When brake air tank gets to approximately _____ to _____ psi the air dryer should be heard discharging a burst of air.

When brake air tank gets to approximately _____ to _____ psi the air dryer should be heard discharging a burst of air.

• A. 100-110
• B. 110-115
• C. 130-135
• D. 120-125

Answer: (D)

Air dryers remove moisture by purging condensate during a specific phase of the system’s pressure cycle. When the brake air tanks have been charged to the upper end of the normal operating range, the purge valve opens and a burst of air is vented to carry out moisture. That audible burst happens at this higher-pressure point because the system is still pressurized enough to vent without dropping pressure too far, and the purge cycle is timed for this part of the cycle. The other ranges would occur earlier in the charging cycle or after the system has already moved past the purge point, so you wouldn’t hear the characteristic burst then. So the purge audible burst is expected near the upper end of the high-pressure range, which is why this range is correct.

Air dryers remove moisture by purging condensate during a specific phase of the system’s pressure cycle. When the brake air tanks have been charged to the upper end of the normal operating range, the purge valve opens and a burst of air is vented to carry out moisture. That audible burst happens at this higher-pressure point because the system is still pressurized enough to vent without dropping pressure too far, and the purge cycle is timed for this part of the cycle.

The other ranges would occur earlier in the charging cycle or after the system has already moved past the purge point, so you wouldn’t hear the characteristic burst then. So the purge audible burst is expected near the upper end of the high-pressure range, which is why this range is correct.