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3. Close Vacuum Control, Vacuum Vent, Pressure Control, and Pressure Vent
valves. Open Crossbleed valve.
4. Actuate the Vacuum Pump until a desired level of vacuum is seen on the Vacuum
Reservoir gauge (generally -15 to -20 inHG). Actuate the Pressure Pump until the
Pressure Reservoir indicates 15 PSI or more.
5. Gently open the Vacuum Control valve to cause the altitude to climb.
6. DO NOT exceed the climb rate of the aircraft VSI indicator, or the airspeed
indicator limits. The VSI is a very delicate instrument.
7. Climb to the desired altitude(s) per the test to be performed.
8. Close the Vacuum Control valve, and after allowing a few seconds for
stabilization, compare the aircraft altimeter with the test box.
9. When at the appropriate altitude (generally 18,000 feet) perform a leak check. If
the static system shows leakage, be careful to not exceed the VSI rate. Be
prepared to open the Vacuum Control valve if needed, to prevent excessive VSI
indication.
10. To display an airspeed, close Crossbleed valve and gently open Pressure valve
until desired airspeed is indicated. Close Pressure valve.
11. To return system to ambient pressure, ensure Crossbleed valve is open. Then
gently open the Pressure Vent valve to return the system pressure to ambient
pressure. Do not exceed the VSI or airspeed indicator limits.
Note: if an altitude lower than ambient pressure is desired, do steps 1-4 above. Gently
open the Pressure Control valve to pressurize the system, thereby causing the
altimeter to decrease in altitude. Open the Vacuum Vent valve to return to ambient
pressure.
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