An automatic integrity tester is routinely used in pharmaceutical production to test the integrity of sterilizing filters. Among other factors, test accuracy is affected by gas temperature changes on the upstream side of the filter. During the integrity test, the upstream gas temperature changes considerably when pressurizing or depressurizing the gas in the filter housing, which is part of the integrity test protocol.

Thermocouples were placed inside a filter housing to monitor the gas temperature changes during pressurization and depressurization. It was found that the air temperature inside the filter housing increased from 22°C to over 70°C when pressurized from 0 to 60 psig. The air temperature inside the housing dropped from 22°C to -45°C when depressurized from 56 to 0 psig. The theory of gas temperature changing with pressure was studied and the experimental values of gas temperature changes were well within the limits projected from adiabatic models. Understanding the correlation between pressure and instantaneous temperature changes is critical for the design of automated test equipment.