Demand and dilution mask regulator and method of regulating additional oxygen in the mask regulator
A demand and dilution mask regulator comprising an oxygen feed circuit and a dilution circuit for supplying air. The oxygen feed circuit and the dilution circuit are connected to a mixing chamber ( 35 ). In the dilution circuit, the inhaled breathe-in air flow rate is measured through a capillary duct ( 43 ) connected to a Venturi construction ( 41 ). A method of regulating the flow rate of additional oxygen uses flow rate data measured through the capillary duct ( 43 ) for controlling the oxygen flow rate to be supplied to the mixing chamber ( 35 ).
1. A demand and dilution mask regulator comprising:
an oxygen feed circuit connecting, through a first flow path, a pressurized inlet for oxygen coming from an oxygen source and admitted into a mixing chamber leading to a breathing mask, via an electrically-controlled valve for controlling the oxygen flow rate,
a dilution circuit supplying air, through a second flow path, from an inlet connected to an air source, to an outlet leading to the mixing chamber, characterized in that the second flow path comprises a Venturi constriction and a capillary duct having an inlet port connected to the Venturi constriction and an outlet port connected to a pressure sensor.
2. A regulator according to claim 1 , wherein the capillary duct has a diameter comprised between 0.1 and 0.4-mm.
3. A regulator according to claim 1 , wherein the Venturi constriction has a section of essentially 0.57 mm 2 .
4. A regulator according to claim 1 , wherein the inlet port of the capillary duct is located upstream of the mixing chamber.
5. A protective breathing equipment with a mask comprising a regulator according to claim 1 and a mask storage box comprising an electronic control circuit and the pressure sensor, the capillary duct, electric wires and an oxygen duct extending from the mask storage box to the regulator.
6. A method of regulating a flow rate of additional oxygen taken from a pressurized inlet for oxygen coming from a source and admitted, through a first flow path, into a mixing chamber leading to a breathing mask, via an electrically-controlled valve for controlling the oxygen flow rate, the method comprising supplying air, through a second flow path, from an inlet connected to an air source, to an outlet leading to the mixing chamber,
the method being characterized in that it further comprises:
measuring the air pressure in the second flow path at a Venturi constriction, through a capillary duct having an inlet port connected to the Venturi constriction and an outlet port connected to a pressure sensor, and
using data from the pressure sensor for controlling the oxygen flow rate delivered through the electrically-controlled valve.
7. A method according to claim 6 , wherein the oxygen flow rate delivered through the electrically-controlled valve is given by:
Q
ATPD
=
K
T
P
A
Δ
P
where
ΔP is the pressure measured by the pressure sensor connected to the capillary duct,
P A is a pressure measured in the ambient atmosphere,
T is the temperature in Kelvin, and
K is a constant adjusted according to altitude rate.