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Figure 2-1. Electrical Hook-up
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TM-55-4920-378-14-P Tester Pitot and Static System Manual
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PUMP.
Maintenance
TM 55-4920-378-14&P
SECTION III
MAINTENANCE
3-1.
GENERAL.
The basic principle of the tester is the use of a vacuum pressure pump, a series of instruments, connecting lines to selector valves
(Figure 1 - 1, Ref. 1 & 17) and control valves (2 & 3). The following procedures should be followed for maintenance of the test set.
3-2.
OIL RESERVOIR Maintenance of the reservoir consists of servicing as follows:
.
a. To fill the oil reservoir, open up the right side of the cabinet, unscrew the cap nut (14) next to the oil reservoir and adjust
the indicated handle (15) so that the handle points to the word "FILL". Attach the filler hose (Table 1-1, Item 1) to the threads
where you just removed the cap nut (14) and tighten securely. Place end of the filler hose in container of oil (MIL-H-5606).
b. With the valve in the "FILL" position, the hose in the oil, open valves (3), connect electricity to desired source and turn on
switch (4). You will note immediately the oil is sucked into the reservoir and you can control the amount of oil by turning off the
switch when the correct limit is reached. Then disconnect the filler hose, replace the cap nut (14) on the threads of the filler valve
and reset the indicating handle (15) to the "RUN" position. You are now ready for operation.
3-3.
SAFETY RELIEF VALVES.
All the instruments have been pre-set with the use of safety relief or overload valves (12 & 13). The safety relief valves have been
properly set at the factory to enable safe operation of these instruments even if overpressure is applied.* In the event adjustments to
the safety relief valves are needed, proceed as follows:
a. Place the instruments under pressure or vacuum, depending upon the desired instrument you wish checked, and slowly run
the instrument up to its maximum reading.
b. In the event that minor adjustments to the overload protection system are required open the lower front panel. The
overpressure safety relief valves (12 & 13) are identified for vacuum or pressure and the particular instrument system they protect.
Adjustment to the vacuum relief valves (12) require clockwise motion to decrease and counterclockwise motion to increase.
Adjustment to the pressure relief valves (13) require counterclockwise motion to decrease and clockwise motion to increase.
3-4.
INDICATORS.
The instruments are standard AN or MS type indicators and are stock units in the Army and can, therefore, be very readily replaced
by disconnecting the rear fitting hose and replacing the instrument. However, in the event the instrument is to be replaced, be sure
that the new instrument has a correct true calibration correction card with it or that these readings can be transferred to the Table
(10) on top of the tester for future use. Fuel pressure indicator and manifold pressure indicators gauges are no longer required in
testing aircraft components. Remove indicators, cap off airlines, stow electrical 'connectors and install cover plates over existing
holes.
3-5.
FUEL FILTER SUMPS.
The tester has also been equipped with two sumps which permit only the air to go into the instruments and, in the event there is oil
in the lines, it will be trapped in these sumps. You can readily see any trapped oil since the sump itself is clear glass. If the off after
months of operation gets to more than 500/0 of the total glass area, empty the sump and transfer the oil back into the reservoir. This
can be done by unscrewing the bottom of the sump, removing the sump and transferring oil to the reservoir. However, when
replacing the glass sump, be sure that it is securely tightened to prevent any possibility of leakage at this point. As soon as the sump
is replaced retest the unit for top vacuum, using the altimeter, and top pressure, using the fuel pressure. If you do not reach the top
point, it is because the gasket in the sump is not completely sealed. Tighten the bottom screw of the glass sump more.
*Does not apply to Rate of Climb - See Table 2-1.
Change 2
3-1

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