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  TM 55-4920-231-14
(7) Remove test hoses and external case
or in the aircraft by disconnecting the line to
leak valves (10, figure 4) from tester and install
the instrument and accomplishing the following:
(1) Remove cap (4, figure 4) and install
caps (4) on fittings.
external case leak valve (10) on fitting indicated
(8) Stow all accessories neatly and compact-
for instrument being tested (figure 4). All other
ly in cover compartment (2, figure 3).
caps must be on fittings.
(2) Connect hose assembly (5 or 6, figure
3) to external case leak valve (10, figure 4) and
Perform the following relief and leak tests on
to fitting on instrument being tested.
master instruments before testing aircraft instru-
(3) When the tests have been completed,
ments to ensure the accuracy of the readings and
disconnect the test hose from the instrument.
to normalize the slight amount of hysteresis in
WARNING
the diaphragms of the test instruments. This will
Secure all connections to prevent leak-
provide for observing any excessive friction de-
age or loosening due to vibration.
veloping in the instruments and will tend to re-
duce the friction on subsequent test runs. Install
(4) Install all lines and secure all connec-
cap (4, figure 4) on fitting (3, 5, 6, and, 7)
tions which were removed for the tests.
and tighten.
(5) Remove test hose and external case leak
valve (10, figure 4) from tester and install cap
CAUTION
(4) on fitting.
The airspeed indicator must be isolated
(6) Stow all accessories neatly and com-
from the vacuum source to prevent dam-
pactly in cover compartment (2, figure 3).
age to instrument.
CAUTION
The case leak valve must be in CL posi-
(1) Remove cap (4, figure 4) from R.O.C.
tion and the safety valve closed to iso-
--ALTIMETER fitting (7) and install external
late the airspeed indicator from the vac-
case leak valve (10).
uum source to prevent damage to the
(2) Connect hose assembly (5 or 6, figure
instrument.
3) to valve and to pitot static connection.
(3) Place case leak valve lever (4, figure 8)
(3) Remove cap (4, figure 4) from AIR-
in CL positions and turn knob (14, figure 4)
SPEED fitting (6) and install external case leak
to close safety valve (13 ).
valve (10).
(4) Place case leak valve levers (3, 5, 7,
(4) Connect hose assembly (5 or 6, figure
and 8, figure 8) in NOR position.
3) to valve and to pitot pressure connection. The
unions (15 and 16) are provided to make the
(5) Wart the tester (paragraph 36).
necessary connections.
CAUTION
(5) When tests have been completed, dis-
Do not exceed a rate of change in alti-
connect all test hoses and remove all test equip-
tude of +3,000 fpm while testing altim-
ment from aircraft.
eters as damage to the altimeter may re-
sult. Do not exceed +6,000 fpm during
these tests as it will damage the rate-of-
climb indicator.
(6) Slowly turn vacuum INCREASE knob
(17, figure 7) to open valve and provide a read-
(6) Install all lines and secure all conne-
ing of 5,000 fpm on rate-of-climb indicator (2).
tions which were removed for the tests.
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