*TM 5-813-1/AFM-88-10, Vol. 1
operation. Where the supply is from wells, the quantity
(b) An indirect cross connection is
available in 48 hours of continuous operation of the wells
an arrangement whereby unsafe water, or other liquid,
will be used in calculating the total supply available for
may be blown, siphoned or otherwise diverted into a safe
replenishing storage and maintaining fire and domestic
water system. Such arrangements include unprotected
demands and industrial requirements that cannot be
potable water inlets in tanks, toilets, and lavatories that
curtailed.
can be submerged in unsafe water or other liquid. Under
(13) Peak domestic demand. For system
conditions of peak usage of potable water or potable
water shutoff for repairs, unsafe water or other liquid may
design purposes, the peak domestic demand is
backflow directly or be back-siphoned through the inlet
considered to be the greater of-
into the potable system. Indirect cross connections are
(a) Maximum day demand, i.e., 2.5
often termed "backflow connections" or "back-siphonage
times the required daily demand.
connections." An example is a direct potable water
(b) The fire flow plus fifty percent of
connection to a sewage pump for intermittent use for
the required daily demand.
(14) Fire flow. The required number of
flushing or priming. Cross connections for Air Force
facilities are defined in AFM 8521, Operations and
gal/min at a specified pressure at the site of the fire for a
Maintenance of Cross Connections Control and Backflow
specified period of time.
(15) Fire demand. The required rate of
Prevention Systems.
Ground water supply definitions.
The
b.
flow of water in gal/min during a specified fire period.
meanings of several terms used in relation to wells and
Fire demand includes fire flow plus 50 percent of the
ground waters are as follows:
required daily demand and, in addition, any industrial or
Specific capacity.
The specific
(1)
other demand that cannot be reduced during a fire
capacity of a well is its yield per foot of drawdown and is
period. The residual pressure is specified for either the
commonly expressed as gallons per minute per foot of
fire flow or essential industrial demand, whichever is
drawdown (gpm/ft).
higher. Fire demand must include flow required for
Vertical line shaft turbine pump. A
(2)
automatic sprinkler and standpipe operation, as well as
vertical line shaft turbine pump is a centrifugal pump,
direct hydrant flow demand, when the sprinklers are
usually having from 1 to 20 stages, used in wells. The
served directly by the water supply system.
(16) Rated capacity. The rated capacity of
pump is located at or near the pumping level of water in
the well, but is driven by an electric motor or internal
a supply line, intake structure, treatment plant or
combustion engine on the ground surface. Power is
pumping unit is the amount of water which can be
transmitted from the motor to the pump by a vertical
passed through the unit when it is operating under
drive shaft.
design conditions.
Submersible turbine pump.
(17) Cross connection.
A
(3)
Two types
submersible turbine pump is a centrifugal turbine pump
recognized are:
driven by an electric motor which can operate when
(a) A direct cross connection is a
submerged in water. The motor is usually located
physical connection between a supervised, potable water
directly below the pump intake in the same housing as
supply and an unsupervised supply of unknown quality.
the pump. Electric cables run from the ground surface
An example of a direct cross connection is a piping
down to the electric motor.
system connecting a raw water supply, used for industrial
fire fighting, to a municipal water system.
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