5 10 15 20 30 0 25 5 10 15 20 30 0 25 5 10 15 20 30 0 25 NON-RELAY THERMOSTAT RESTRICTOR DIAL BIMETAL PILOT ORIFICE MAIN AIR TEST GAUGE VALVE FULLY OPEN RESTRICTOR DIAL BIMETAL PILOT ORIFICE MAIN AIR TEST GAUGE VALVE FULLY CLOSED RESTRICTOR DIAL BIMETAL PILOT ORIFICE MAIN AIR TEST GAUGE VALVE MODULATING Non-relay thermostats are usually one pipe as illustrated; however, they are available as two pipe thermostats. As two pipe, they usually are two one pipe thermostats built into one unit allowing the heating and cooling functions separate control with a dead band. Non-relay thermostats may be direct or reverse acting depending on if the function is heating or cooling and if the valve is normally open or normally closed. The restrictor is usually either a .005” or a .007” orifice; therefore, this type of instrument builds its branch line signal much more slowly than a relay instrument. A small leak in the branch tubing or the valve diaphragm will cause lack of control much sooner than with relay type thermostats. The test gauge illustrated is not normally installed in a building. The service technician calibrating the thermostat plugs his test gauge into the branch line of the thermostat allowing 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. 3.20
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