2-36. Testing Radio Interference Suppression.
a. Place a radio receiver that is in good operating
condition in a position not more than 5 feet from the
tester. A wide band receiver with a frequency range
of 0.15 to 1000.0 megacycles is preferred.
b. Start the tester and tune the receiver in to
three widely separated frequencies at maximum
volume. Use frequencies that are free of signals
with strong carriers so that the receiver will be in
its most sensitive operating condition.
c. When the tester is operating, listen to the re-
ceiver for interference which ceases when the tester
is stopped and which indicates that the suppression
2-37. Replacement of Suppression Component.
(1) Disconnect plug from receptacle.
(2) Cut lockwire and remove from screws.
(3) Remove screws securing filter to electric
motor and remove filter and gasket from motor.
(1) Place gasket and filter in position on
motor and secure with screws.
(2) Secure the top two screws together and the
bottom two screws together with the lockwire.
(3) Install the plug on the receptacle.
2-38. General. The pump serves the dual func-
tion of developing pressure as well as vacuum for
operation of the tester. In the pressure section, a
mixture of air and oil is pumped into the reservoir
where the oil and air are separated. The separated
oil drops to the bottom of the reservoir where it is
fed to the pump for lubrication purposes, the air
being forced out at the top of the reservoir under
pressure. The pressurized air, after going through
the check valve whose function is to prevent oil
from entering instrument lines during operation,
enters an oil sump and passes through a filter which
is an integral part of the sump. Air from the sump
flows through two pressure control valves. The pres-
sure INCREASE valve controls the amount of air
permitted in the system and the pressure DE-
CREASE valve opens the line to the ambient air, al-
lowing system pressure to bleed off. The available
pressure level, as fixed by the control valves is sent
to the pressure relief valve and PRESSURE selector
valve. Setting the PRESSURE selector valve at the
desired test position completes the circuit to the in-
strument under test and simultaneously connects
the instrument under test and the master instru-
ment to one of the pressure relief valves. The pres-
sure relief valve is in the line at all times and pro-
tects the instruments from pressure overload when
the pump is producing vacuum which passes
through the check valve, and the sump which pre-
vents oil from entering the instrument lines. The
vacuum INCREASE valve controls the amount of
vacum in the system and the vacuum DECREASE
valve opens the line to the ambient air allowing the
system vacuum to bleed off. Setting the VACUUM
selector valve at the desired test position completes
the circuit to the instrument under test and the
master instrument to one of the three relief valves
which protect the instruments from vacuum over-
loads. The case leak valves provide isolation for the
master instruments of the test set to permit case
leak tests and/or calibration of the master instru-
ments without removing them from the tester.
2-39. Adjustment of Safety Relief System. All
instruments are protected by a safety relief system
which operates if excessive pressure or vacuum is
applied to any instrument. Five bellows assemblies
are used, two for vacuum and three for pressure (fig.
2-2). If excessive pressure or vacuum occurs, the ap-
plicable bellows actuate an associated microswitch
which in turn applies operating power to two sole-
noid valves. One valve is located in the pump pres-
sure line and one is located in the vacuum line.
When the valve operates, the pressure and return
lines close to isolate the instruments from the
pump. This safety relief system has been properly
set at the factory. In the event minor adjustment of
the safety relief system is required, proceed as fol-
a. Prepare test set for use in accordance with
procedure given in paragraph 2-25.
b. Release 10 captive fasteners and remove bot-
tom front panel of test-set to gain access to bellows
c. Place appropriate instrument under vacuum
or pressure, depending upon which bellows is to be
adjusted. Refer to paragraph 2-26 for operating pro-
cedure. Adjust the test set until instrument shows
d. Refer to figure 2-2 to identify bellows to be ad-
justed; markings on front of bellows block assembly
identify each bellows assembly and the instrument
system which it protects. Refer to table 2-1 for
safety relief point settings.