of normal limits. Figure 8-29 shows a typical high-
low water level supervisory device installed in a
sprinkler system reservoir.
A pressure-actuated level indicator is physi-
cally very similar to the bellows-operated pressure
switches used for water-flow detection (fig. 8-21).
As the water level changes in a reservoir, the water
pressure at the supervisory switch also changes.
The switch can be adjusted to actuate when
pressure indicates a low water level or a high water
level. This device is generally installed in the
piping near the bottom of the reservoir.
Electronic level indicators may also be found
in some systems. These indicators read the con-
ductivity of water to cause an electrical signal.
These devices are most frequently used to sense
high water levels. They are not commonly used
in fire protection systems.
Temperature supervisory devices are used to
prevent water freezing in fire protection systems.
Figure 8-29.Installation of water level and water
temperature supervisory devices.
Utilitiesmen will most commonly work with low
water temperature indicators. These are usually
sealed, factory-set thermostats and may be
installed in system pipe or reservoirs. The most
frequent low temperature setting is 40°F. Figure
8-29 shows a low water temperature indicator in-
stalled in a system reservoir.
You may find other supervisory devices in use.
They will usually be specifically designed for a
particular system. The principles of operation are
generally the same as those already discussed.
Physical mounting provisions or other details may
vary. Refer to NAVFAC MO-117, manufacturers
manuals, and NFPA #13 for more complete
information, when you must install or maintain
WATER SUPPLY REQUIREMENTS
Water supplies that serve sprinkler systems
must be adequate and reliable. To determine the
amount of water necessary for a sprinkler system,
the rate of flow and pressure needed for effec-
tive performance must be known. If additional
fire hose streams from outside the building will
be required, these should also be included. The
combined water needed for all fire-fighting equip-
ment is known as the fire flow demand.
An adequate system can deliver the required
fire flow for a specified time with normal water
consumption at the maximum rate. To be reliable,
the system must also be able to deliver the fire
flow demand under certain emergency conditions,
such as when a supply main or pump is out of
service. The desired reliability of the system
depends upon the nature of the protected struc-
ture (people, property, or mission). Water may
be supplied by public or base sources, water tanks,
or fire pumps.
For specific information regarding the fire
flow demands of sprinkler systems, refer to NFPA
#13, chapters 2, 7, and 8. These chapters will give
you the information required for the sizing of each
particular type of sprinkler system hazard based
on residual pressure, acceptable flow rates, and
INSPECTION, TESTING, AND
Sprinkler systems, when properly installed, are
an effective means of fire protection for life and
property. To make sure these systems are reliable,