Boiler Temperature Gauge and Boiler Pressure Gauge

Instrumentation on a boiler is very important to help trained personnel evaluate boiler performance. Most of this data is provided by temperature and pressure gauges. 

Pressure gauges are used to determine:

  • Steam Pressure
  • Feedwater Pressure
  • Oil Pressure
  • Gas Pressure
  • Draft Pressure

boiler temperature gauges

Pressure may be recorded as gauge pressure or as absolute pressure. Gauge pressure is the pressure above that of the atmosphere. Absolute pressure is the pressure above zero pressure, equal to gauge pressure plus the atmospheric pressure. At sea level, atmospheric pressure is 14.7 psi.

Pressure gauges include many pressure measurement devices including bellows, Bourdon tubes, capsule elements and diaphragm element gages; detailed form for analog or needle dial face gauges.

Temperature Gauges are used to determine:

  • Feedwater Temperature
  • Oil Temperature
  • Water Temperature
  • Flue Gas Temperature

Temperature can be reported as degrees Fahrenheit, degree Centigrade or as Absolute temperature. To convert from Fahrenheit to absolute temperature use the following formula:
oFa = oF + 459.7 
To convert from Centigrade to Absolute Temperature you would use the following formula:
oCa =oC + 273 

Temperature gauges can be classified as either mechanical in design or electronic. Mechanical temperature gauges include bi-metallic or filled system design. A bi-metallic thermometer uses two dissimilar metals joined together. Since these metals are not the same their co-efficient of expansion will be different allowing the composite metal strip to bend in the direction of the metal with the lower co-efficient. This is predicable and repeatable and therefore can be scaled. Bi-metal temperature gauges are inexpensive and are commonly used in boiler applications.

Filled system thermometers utilize an expandable liquid or, in some cases, a gas that are sealed hermetically within an enclosure. As heat is added or taken away the gas or liquid will expand or contract causing a tube to stretch or contract over a scale. This type of system is commonly used for switch activation.


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P.C. McKenzie Company
P.O. Box 112638
Pittsburgh, PA 15241
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P.C. McKenzie Company
1365 McLaughlin Run Road
Pittsburgh, PA 15241