Automatic sprinklers.sprinkler heads Flashcards
There are many different designs of sprinkler head
but they may be generally divided into two categories:
(i) Those in which the operating medium is a
fusible solder,
(ii) Those in which a bulb is ruptured by the
expansion of a contained fluid
For normal occupancy situations, in temperate
countries, the recommended operating temperature
for sprinkler heads is
68 degrees c
describe the Fusible solder type
A head of this type is shown in Figure 5.2. The
deflector (1) is designed to spread the water issuing
from the orifice and is supported by the two
arms of the yoke (2). The yoke screws into the
body of the sprinkler which is itself, screwed into
the pipe. Held in place by the yoke is a flexible metal diaphragm (3) with a hole in the centre over
which fits a valve (4) of glass or gunmetal.
Over the valve is fitted a metal cap (5) which
contains a notch into which the end of the strut (6)
is inserted. The strut is supported by two other
metal plates: the hook (7), the curved end of
which engages the deflector end of the yoke, and
the key (8).
These three parts are held rigidly together by a
special fusible solder and keep the valve cap in
position against the pressure in the piping which
acts upon the other side of the diaphragm. When
the temperature surrounding the head rises to a
level at which the solder is heated to its fusing
point, the strut, hook and key fly apart owing to the
strain under which they are held. The valve cap is
released and allows the water an uninterrupted
passage to the deflector.
Under what conditions can sprinkler heads become uncertain
Sprinkler heads may become uncertain in
their operation if the normal ambient temperature
approaches too closely to operating temperature.
The temperature rating chosen should therefore be
as close as possible to, but not less than, 30°C
above the highest anticipated ambient temperature.
Ratings and colours of fusible metal
sprinkler heads
Rating of sprinkler in Degrees C 68/74 Natural 93/100 White 141 Blue 182 Yellow 227 Red Colour of yoke arm
how does a bulb type sprinkler head activate
In the bulb type head (Figure 5.5), a small barrel or
cylinder made of special glass is used to hold the
water valve in place. This bulb is hermetically
sealed and contains a quantity of liquid and a small
bubble. As the temperature rises, the liquid
expands and the size of the bubble decreases until
it disappears.
A further rise shatters the bulb, breaking it into
small pieces so that it cannot obstruct the water
flow, and so opens the head. In spite of this ease of
fracture, the strength of the bulb is such that it can
withstand any pressure applied to the pipe. In the
pressure destruction test, it is the metal parts of the
head that fail first.
The BS/LPC specify the following types of sprinkler
heads:
Conventional pattern n Spray pattern n Ceiling or flush pattern n Recessed pattern n Concealed pattern n Sidewall pattern
Describe the Conventional pattern of sprinkler head
This pattern produces a spherical type of discharge with a proportion of the water thrown upwards to the ceiling (see Figure 5.6). They may be installed upright (Figure 5.7(1)) or pendant
Describe Spray pattern sprinkler head
A hemispherical discharge below the plane of the
deflector is produced by this pattern with little or
no discharge upward to the ceiling. An upright
version is also availalable
Describe Ceiling or flush pattern sprinkler head
This pattern (Figure 5.7(3)) is for use with concealed
pipework. The heads are installed pendant
with the plate, or base, flush to the ceiling but with
the heat-sensitive element below the ceiling line.
They are also allowed to be installed in light or
ordinary light hazard areas.
Describe Recessed and concealed pattern sprinkler head
These patterns are similar to those described above
in Section 5.4.5. The concealed pattern however is
recessed almost level with the ceiling line and is
covered by a plate (Figure 5.8). In a fire situation
either the solder holding the plate in position melts
or bi-metal clips distort, allowing the plate to fall
away and expose the heat-sensitive element of the
head to the rising temperature.
describe sidewall pattern sprinkler head
This type (Figure 5.7(4)) is installed along the
walls of a room close to the ceiling. It produces a
discharge pattern resembling one quarter of a
sphere with a proportion discharging onto the wall
behind the sprinkler.
It can be used in positions where condensation
dripping from sprinkler pipework might be a problem
or, for aesthetic reasons or access problems,
where ceiling sprinklers are unacceptable.
Sidewall sprinklers should not be installed in High
Hazard areas above suspended ceiling
describe fast response sprinkler head
These are examples of recent developments.
Technology is constantly advancing and new system
designs being produced. Further reading of
appropriate new technical information will be necessary
to keep aware of such developments.
Normal sprinkler heads have fixed operating temperatures
and their design is such that they are usually
slower to react than electrical detectors. In
recent years certain hazards or types of premises
have required not only fast detection but fast control
and thought has turned to changing the design
of sprinkler heads to enable this to be done.
give three places a fast response sprinkler head may be used
Three diverse examples of areas where these types
of heads are desirable are high-bay warehouses,
residential care premises and private homes. In
these examples the amount of heat generated needs
to be sensed, retained and conveyed to the bulb or
soldered strut more quickly, either to avoid the
unusual rate of spread (high-bay warehouse) or to
save lives (residential premises).
