CDL · Air Brake Inspection

How often should you drain the air tanks?

Reviewed by Jordan Morley, Editorial Lead at 247SimpleTests. Written by the 247SimpleTests Editorial Team from the official source material cited on every question.

Correct answer

Daily, or whenever an automatic drain valve is unavailable; more often in humid or freezing conditions

A Once a week
B Daily, or whenever an automatic drain valve is unavailable; more often in humid or freezing conditions
C Only at annual inspection
D Only when the tank pressure exceeds 150 psi

Why this is the answer

Air tanks should be drained every day. Most modern trucks have automatic drain valves that release water and oil periodically without driver action, but drivers should still verify these are functioning. If automatic drains are not present or have failed, drain manually by opening the petcock at the bottom of each tank. The wet tank (supply tank) collects the most water and is the most important to drain. In humid weather or after long compressor cycles, more water accumulates. In freezing weather, undrained water can freeze in the lines or valves and block air flow, causing brake failures. Allowing water to accumulate also corrodes tanks and components over time.

Source: FMCSA CDL Manual 5.1.4 Draining Air Tanks

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About this topic: Air Brake Inspection

Air brake inspection is its own structured procedure: build-up, leakage rate, low-air warning, and spring-brake activation must all check out before you drive. This is one of 13 Air Brakes questions on air brake inspection, each with a full explanation on a single study page.

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How often should you drain the air tanks?

Why this is the answer

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About this topic: Air Brake Inspection

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