contained within gas cylinders is initially very high and falls
as the contents are used. The function of the regulator, or reducing
valve, is to convert this variable, high-pressure gas supply to
a constant, low-pressure gas supply of around 50 psi.
using a regulated, low pressure system in an anesthetic machine
is easier and safer to manufacture the pipework in the machine
using low-pressure piping and connectors, and the consequences
of a gas leak are less serious.
eliminates the necessity of constantly adjusting the flowmeters
as the pressure in the cylinder falls.
enables better control of the gas flow to be maintained: since
the needle-valve and flowmeters are larger for a given flow
rate, they are less prone to inaccuracy due to wear or the presence
As gas flows
out of the low-pressure chamber, the drop in pressure reduces
the force generated by the diaphragm (D) against the spring (S),
allowing the valve (V) to open and admit gas from the high-pressure
chamber. The output pressure may be adjusted by a screw (A) that
alters the force applied by the spring.
The regulated low pressure will only remain constant over a certain
range of pressures in the cylinder. If the contents of the cylinder
are used to the point of exhaustion, the pressure in the low-pressure
system will fall. This may present a hazard if, to compensate
for this, the flow control is further opened and, later, a full
cylinder is connected to the system. The high pressure in the
new cylinder will now generate a very high flow into the breathing
circuit which may result in a rapid increase in pressure and barotrauma
to the lungs.
Two-stage regulators essentially consist of two single-stage
regulators mounted in series, so that the low-pressure chamber of
the first stage becomes the high-pressure chamber for the second
stage. Since the pressure in the intermediate chamber is relatively
constant, this arrangement provides very precise control of the
pressure in the final chamber. Two-stage regulators are relatively
expensive and so are only used in situations where it is important
to maintain the output pressure within close tolerances.
Some oxygen regulators incorporate a Bourdon-type flowmeter and
flow restrictor, and are intended for delivery of oxygen directly
not be used to supply oxygen to the anesthetic machine since the
limited flow (typically 8 or 15 l/min) will be inadequate to operate
the quick-flush or ventilator.