PRO-PAK
5
2.4 THE PNEUMATIC
SYSTEM
The pneumatic system has two pressure
reduction stages: air from the cylinder is
reduced to a medium-pressure (MP) of
between 5.5 and 11 bar by the reducer.
The second pressure reduction is
performed in the facemask Demand
Valve (DV).
Air from the cylinder passes through a
sintered bronze particle filter in the
cylinder connector, which protects the
pneumatic system, then through a short
length of high-pressure (HP) braided
hose to the reducer inlet manifold.
2.5 REDUCER
The reducer is a simple, self-regulating,
spring and piston device that requires no
adjustment. It has a pressure relief valve
(PRV) that protects the MP system from
over-pressurisation.
Air from the reducer is connected through
a reinforced, chlorinated polyethylene
hose to the facemask-mounted DV,
which regulates the air supplied to the
wearer.
2.6 GAUGE AND WHISTLE
A high-pressure hose from the reducer
inlet manifold connects air, at cylinder
pressure, to a warning whistle and
pressure gauge.
On standard versions, the warning
whistle and pressure gauge are mounted
on the left-hand shoulder strap. On
versions fitted with the
IRIS
data-
communications system, the warning
whistle and pressure gauge are
incorporated within the
IRIS
unit.
The warning whistle sounds when
pressure in the cylinder falls to 55 bar (
±
5
bar).
The duration of the air remaining in the
cylinder, from the start of the warning
whistle, is listed for each cylinder type
under
Warning Period
in
Table 3
.
The pressure gauge dial is photo
luminescent to aid use in low light levels.
The
lens
is
impact
resistant
polycarbonate. A rubber shroud protects
the gauge.
Should the gauge, whistle or hose
become damaged, a restrictor in the
reducer limits air-loss to less than 25
litres per minute.
2.7 DEMAND VALVE
The DV operates in conjunction with the
facemask spring loaded exhale valve to
maintain a positive pressure within the
facemask.
The DV has a servo-assisted tilting
diaphragm mechanism that responds to
pressure changes within the facemask to
regulate the flow of air to the mask,
ensuring that pressure within the mask
remains safely above ambient.
The DV has a reset button that enables
wearers to close the airflow through the
DV, permitting the facemask to be
removed during test procedures and at
the end of a task, without loss of cylinder
air.
When the apparatus is donned the DV is
normally ‘reset’ (closed), and is opened
(activated) when the wearer takes a first
breath.
