Rhomberg Instrumentation

Key Factors for Gauge Selection

Many factors should be evaluated including temperature, vibration, process conditions,  pulsation and corrosion, but by carefully considering the 7 key factors outlined below, the chances of correct selection will increase significantly.

Process Medium
The process medium to which the gauge will be exposed is especially important when using  a thin walled Bourdon tube because, if the wrong materials are selected, corrosion may occur which could lead to catastrophic failure. Materials which display the essential combination of properties (good spring memory, easy to form, easy to join, reasonably priced) are phosphor bronze, 316 stainless steel and Monel. Where these materials can’t satisfy the application, a diaphragm seal (gauge isolator) can be added to prevent the process media from contacting the Bourdon tube. This protects the gauge from corrosion attack, and also prevents viscous or dirty media from clogging the small bore Bourdon tube. The only limitation in using a diaphragm seal is that it typically degrades the accuracy of the pressure gauge by an additional 0,5 % of the full scale deviation. Pressure Gauge Range
It is important to select a pressure range which accommodates all anticipated pressure  swings, and which prevents excessive needle movement. It is recommended to confine normal operating pressure to 25 % – 75 % of scale. With fluctuating pressures (e.g.  pulsation caused by a pump or compressor), the maximum operating pressure should be
lower (50 % of the full range). Gauges in severe service should be liquid filled and throttled
to reduce Bourdon tube stresses. To minimize sensing element stress and to extend the life of the gauge use internal throttle screws, pulsation dampeners, pressure snubbers, gauge savers or diaphragm seals.