Cressi MC9 Manuel D'instructions page 74

The adjustable nozzle is placed inside the valve seat. The outflow
air, when the mechanism is open, is directed through the injec-
tor and directly into the mouthpiece.
When the air flow inside the injector towards the mouthpiece
increases, it generates a vacuum inside the regulator' s case,
due to its acceleration. This vacuum, called Venturi effect flattens
the diaphragm, remarkably reducing the diver' s breathing effort.
The Venturi effect immediately stops as soon as the diver stops
breathing. The diaphragm returns to its normal position, the lever
comes up again pushed by its spring, and the nozzle is closed by
the piston.
To optimize the Venturi effect, XS2 CE is supplied with a flow
deflector with two operating modes, clearly shown by the scale
on the regulator housing:
pre-dive "-" and dive "+" (picture 20). In first mode, a flow limiting
device placed in the mouthpiece inlet starts operating and inhibits
the Venturi effect, preventing free flow. In "+" mode, the Venturi
effect works at its best, increasing the air flow supplied to the reg-
ulator to the maximum level.
WARNING: Always remember to set the flow deflector' s
lever in pre-dive (-) mode when not using the regulator;
otherwise, an accidental collision, the regulator falling into
water, pressing the manual regulation button without having
the mouthpiece in one' s mouth, or suddenly taking the regu-
lator out of the mouth might operate a strong free flow, cau-
sing high air consumption.
The dive (+) mode can only be used while diving and only
when the regulator is inside the mouth.
When the diver exhales, the pressure inside the regulator' s case
increases, opening the exhaust valve. This has been fully redesi-
gned and shows a larger diameter as well as a specially angled
conical shape, allowing air to flow outside. The exhaust tee
directs the air towards the head' s sides and protects the valve
from water turbulences which might lift it, when the inside is
depressurized, and flood it.
The 2nd stage is connected to one of the first stage' s 3/8"
ports by means of a flexible medium pressure and high capacity
hose.
All Cressi-sub second stages are downstream, that is the valve
automatically opens in case of calibration loss of first stage or of
a sudden intermediate pressure increase.
This means that any condition of over pressure upstream the
second stage leads to automatic free flow, never causing the
regulator to get stuck.
XS2 features a case in new techno-polymers with excellent
mechanic qualities and an attractive aggressive look. The main-
tenance is outstandingly easy and affordable, still easier on this
model thanks to a side tap, with its own O-Ring, for the valve
precise setting.
SECOND STAGES 57
fig. 20