Figure 12-25.--Typical thermal relief valve.
Motor-Operated Shutoff Valves
slide. The amount of rotation of the valve output shaft
is controlled by means of limit switches in the motor
The purpose of the shutoff valve, shown in figure
and gear assembly, which interrupt current to the
12-26, is to shut off the flow of hydraulic fluid to the
motor. When the valve is in the open position, the slide
is retracted into the valve body, thus permitting the
engine in case of an engine fire. The valve may also be
flow of hydraulic fluid through the valve. When the
used to great advantage during replacement of line
valve is in the closed position, the slide is positioned
quick-disconnects and other maintenance functions.
between the inlet and outlet ports, thus shutting off the
There are usually other shutoff valves, identical in
fluid flow.
appearance, installed within the same area that prevent
oil and fuel from reaching the engine in case of an
The valve incorporates a visual position indicator
engine fire.
(on the valve itself). The indicator is mechanically
connected to the operating parts of the valve and
When the shutoff valve is energized, an electrical
provides a positive indication of the position of the
impulse is applied to the electrical connector on the
valve.
motor, which converts the electrical energy into rotary
motion of the actuator output shaft by the means of a
CAUTION
gear train. This rotary motion is then transmitted to the
Operating an engine with the fire wall shutoff
shaft, which couples the actuator output shaft to the
valve closed could cause severe damage to the
crank assembly. The crank assembly then transmits
engine-driven pump.
the rotary motion of the shaft to the linear motion of the
12-24
