SIGMA 2
4
2.3 PNEUMATIC SYSTEM
The first stage pressure reducer has an
integral cylinder connector hand-wheel.
There is a sintered bronze particle filter in
the reducer inlet.
A high pressure PTCFE lined hose supplies
air to a shoulder mounted pressure gauge
and warning whistle.
The pressure gauge has a stainless steel
case and a polycarbonate, impact resistant,
splinter-proof lens. A blow-out vent prevents
over pressurisation of the case. A rubber
shroud provides mechanical protection.
The warning whistle operates at 55 bar.
Table 2 details the Warning Period for each
apparatus and cylinder combination.
If the hose, whistle or gauge become
damaged, a restrictor in the reducer body
limits air loss to 25 litres/minute.
2.4 REDUCER
The pressure reducer is a simple spring
and piston device that reduces the pressure
of air from the cylinder to a medium
pressure of between 5 and 9 bar. The
operation is automatic and self-regulating
such that the reducer requires no
adjustment.
In the unlikely event of a malfunction in the
reducer, resulting in an uncontrolled rise in
the output pressure, a pressure relief valve
protects the medium pressure system.
A reinforced hose supplies medium
pressure air to the DV.
2.5 DEMAND VALVE
SIGMA 2 is available with two types of
Demand Valve (DV):
• Instant air positive pressure DV (blue)
• First breath-activated DV (black).
Both types of DV have a supplementary
flow bypass and operate in conjunction with
the spring-loaded facemask exhalation
valve to maintain a positive pressure within
the facemask.
The DV senses the changes in facemask
air pressure that occur when the wearer
breathes; and uses this to regulate the
supply of air to the facemask. The DV is
attached to the facemask by a quick-fit
bayonet connection with a spring loaded
locking catch.
Instant Air Demand Valve
The instant air DV supplies air to the
facemask when the cylinder valve is
opened.
First Breath Demand Valve
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