Figure 5-3.—Pressure-relief control valve.
relief for the fuel valve, and the other for the defuel
valve.
Each pressure-relief control valve contains a
stem, a diaphragm, a spring, and an adjusting screw.
Each valve is a direct acting, spring-loaded valve,
designed with a large diaphragm working area in
relation to the valve area seat, to ensure positive
operation. It is held closed by the force of the
compression spring. Pressure adjustment is made by
rotating the adjusting screw to vary spring
compression on the diaphragm. Compressing this
spring increases the pressure at which the valve
opens. The spring can be adjusted to provide a relief
setting from 20 to 70 psi. The adjusting screw is
covered by a protective housing.
When the controlling pressure under the dia-
phragm exceeds the set spring force, the disk is lifted
off the seat, permitting flow.
The pressure relief for the defuel valve is set
about 7 1/2 psi above delivery pressure. The pressure
relief for the fuel valve is set approximately 2 1/2 psi
above delivery pressure. The opening of the pressure
relief control valve for the fueling valve increases the
closing speed of the fueling valve. The opening of the
pressure relief control valve for the defueling valve
vents pressure from the bottom of the defuel valve
diaphragm, opening it.
Pressure-Reducing Control
Valve
The pressure-reducing control valve (fig. 5-4)
steadily reduces a higher initial pressure to a lower
pressure and regulates the delivery pressure when
the main valve is in the fueling mode.
The pressure-reducing control valve is a direct
acting, spring-loaded valve designed with a large dia-
phragm working area in relation to the valve seat to
ensure sensitive control and accurate regulation of
the delivery pressure. Pressure adjustment is made
by rotating the adjusting screw to vary spring
compression on the diaphragm. Compressing this
spring in-creases the delivery pressure setting. The
spring can be adjusted to provide delivery from 15 to
100 psi. The adjusting screw is also covered by a
protective housing.
The pressure-reducing control valve normally is
held open by the force of the compression spring.
When the delivery pressure acting upon the lower
side of the diaphragm exceeds the force of the
compression spring, the valve closes.
Conversely, when the delivery pressure reduces
below the spring setting, the valve opens. Thus, a
constant delivery pressure is maintained by
balancing delivery pressure against spring pressure.
The valve can be easily regulated by turning the
adjusting screw, which provides a simple means of
pressure adjustment.
Figure 5-4.—Pressure-reducing control valve.
5-3
