Automatic sprinklers - controls, gauges and alarms

Question 1

what is the main stop valve used for

Answer 1

The main stop valve
(MSV), fitted to all installations, enables water to
be cut off after the fire has been extinguished in
order to reduce water damage. It also permits any
actuated heads to be removed and replaced.

Question 2

list the general points regarding main stop valves

Answer 2

An MSV is of the gate valve type,
operates by hand-wheel and must be right-handed (i.e. must close by rotating clocwise )
The hand-wheel must be marked to show the direction of operation to close the valve
some indication given of whether it is open or shut. To prevent unauthorised interference and to guard against accidental closure,
MSVs are secured in the fully open position
with a strap, which can be cut in case of necessity.
They must be protected from frost.
The BS/LPC Rules require that a plan showing the
position of the MSVs must be placed within the
building where it can be seen easily by firefighters.
Where installations are arranged in zones, e.g. for
life safety, the plan must indicate the zone control
valves.
In addition a sprinkler location plate must
be fixed to an external wall as near to the MSV as
possible.
It must bear the legend (shown in Figure
4.1) in letters not less than 35mm in height, preferably in white on a black background.
Where possible the MSV must be placed close to
an entrance to the premises, preferably the main
entrance, in such a location as to be always readily
visible to authorized persons.
In addition to the MSV, each supply to the system
is fitted with a stop valve (see Figure 3.1).
Subsidiary stop valves may be used on certain sections of an installation to facilitate the testing of a dry-pipe valve, when a system is permanently on a
dry system or to control sprinklers on a tail-end
dry pipe system. The valves are of the interlocking
key type and when the valves are closed the key is
readily visible.

Question 3

describe a non return valve

Answer 3

The principle upon which a non-return valve
works is shown in detail in Figure 4.2. Water can
pass through the valve, only in the direction of the
arrows, by raising the clack valve. Any tendency to
cause a flow of water in the reverse direction
forces the clack valve on to its seating and so closes
the valve.

Question 4

when must a sprinkler system have a non return valve fitted to the supply

Answer 4

more than 1 supply.

Question 5

non return valves are fitted to prevent,,,

Answer 5

Non-return valves are fitted to prevent a reverse
flow in the supply system due to the unequal pressures
at which they operate. For example, if a town
main, having a good pressure, and an elevated tank
are used as water supplies to a sprinkler system,
water from the main would, unless a non-return
valve were fitted, pass up the supply connecting
the tank to the installation and cause it to overflow.

Question 6

describe drain valves and test valves

Answer 6

A pipe is led from the side of the alarm valve, in
wet installations, and from the air chamber of the
differential air valve, in dry or alternate systems,
into a drain. The pipe is fitted with a valve and the
pipe and valve are used to drain the system when
necessary and also carry out pressure and flow
tests. The diameter of the pipe will depend upon
the hazard rating of the occupancy.

Question 7

describe the pressure gauges and locations on a sprinkler system

Answer 7

Every sprinkler system must be fitted with a pressure
gauge (Figure 4.3(1)) above the alarm valve,
and this shows the pressure in the installation
(which will be water pressure when the system is
on water, and air pressure when on air). Another
gauge (2) must also be fitted below the alarm and
main stop valve, and this indicates the water supply
pressure

Question 8

pressure gauges must …..

Answer 8

There must be
means provided to enable each pressure gauge to be readily removed without interruption of installation
water supplies.

Question 9

The pressure indicated on the gauge (1) connected
above the alarm valve is sometimes higher than
that on gauge (2) below the main stop valve, why

Answer 9

This
is due to the fact that, after the system has been
charged with water, a rise in pressure in the town
main causes the alarm valve to lift and admit pressure
to the installation. When, however, the main’s
pressure falls again, the alarm valve retains the
pressure in the installation, which is, of course, a
non-return valve.

Question 10

The pressure indicated on the gauge (1) connected
above the alarm valve is sometimes higher than
that on gauge (2) below the main stop valve.. What can this cause

Answer 10

The difference in pressure sometimes results in a
slight delay in the sounding of the alarm gong.
When a sprinkler head opens, it is necessary for
the pressure in the installation to fall below that in
the main before the alarm valve opens and allows
water to flow to the water turbine of the alarm.

Question 11

Every installation must be fitted with an approved

water motor alarm . where should it be located

Answer 11

located as near the

alarm valve as practicable.

Question 12

how is the alarm valve activated

Answer 12

by a hammer rotated by a small pelton wheel
(more generally called a turbine) actuated as water
flows into the system.

Question 13

describe an alarm valve and pelton wheel

Answer 13

The alarm is sounded by a hammer rotated by a small pelton wheel
(more generally called a turbine) actuated as water
flows into the system. The pelton wheel is fitted
inside the building, and is connected by a spindle
hammer which, with the gong, is positioned outside
the building.
The gong is usually placed above and close to the
doorway that leads to the main stop valve. Where
more installations are fitted to that same building,
each has its own gong. Each gong must be numbered
in bold figures to correspond with the number
painted on the controlling valves of each
installation. The flow of water to the turbine may
also actuate an electric alarm at a central point and
so give immediate information as to the particular
installation that has operated

Question 14

There are four causes which may produce a ringing

of the alarm gong:

Answer 14

(i) The opening of a sprinkler head.
(ii) The opening of a drain or test valve,
(iii) Damage to any part of the installation, which
leads to an outflow of water.
A rise in the pressure of the water being supplied
to the installation, thus lifting the alarm
valve and allowing water to pass to the turbine
operating the gong.

Question 15

what precaution against false sprinkler alarms can be added to the system

Answer 15

As a precaution against false alarms caused by
spasmodic increases of pressure in the town main,
most alarm valves contain a small compensating
device which permits small quantities of water to
pass through the installation without lifting the
clack.

Question 16

In a wet pipe system, the gong may continue to

sound after testing, why

Answer 16

In a wet pipe system, the gong may continue to
sound after testing owing to an obstruction, such as
a piece of grit becoming lodged under the seat of
the alarm valve. Opening the drain valve fully will
probably cause the obstruction to be washed away;
if not, it may be necessary to close the main stop
valve, drain the installation, remove the valve
cover and thoroughly clean the alarm valve. The
gong may continue to sound if the alarm valve seat
has become scored or pitted so as to allow water to
flow continuously.

Question 17

Arrangements may be incorporated in the system
for the automatic transmission of alarm signals to
the fire brigade. Alarm signals may be initiated

Answer 17

(i) By a flow of water in the sprinkler system
using an electric alarm pressure switch connected
to the alarm valve in a similar manner
to the sprinkler alarm motor.
(ii) By using water flow alarm switches in the
system pipework above the alarm valve.
(iii) By a fall in pressure in the system pipework
above the alarm valve.