What are the causes of a pressure gauge reading “in the red” on a reservoir cylinder?
The pressure gauge is called a “temperature compensating gauge” and its function is to compensate for an increase or decrease in temperature. So even if the temperature increases, as long as the gauge needle falls within the band of the compensating cursor, the bottle pressure is within manufacturers’ limits, whether it be high or low pressure. As an example, cold weather can cause the needle to display a lower pressure than the pressure in the bottle. But this is ok because the compensating cursor will indicate the proper pressure for that temperature. There is a pressure problem if the gauge needle is not within the compensating cursor band. The two common causes of the pressure being incorrect is leakage and not allowing the reservoir assembly to settle prior to installation on the aircraft.
