There are five primary items needed to properly select a pressure gauge:
- Pressure Range – What pressure scale needs to be measured?
- Dial Size – How large of a dial diameter is needed?
- Connection Type – What size and orientation of connection is required?
- Material – Should the wetted parts be brass or stainless steel?
- Accuracy – What accuracy of measurement is required?
What pressure scale needs to be measured? Generally speaking the gauge pressure span should be double the normal operating pressure of the application it is used on. In other words, if the normal pressure of the system is 150 psi, you should select a pressure gauge with a 300 psi range. If a gauge with the exact range is not available, it is best to round up. For example, if the normal system pressure is 100 psi and a 200 psi range is not available, it is preferable to round up to a 300 psi gauge.
2. Dial Size
How large of a dial diameter is needed? Dial size is simply the diameter of the circular face of the pressure gauge. When selecting a dial size, ease of reading and space available to mount the gauge are primary concerns. Generally speaking, the larger the dial, the more expensive the pressure gauge. The most common dial size is 2-1/2”. Dial sizes can range from 1” up to 10”.
3. Connection Type
What size and orientation of connection is required? The orientation of the connection refers to its location on the pressure gauge. Choices of orientation are generally lower mount (protruding from the bottom of the gauge at the six o’clock position) or back mount (protruding from the rear of the pressure gauge). The vast majority of pressure gauges are sold with male pipe thread connections ranging in size from 1/8” NPT to ½” NPT with ¼” NPT being by far the most common.
Should the wetted parts be made of brass or stainless steel? The wetted parts of the pressure gauge are the materials that come in contact with the fluid or gas being measured. Stainless steel is more durable and more resistant to corrosion. Brass is more economical.
What accuracy of measurement is required? Pressure gauges are available with accuracies ranging from +/- 3/2/3% to +/- 0.1% of span. The higher degree of accuracy required, the more expensive a gauge will be. Common accuracies are 2-1/2%, 1%, and 0.5% of span.
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