On many pressure gauges there is a vent valve at the top of the case, at WIKA in the form of a yellow lever.
Upon delivery of the instrument, the valve is closed and must be opened during commissioning to ensure correct functioning of the pressure gauge.
The internal pressure of a hermetically sealed pressure gauge changes due to temperature fluctuations, for example caused by exposure to direct sunlight. This pressure in the case leads to inadmissibly high accuracy deviations for the measuring instrument. Pressure compensation between the pressure gauge case and atmospheric pressure is ensured via the vent valve.
However, not all WIKA pressure gauges have a vent valve: If higher protection classes are required, pressure compensation takes place via a diaphragm attached to the inner rear wall of the case. For pressure ranges above 16 bar, the measuring error produced by the pressure build-up inside the pressure gauge case can be neglected – the pressure gauge will still work within its specified class accuracy.
Why is the yellow lever closed ex works? Pressure gauges are usually transported in horizontal position. If the vent valve of filled pressure gauges were left open, the filling liquid would leak out of the instrument.
