PERFORMANCE.

TM 55-4920-416-13

Section I

NAVAER 17-15C-539

Paragraphs 1-8 to 1-17

provided are used for the power sources specified, the motor is

1-8. PERFORMANCE.

automatically connected for proper operation. This feature

prevents connection of the test set to the wrong power source.

1-9. Table 1-2 lists supply requirements, performance data

and other leading particulars.

1-14. VACUUM AND PRESSURE SYSTEM (Figure 1 -5).

TABLE 1-2

1-15. The principal components of the vacuum-pressure

system are as follows:

PERFORMANCE DATA

a. A compact dual-purpose motor-pump assembly (1

and 2, figure 1-6). The motor section of the assembly is a

Type.......................................................Vacuum-Pressure Test Set

12,000 rpm, 1/30 horsepower, continuous duty, series wound

Model.......................................................................................VPT-7A

28 V dc motor. The pump section is a direct drive, positive

Power Requirements ...............................................28 V dc at 2.2A

displacement, rotary type pump with multiple porting.

115 V ac 1 ∅ 50-500 cps

b. An air-oil reservoir (3, figure 1-6), connected to the

115 V ac 3 ∅ 50-500 cps at 0.75A rms

pressure side of the pump, feeds filtered air under pressure to

Operating Temperatures ....................................... -40F to 150F

the pressure control valves (4, figure 1-7). The vacuum side of

(-40C to 65C)

the pump is connected to the vacuum control valves (3,

Max Pressure Produced ....................................................50 lb/in.2

figure 1-7).

Max Vacuum Produced.................................................-29.5 in. Hg

c. Two banks of relief valves (1 and 2, figure 1-7); three

Net Weight............................................................................57-1/2 lb

for vacuum and three for pressure. Their function is to protect

Shipping Weight Minus Overseas Packing............................67 lb

the master instruments (8, 9, 10, 11, 12, figure 4-1) and aircraft

Oil Sump Capacity..............................................................8 fluid oz.

instruments under test from excessive pressure or vacuum.

Dimensions

d. The vacuum and pressure selector valves (1 and 2,

Depth ..........................................................................14-1/32 in.

figure 4-1). These selector valves switch multiple pneumatic

Height...........................................................................14-3/4 in.

circuits. For each selector valve test position all necessary

Width ............................................................................16-1/2 in.

inlet and outlet, pressure and vacuum lines, control valves and

Storage Temperatures ......................................... -54C to 84C

instruments are properly connected.

(-65F to 183F)

e. A bank of simple plug valves (1, 2, 3, 4, 5, figure 4-2).

Pump Speed ................................................................. 12,000 RPM

These plug valves are located under the calibration card cover.

Rate-of-Climb Indicator ..................................0-6,000 ft/min (max)

They provide means for checking and calibrating master panel

climb or descent

instruments in the tester and are not used during routine

Altimeter Range.................................................. -1,000 to 80,000 ft

testing.

Airspeed Indicator Range .......................................... 50-650 knots

Manifold Pressure Indicator Range..............................10 to 75 in.

1-16. THEORY OF OPERATION (Refer to figure 1-5).

of Hg Absolute

Fuel Pressure Gauge Range .........................................0-25 lb/in.2

1-17. PRESSURE SECTION. The pump (1) serves the dual

Life .......................................................................................2,000 Hrs

function of developing pressure as well as vacuum for the

operation of the test set. In the pressure section a mixture of

1-10. DESCRIPTION OF THE MAJOR COMPONENTS.

air and oil is pumped into the reservoir (2) where the oil and air

are separated. The separated oil drops to the bottom of the

1-11. GENERAL. The VPT-7A is composed of a number of

reservoir where some is fed to the pump for lubrication

major components. These are grouped into two systems for

purposes, the air being forced out at the top of the reservoir

convenience and ease of analysis. They are as follows:

under pressure. The pressurized air, after going through a

a. Electrical system.

check-valve (3), whose function it is to prevent oil from entering

b. Vacuum system and pressure system.

instrument lines during transportation, enters an oil sump (4)

Minor components, not discussed in paragraphs 1-13 to 1-14

and passes through a filter which Is an integral part of the

are subordinate to one of these systems and are discussed at

sump. Air from the sump flows through two pressure control

an appropriate place in the handbook.

valves (5) and (6). The pressure increase valve (C3) controls

the amount of air permitted in the system. The pressure

1-12. ELECTRICAL SYSTEM (Figures 1-3 and 1-4).

decrease valve (6) opens the line to the outside ambient air

allowing system pressure to bleed off. Proper setting of these

1-13. The electrical system is designed for a wide range of

two valves enables the operator to maintain a pressure at any

power inputs. The tester will operate on 28 V dc or 115 V ac,

desired level within the limitations specified in Table 1-2. The

50 to 500 cycles, single phase or three phase line. Major

available pressure level, as fixed by the control valves, is sent

components of the system are a step-down transformer (1,

to the pressure relief valve PR-3 (10), and pressure selector

figure 1-3), selenium rectifier (2, figure 1-3) and an electrolytic

valve (7). Setting the pressure selector valve at the desired

capacitor (3, figure 1-3). The electrical system is energized

test position then completes the circuit to the instrument under

through a multi-pin AN connector (4, figure 1-3) and power

test and simultaneously connects the instrument under test

switch (7, figure 4-1). The internal connections of the power

and the master Instrument to one of pressure relief valves

cables and test set are such that when the special cables