Service manual

30 Infant Flow
®
SiPAP
675-120 Revision D May 2005
Chapter 5 - Operation
Gas Flow
With the oxygen and air connections connected and the power switched on, oxygen
and air at 386 kPa (56 psig) flows to the blender. The air passes through a water trap
with an integral filter where any moisture in the air is removed. Oxygen and air are
filtered before entering a non-return valve in the blender. The blender mixes the
oxygen and air in the proportion set by the position of the FiO
2
control valve. The
blender supplies blended gas between 2.5 and 30 L/min.
The blender incorporates an alarm/bypass module. If a single gas supply fails or
there is an imbalance between the inlet gas pressures exceeding 200 kPa (30 psig),
the module directs the flow through a reed whistle to warn the Operator of the
condition and at the same time connects the inlet gas at the higher pressure to the
blender outlet.
The blended gas is filtered before passing through a flow control to an oxygen
analyzer. The oxygen analyzer utilizes a galvanic fuel cell to measure and display
the measured delivered oxygen concentration.
A vent valve on the exhaust manifold incorporates a solenoid operated pilot valve
and a large orifice spool valve. The vent valve is normally held in the open position
by a spring to vent high flow rates with low pressure drops so that the patient
pressure is minimal. The electrically actuated pilot valve is operated by blended gas
so that the vent valve continues to operate if one gas supply is lost.
Blended gas flows through an electronically operated dump valve which is normally
in the closed position. If over pressurization occurs, the sensors detect the condition
and the controller signals the dump valve to open, sounds an alarm buzzer and at
the same time closes the vent valve to rapidly reduce the patient pressure to near
zero. When the over pressure condition stops, the controller signals the vent valve to
open and the dump valve to close.
The NCPAP flowmeter is set by the Operator to the required flow. The flow rate is
shown on the gauge on the flowmeter. When the flowmeter control knob is turned
fully clockwise, the flow of gas is turned off.