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How to Drain Your Air Tanks



The following information was taken from a Spartan chassis service seminar. While specific to Spartan chassis, the same principles should apply to other brands as well because air systems are very similar on all motorhomes that have air brakes and suspension.

One common misconception is that the main purpose in draining air tanks is not to remove the moisture from the system, but really to test the integrity of the system. If the air drier is doing it's job there should be very little, if any, moisture exiting the tanks when the manual tank drains are operated. If you do see excessive moisture coming out it is time to service the air drier. Normally you would pull the tank drain lanyards for a few seconds, then release them. Any moisture within the tank will settle to the bottom and be expelled. However, the Spartan procedure goes a step farther and tests the check valves within the air tanks. This requires complete draining of the tanks rather than a brief spurt. Following the procedure is necessary to allow proper testing of the check valves between the tanks. Note that there are two physical air tanks on the Spartan chassis. One of the tanks is divided into two partitions to form both the wet tank and primary tank. so, in effect there are three tanks.

Test Procedure:

  1. With engine off, make sure both air gauges read 70 PSI or less. If they read higher, pump the brake pedal until the air pressure gauges read 70 PSI or less.
  2. Start the engine and run at high idle (1,200 RPM or higher) until the Air Drier purges in the rear of the vehicle.
  3. Turn the engine OFF, but leave the ignition switch ON so that the gauges are powered up and reading the air pressure.

In the following steps, pull each lanyard until the tank is empty and the hissing stops.

  1. Pull the SILVER lanyard (wet tank). There should be no significant moisture and neither of the gauges should change.
  2. Pull the GREEN lanyard (primary tank - rear air). There should be no significant moisture and one gauge should drop to zero.
  3. Pull the RED lanyard (secondary tank - front air). There should be no significant moisture and both gauges should now be at zero.


Submitted by Richard King - 8/16/10

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