Testing The Aircraft Pitot And Static Systems Simultaneously; Using The E.p.r. Function - PRESTON PRESSURE PS-500 User And Maintenance Manual

Testing the Aircraft Pitot and Static systems simultaneously

Note: First ensure pitot system does not leak by performing Pitot system test on page 14.
1. Turn on the power to the PS-500.
2. Connect the Vacuum Port to the aircraft static port, and the Pressure Port to the
aircraft pitot port. Set the aircraft altimeter to 29.92 inHg (1013.3 mB).
3. Close Vacuum Control, Vacuum Vent, Pressure Control, and Pressure Vent
valves. Open Crossbleed valve.
4. Operate the Vacuum Pump switch until a desired level of vacuum is seen on the
Vacuum Reservoir gauge (generally -15 to -20 inHG). Turn Pressure Pump switch
on until the Pressure Reservoir indicates 10 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.
 Using the E.P.R. function
The EPR function is used to test engine pressure ratios. This ratio is the mathematic result
of: High Pressure/Low Pressure. The PS-500 test box will display the low pressure, the
high pressure (both in PSI), and the resulting EPR. To use the EPR function, proceed as
follows:
1. Turn on the test box.
2. Close all of the valves, including the Crossbleed valve.
3. Connect the Vacuum port to the low pressure to be tested.
4. Connect the Pressure port to the high pressure to be tested.
5. Cycle through the Units on the Airspeed side until in the EPR mode. Read the
EPR values displayed.
Note: Do not exceed 16.75 PSI on the high pressure side, to avoid sensor damage.
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