Continental Motors GTSIO-520 SERIES Operator's Manual page 39

M7 3-19. The differential pressure tester is designed to check the
compression of aircraft engines by measuring the leakage through the
cylinders caused by worn or damaged components. The operation of
the compression tester is based on the principle that for any given
airflow through a fixed orifice, a constant pressure drop across that
orifice will result.
The restrictor orifice dimensions for Continental aircraft
engines should be 0.040 inch orifice diameter, 0.250 inch long with a
60 degree approach angle. (See
~igure
7)
CYLINDER
PRESSURE
GUAGE
REGULATOR
PRESSURE GUAGE
AIR
VALVE
COMPRESSED
AIR SOURCE
CYLINDER
Figure 7. Schematic of Differential Pressure Tester
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