Rising mains Flashcards
What is a rising main
A rising main (Figure 9.12) consists essentially of
a pipe installed vertically in a building with a fire
service inlet or town main connection at the lower
end and outlets at various levels throughout the
building.
Describe the outlet of a rising main
The outlet valves of these hydrants are usually
sealed with a wire and lead seal by the water authority
to prevent them from being used for purposes
other than firefighting. The outlets are mostly of the
wheel-operated type opening anti-clockwise; the
direction of opening, however, is always indicated
either on the wheel itself or on a plate fitted between
the wheel and the locking nut.
There are two types of rising main:
Wet
Dry
Describe a wet riser
A wet riser is a pipe permanently charged
with water,
any floor at which a hydrant outlet
(sometimes known as a landing valve) is provided.
The riser is connected to a town main of suitable capacity with a shut-off control valve
installed.
If the building height is such that the pressure in
the main is insufficient to supply four 13mm jets at
2.5 bar at the highest outlet, booster pumps are
necessary
Where these pumps are employed, the landing
valves must be fitted with a pressure regulator to
ensure that the pressure head against the pumps
(which can be in excess of 20 bar), is not transmitted to the hose.
A similar function to that of a wet riser is performed
by what is known as a ‘down-comer’. This,
like a wet riser, is constructed of vertical piping,
but is supplied with water from a tank in the roof
or at intermediate levels.
describe a dry riser
A dry riser is simply a vertical pipe, which is
normally kept empty of water, fitted with outlets at
various floor levels in the building. It is not
connected to a water supply, but is charged when
required by means of fire service pumps. In effect,
it is a substitute for a line of hose,
Advantages of a dry riser
Saves time
greater capacity than 70mm hose
Less risk of water damage
Roof outlets can help fighht fires in neighboring buildings
Describe the inlets to dry risers
Normally ground level
may be beneath ground below
pavement level in a box with a cover similar to that
used for a hydrant.
Where is the air valve fitted on a dry riser
at the highest level
Why is an air valve necessary
to allow contained air
to discharge to atmosphere when the riser is charged
with water. Without such a provision, air in the riser
might be compressed in the upper part of the pipe
and prevent it being fully charged.
What is advisable when opening the drain valve to empty the riser
When emptying a dry riser, it is advisable, if no
automatic air valve is fitted, to open the highest
outlet to admit air.
At what height are risers needed
20m dry or 10m beneath ground level
60m wet
in a wet riser when are booster pumps necessary
If the building height is such that the pressure in
the main is insufficient to supply four 13mm jets at
2.5 bar at the highest outlet, booster pumps are
necessary at suitable levels to ensure the maintenance
of the required pressure and flow.
In a wet riser with booster pumps what is also necessary and why
Where these pumps are employed, the landing
valves must be fitted with a pressure regulator to
ensure that the pressure head against the pumps
(which can be in excess of 20 bar), is not transmitted
to the hose.
Where are the outlets for risers found
firefighting staircase lobby
enclosed staircase forming part of an exit
All wet risers must have what added facility
All wet riser tanks must have a facility to allow the fire
brigade to replenish their contents. This is done by
installing an inlet breeching connection at a convenient
and safe location for the fire brigade to pump water
from the service main into the tank/s
