1453 Pressure Measurements

If equipment is not operating in its proper pressure range, it can be damaged or the equipment it serves can be damaged. This is true whether the pressure being measured comes from oil (compressors or lift trucks), fuel (boilers), steam (boilers), or other sources. Measuring pressure using portable equipment generally requires that the equipment to be measured be equipped with a fitting specifically designed for pressure-sensing equipment. With such fittings in place, it is possible to use a Bourdon tube or a diaphragm gauge for routine inspections. Where information is to be available at

Building envelope Boilers

Steam traps

Heating, ventilating, and air conditioning


Lighting Hot water Air compressors any time, or when the readings are to be taken so often that portable pressure-sensing equipment becomes a nuisance, it may be desirable to permanently install a Bourdon tube or a diaphragm gauge, or to rely on a manometer.

Bourdon Gauge

This common pressure gauge consists of a curved tube closed at one end with the other end connected to the pressure to be measured. When the pressure inside the tube is greater than the pressure outside the tube, the tube tends to straighten, and the amount of change in length or curvature can be translated directly into a gauge reading. Such gauges are available in many pressure ranges and accuracies.

Diaphragm Gauge

If the pressure inside a bellows or on one side of a diaphragm is greater than the pressure outside the bellows or on the other side of the diaphragm, the bellows or the diaphragm will move. The amount of movement is related to the pressure between the inside and outside the bellows (or on the different sides of the diaphragm). These pressure gauges are also very common.


If a glass tube has liquid in it, and if one end is open to the air and the other end is exposed to a pressure other than air pressure, the end with the higher pressure will have a lower liquid level. This kind of gauge can be mounted across a filter bank to indicate when a clogged filter is causing pressure to build up, or it can be mounted in a place where a much higher pressure is to be measured. If the tube is inclined, a smaller pressure difference is detected, as in the inclined-tube manometer. These gauges are easy to read, easy to maintain (the glass must be kept clean, and the inlet and outlet holes must be kept clear of debris), and inexpensive.

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