Product: 0-15 PSI Liquid Filled Gauges
Problem: Gauge does not read or gauge does not read correctly.
Solution: Vent the gauge.
For an accurate pressure reading on a liquid filled gauge you should vent the gauge before taking a pressure reading. You should vent the gauge whenever the temperature of the gauge has changed significantly (either heated up or cooled down).
Venting is easy to do and takes seconds. To vent the gauge carefully push the side of the vent plug (the part under the plug lip) with your thumbnail to equalize the gauge case pressure with the atmosphere (reference pressure). Do not remove the plug. It is OK if some liquid also escapes, just wipe any liquid that escapes off with a cloth. Loss of the liquid fill will not affect operation of the gauge. See photo below for an illustration of how to vent a gauge:
Why do I need to vent the gauge?
All mechanical liquid filled gauge cases are sealed (to keep the liquid in) so as they heat up pressure will build up in the case (approx 1psi for every 30-40F temperature change).
This case pressure exerts a force on the mechanical movement and offsets the actual process pressure. This effect is typically small and therefore is only noticed when measuring low pressures (i.e. on a 0-15 psi gauge).
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