that for a hangar bay sprinkler system, start the pump at
through the distribution system or controls seawater
high speed. Low demand stations, such as that for a
flow on flight deck injection systems. The powertrol is
hose reel, start the pump at low speed. When the
held closed by spring pressure. The valve is actuated
system is being secured, you can only stop the pump at
when the control line is pressurized to firemain
the local control station.
pressure by the service solenoid-operated pilot valve
(SOPV). This control line pressure is exerted on the
AFFF Transfer Pumps
bottom of the diaphragm of the valve and the valve is
forced open against the spring.
The AFFF transfer pump is a permanently
VENT SCREW
mounted, single-speed, centrifugal type, electrically
WASHER
driven pump. These pumps are provided in 360-gpm
INDICATO R
STEM
capacity. The transfer pump moves AFFF concentrate
COVER
through the AFFF fill-and-transfer subsystem to all
AFFF station service tanks on a selective basis.
STEM
UPPER
DIAPHRAGM
WASHER
AFFF Tanks
DIAPHRAGM
POWERTROL
BODY
LOWER
AFFF is stored in service tanks of 50- to
DIAPHRAGM
W ASHER
2,000-gallon capacity and storage/transfer tanks of up
to 3,500-gallon capacity. The tanks are rectangular or
cylindrical in shape and are fabricated out of
O-RING
RETAINER
BEARING
90/10 copper-nickel or corrosion-resistant steel. Each
FLOW
service tank is located inside the AFFF station and is
DISK
SEAT
fitted with a gooseneck vent, drain connection, fill
connection, liquid level indicator, recirculating line,
and an access manhole for tank maintenance. The
BODY
gooseneck vent prevents excess buildup of pressure
DCf0608
within the tank during storage and prevents a vacuum
Figure 6-8. Powertrol valve.
when the system is in operation.
AFFF Valves
POWERCHECK VALVE.-- The powercheck
valve (fig. 6-9) is a diaphragm type, normally closed,
The AFFF system requires a variety of valves with
seawater pressure-operated control valve. This valve
d i ff e r e n t f u n c t i o n s . T h e s e va l ve s i n c l u d e t h e
allows flow of AFFF from the pump to be mixed with
following:
seawater, and protects the AFFF tank from seawater
Powertrol valve
c o n t a m i n a t i o n o r d i l u t i o n . T h e p ow e r c h e c k i s
Powercheck valve
essentially a powertrol valve that has a lift-check
feature built into it. When there is no pressure on the
Powertrol valve with test connection
control line, the upper valve spring forces the valve
Hytrol valve
closed and the lift check feature is inoperative. When
there is firemain pressure on the control line, this
Hycheck valve
pressure acts on the bottom of the diaphragm and
opens the valve against the upper valve spring. AFFF
Balancing valve
flow pushes the disk and lower stem up and allows
AFFF to flow. If the back pressure downstream of the
Balanced pressure proportioner (Type II)
valve exceeds the pressure on the upstream side of the
Balanced pressure proportioner (Type III)
valve, the valve disc holder and stem will slide to the
CLOSED position, preventing any backflow through
POWERTROL VALVE.-- The powertrol valve
the valve. On balanced pressure proportioning
shown in figure 6-8 is a diaphragm type, normally
systems, the powercheck does not have a lower
closed, seawater pressure-operated control valve. This
spring.
valve allows the flow of AFFF/seawater solution
6-7