer and winter are usually reverse and direct acting respectively. Working normally, relay thermostats bleed approximately the same amount of compressed air as non-relay thermostats via the .005” orifice. Through the makeup seat, some relay thermostats pass up to 100 times as much air as non-relay thermostats. The test gauge is not normally installed in a system. Service technicians plug their test gauges into the thermostat only during calibration. When calibrating the thermostat you must know the temperature of the room at the thermostat. Plug your gauge into the branch line. Turn the dial all the way up and all the way down witnessing that the pressure goes from zero PSIG to the main air pressure. Then set the dial at the actual room temperature. Then adjust the branch pressure to mid-range of the device being controlled. Then breathe your warm breath on the thermostat checking that the pressure increases for direct acting thermostats and decreases for reverse acting thermostats. Then set the dial to the desired temperature for the room and put the cover back on the thermostat. 3.21
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