1-19. FIREFIGHTING SYSTEM. - Continued
d. System Interlock Control - Structural Mode.
(1) In structural firefighting mode air, manifold # 2 is pressurized, (see fig. 1-40) and the circuit to the pump switch is
enabled via the closed contacts of pressure switch (B). The control circuit through valve switch (A) is by-passed thus
allowing the water tank valve to be open or closed as required. A diode between the switch (B) and the TANK VALVE
OPEN indicator prevents the indicator from being energized when the tank valve is closed.
(2) When the pump is switched ON, the PTO solenoid valve is energized. Pressurized oil from the transmission
engages the PTO clutch and triggers the oil pressure switch. This causes the PUMP ENGAGED indicator to illuminate.
The pressure switch (C) is open, triggered by air pressure in manifold # 2 (see para. 1-19 f.) and the throttle control
solenoid valve (L) is de-energized in this state automatic throttle governor control is locked out.
Figure 1-38. System Interlock Control
Change 6 1-45