HVACR NewsMagazine December 2017

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Ventilating Systems is quite small …… but very important. This pressure seldom amounts to as much as .1 PSI and most of the time is less than half this amount. Never the less, this pressure has a large influence on the performance of the fan and the delivery of air through- out a duct system. In order to remember how inches of water column is derived, remember that One PSI will support a column of water 2.31 feet high or 27.7 inches . As such One PSI is equal to 27.7 inches of water. Even a pressure as low as .05 PSI will support a column of water 1.39 inches (27.7 x 0.05) Gauges which are used to derive this small pressure are known as a

pressure. If you then divide the 3- inches by 27.7 this results in a pressure of .108 PSI. Another form of gauge to measure this small pressure is called an incline manometer. In this meter which is quite common in the HVAC Industry , the tube is inclined (on one end) at a variety of angles, however all incline manometers will be open on

Dwyer 250 - AF

the elevated end to the atmosphere. On the incline monometer that I have used for years, the fluid in the incline monometer has red dye, so it is easier to see and read. Today, manometers are available in a digital format and read out and are available from many suppliers. In closing, if you do not have some form of manometer on your service

U-Tube or incline gauge (manometers). One end of the tube is open to the atmosphere and the other is connected to the air duct. If the pressure of the air inside the duct is slightly greater than the surrounding atmospheric pressure, the (U-Tube) water column will be down

Dwyer

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in one leg of the U and up in the other leg of the U. As such if the air pressure from the duct forces one leg (in the U-Tube) down 1.5 inches with the other leg going up 1.5 inches this results in 3-inches of water column

TEC DG 1000 Digital Manometer

vehicle, I strongly encourage you to get one. It is a necessity for checking duct pressures, gas pressures and