2.3 TRAINING YOUR EAR TO THE DIFFERENT SOUNDS OF A THERMOSTAT MAY ASSIST YOU IN FINDING LEAKS The normal air usage of a relay thermostat produces a local hissing noise, while air passing through a thermostat relay, to a leaking diaphragm, makes a lower rushing sound. To train your ear, at a practical level, find a thermostat in a non-critical location. (1) Turn a direct acting thermostat to full heat and listen to the hissing sound of the pilot air (approximately .5 SCFH of compressed air) which most thermostats are designed to bleed. (Powers "D" stats do not bleed any air except when reducing its branch pressure.) (2) Turn the setting of the thermostat down and listen to the air rushing through the thermostat relay to fill the diaphragm of the controlled device. The air volume you hear is about 27 SCFH to 70 SCFH, depending on the model. (See T4002 consumption graph, page 3.27.) The sound of the rushing air will taper off to silence when the diaphragm is completely filled at the main supply line pressure. (3) Now you are going to simulate a blown diaphragm. Turn the thermostat down completely. Go to the controlled device (valve or damper actuator) and disconnect the airline. Go back to the thermostat and listen to the sound it is making. This is the same sound the thermostat makes while filling the diaphragm, except it does not taper off to silence because the air continues to rush to atmosphere via the simulated (or real) blown diaphragm. Knowing the difference between the sounds of a thermostat assists greatly in finding and correcting leaks. REMEMBER TO RECONNECT THE BRANCH LINE AT THE VALVE OR DAMPER ACTUATOR AFTER DOING THIS EXERCISE. CAUTION Be sure that you do not turn off an exhaust fan or supply fan without checking with the building management. You may cause serious problems if the wrong fan is turned off at the wrong time. Be sure to check with the building management for the appropriate time to install the flow meter. Advise the building management of the likely impact on parts of the building when control air is turned off during the meter installation. (For example: The heating will likely open fully, fresh air and exhaust air dampers will close, etc.) 9-168
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