9
3. Turn on the power, and then actuate the Vacuum Pump until the Vacuum
Reservoir gauge reads approximately -15 inHG.
4. Gently open the Vacuum Control valve to make the Altimeter section climb. This
climb may be done rapidly without damage to the sensor.
5. When the Altimeter reads at least 18,000 feet, gently close the Vacuum Control
valve.
6. Wait for about 60 seconds for internal pressures to stabilize. Then perform a leak
check.
7. The leak check function will activate and begin to monitor the leak rate. Verify
that the PS-425 does not leak exceeding 100 feet per minute. Write down the leak
rate for future reference. (Subtract this value from the total leak rate when testing
the aircraft, to arrive at the aircraft’s leak rate.)
8. Gently open the Vacuum Vent valve to bring the test box back to ground
(ambient) pressure.
Pre-test the pressure system of the PS-425 test box according to the following steps:
1. Turn on the power to the PS-425.
2. Ensure the PS-425 is not connected to any external hoses or devices.
3. Close the Vacuum Control, Vacuum Vent, Pressure Control, Crossbleed valve,
and Pressure Vent valves.
4. Actuate the Pressure Pump until the Pressure Reservoir gauge reads
approximately 15 PSI.
5. Gently open the Pressure Control valve to make the Airspeed section climb. This
climb may be done rapidly without damage to the sensor.
6. When the Airspeed reads at least 300 knots, gently close the Pressure Control
valve.
7. Wait for about 30 seconds for internal pressures to stabilize. Activate the leak
check function to monitor the leak rate. Verify that the PS-425 does not leak
exceeding 2 knots per minute. Write down the leak rate for future reference.
(Subtract this value from the total leak rate when testing the aircraft, to arrive at
the aircraft’s leak rate.)
8. Gently open the Pressure Vent valve to bring the test box back to ground
(ambient) pressure.
Testing Aircraft Pitot System Only
1. Turn on the power to the PS-425.
2. Connect the Pressure Port to the aircraft Pitot system.
3. Close Pressure Control, Pressure Vent, and Crossbleed valves. Open Vacuum
vent valve.
4.
Actuate the Pressure Pump until the Pressure Reservoir indicates 15 PSI or more.
5. Gently open Pressure Control valve until desired speed(s) are achieved.
6. Compare the airspeed of the PS-425 box to the airspeed indicated in the aircraft.
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