FAMILIARIZATION AND CHECKOUT TESTS.

TM 55-4920-416-13

NAVAER 17-15C-539

Section IV

Paragraphs 4-25 to 4-34

opened, before starting tests. For oil draining and filling

apply when the values of the function

procedures see Section III, paragraphs 3-6 and 3-7.

(altitude, airspeed, absolute pressure) are

approached in an increasing direction.

4-25. To prepare the VPT-7A for operation, proceed as

This exercising will also provide a chance

follows:

to see if any excessive friction has

a. Remove the cover from test set.

developed in the instruments and will

b. Open lid of cover and remove the desired connecting

tend to reduce the friction on subsequent

cables. (Refer to Table 1-1 and figure 1-2 for identification of

test runs.

accessories.)

c. Connect proper cable to power connector and plug

CAUTION

into power supply.

d. Connect air hoses to instruments to be tested and to

If for any reason the relief valves open

the proper quick-connects at the rear of the test set.

during a test on any instrument, the test

e. Before energizing unit or proceeding with any tests

set shall be shut down and the readings

make sure that both VACUUM and PRESSURE selector

on all instruments be returned to normal

valves are set at OFF and the VACUUM and PRESSURE

before proceeding with that particular

control valves 1, 2, 3 and 4 are fully opened.

test. If relief valve relieves before top

f. Momentarily throw power switch to ON; indicator lamp

reading is reached see Table 6-1, Item 16.

should light, and pump motor should be operating. A quick

look inside the observation port in the right-hand door should

4-29. ALTIMETER AND RATE-OF-CLIMB. Procedures for

show oil circulating in the oil reservoir.

altitude and rate-of-climb tests are outlined in paragraphs 4-37

g. Throw power switch to OFF.

and 4-43.

4-30. AIRSPEED. Procedures for airspeed tests are outlined

CAUTION

in paragraphs 4-47 to 4-52.

During all operations and testing with the

4-31. MANIFOLD PRESSURE (VACUUM). Procedure for

VPT-7A make sure that the Vacuum and

manifold pressure (vacuum) test is outlined in paragraph 4-54.

Pressure selector valves are not moved

from their test position nor air lines

4-32. MANIFOLD PRESSURE (PRESSURE). Procedure for

disconnected while the pump motor is

manifold pressure (pressure) test is outlined In paragraph 4-59.

running or while any indication other than

zero can be observed on the instruments.

4-33. FUEL PRESSURE. Procedure for fuel pressure test is

(The indications will be zero on the rate-

outlined in paragraph 4-64.

of-climb indicator, local ground level on

the altimeter, 45 knots on the airspeed

4-34. TEST HOSE CONNECTIONS. The following steps

indicator, approximately 30 inches of Hg

illustrate the manner in which connections are made between

on the manifold pressure gauge, and zero

the VPT-7A test set and aircraft instruments to be tested.

on the fuel pressure gauge.) Failure to

When testing instruments in aircraft, disconnect the lines from

observe this will result in serious damage

the aircraft pitot tube at any convenient point.

to the master instruments on the test set

a. If it is desired to check out one particular instrument,

as well as to any external instruments

disconnect that instrument itself from the aircraft lines.

connected to the test set.

b. When testing altimeters and rate-of-climb indicators,

4-26. FAMILIARIZATION AND CHECKOUT TESTS.

connect to the instrument pitot-static line with one end of one

of the test hoses provided with the test set. Couple the other

4-27. GENERAL. The procedures given in paragraph 4-28

end of the hose to one of the quick-connect couplings with

through 4-32 are given to aid the operator in becoming familiar

needle valve, which is then snapped on to the ALTIMETER

with the operation and limitations of the VPT-7A test set. The

AND RATE OF CLIMB quick-connect nipple at the rear of the

tests described in the paragraphs noted above are performed

test set. Also connect, by means of the other test hose, quick-

with no external connections to the test set other than power.

connect coupling and needle valve, from the instrument pitot-

pressure line to the test set quick-connect nipple marked

4-28. EXERCISING INSTRUMENTS.

AIRSPEED.

c. For manifold pressure gauge tests use one of the

hose assemblies from the quick-connect nipple marked

CAUTION

MANIFOLD to the manifold pressure instrument line. Connect

from the test set at the FUEL PRESSURE nipple to any

Before making an accurate test it is

convenient point on the fuel pressure line when testing fuel

advisable to run the test instruments

pressure gauges.

through their complete ranges of

d. When checking instruments on the bench,

pressure or vacuum twice. This will

connections are made directly to the fittings on the instrument

normalize the small amount of hyteresis

cases.

in the diaphragms of the test instruments

so that the correction card errors will