MIL-HDBK-1022A
position. The system is controlled by two redundant PLCs and
is constantly pressurized when in operation. Fuel is pumped
from the tanks, through filter separators and a supply venturi
into the hydrant loop. It flows through the appropriate
hydrant valve, through a hydrant servicing vehicle or mobile
pantograph, into the aircraft if refueling is underway. A
backpressure control valve keeps system pressure at a pre-set
level and a return venturi measures flow back to the storage
tank. Working in conjunction with the return venturi, pumps
are turned on and off depending on refueling requirements.
This system is sized in 600 gpm (38 L/s) increments up to
2,400 gpm (152 L/s). Issue pumps are sized to provide a
minimum of 100 psi (690 kPa) at the outlet of the most distant
hydrant adapter. Each hydrant pit control valve is equipped
with a pressure control and surge shutdown pilot. These pilot
controls are set at 45 psig (310 kPa) and 50 psig (345 kPa),
respectively. The hydrant control valves allow flow rates up
to 600 gpm (38 L/s) using a 4-inch valve and flow rates up to
1200 gpm (76 L/s) using a 6-inch valve. Contact Service
Headquarters for specific guidance and sizing of the hydrant
control valve. Refer to Standard Design AW 78-24-28 for Type
III hydrant systems.
4.4.2.4
Helicopters. Use the following design criteria for
direct fueling systems for helicopters:
a) Design piping, pumps, controls, accessories, and
auxiliary systems in accordance with other applicable
paragraphs of this section. For each direct fueling station,
provide a nominal maximum flow of 300 gpm (19 L/s). Design
system to be capable of delivering 275 gpm (17 L/s) at 35 psig
(240 kPa) nozzle pressure. Make the minimum size system 600
gpm (38 L/s) with at least two fueling stations. For
diversity usage, increase by 300 gpm (19 L/s) for every three
additional fueling stations. At outlying fields and with
Service Headquarters' approval, a single fueling station may
be used.
b) Provide aboveground direct fueling stations
equipped identical to fixed-wing small-frame aircraft fueling
stations. Design the horizontal position and vertical
projection of fueling equipment to avoid interference with the
helicopters' blades when in the drooped attitude.
c) Coordinate type of pressure nozzle with user.
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