Figure 1-5. Electrical Schematic

TM 55-4920-335-14

Generator

13.

Indicator Light L.P. Filter

R.F. Connectors

14.

Indicator Light H.P. Filter

Shielded Leads

15.

Differential Switch L.P.

Voltage Regulator

16.

Differential Switch H.P.

By Pass Capacitor

17.

Fuel Level Switch

Fuse

18.

Fuel Level Gage

Ammeter

19.

Hydraulic Oil Level Gage

Battery

20.

Engine High Temp Switch

Start Solenoid

21.

Hydraulic Oil High Temp Switch

10.

Start Motor

22.

Magneto

11.

Start Motor Switch

23.

Spark Plugs

12.

Ignition Switch

Figure 1-5. Electrical Schematic

and then to the aircraft on test through one of the external

panel. The high pressure filter (21) incorporates a pressure

hoses provided. Fluid is then returned to the Test Stand

differential switch (22) connected across the filter. When the

through either the 1/2 inch (27) or the 3/4 inch (26) outlet,

differential exceeds 50 pounds, the switch will illuminate a light

depending upon the outlet selector valve setting, or through the

on the control panel indicating the fault. A case drain relief

one inch return fitting (28). High pressure relief valve (20)

valve (15) set at 15 psi is installed at the high pressure pump

regulates the system pressure, dumping the excess into the

case drain outlet to provide back pressure to the pump case

return line. Fluid may also be cycled through fluid bypass

drain line for lubricity purposes. The manifold (5) is connected

valve (29). Complete instrumentation is provided on the

in the suction line and houses thermoswitch (7) which

control panel to indicate hydraulic pressure (19), suction

energizes if hydraulic fluid temperature exceeds 71 degrees C

pressure (11), hydraulic reservoir level (2) and fluid

(160F) and opens the ignition circuit stopping the engine. The

temperature (6).

A differential pressure switch (9) is

low pressure relief valve (30) is mounted on manifold (5) and is

incorporated in the low pressure filter (8) and set to actuate

used to limit maximum pressure in the hydraulic system return

when a 40 pound drop occurs across the filter. This will be

line.

indicated by the illumination of an indicating light on the control

1-7