Precision Medical HeliO2 Blenders - Manual (Page 7)

Heliox / Oxygen Blender Service Manual
Page 5
SECTION 2: TECHNICAL DESCRIPTION
The HELIO 2 Blender is a medical device used to mix Medical Heliox and USP Oxygen into a gas source ranging
from 20-100% or 30-100% Oxygen. The inlet gas connections are standard DISS or NIST for each gas. The inlets
are clearly marked and labeled on the bottom of the Blender. The outlets are standard DISS male Oxygen
connections.
The front panel of the Blender has a dial that is used to set the specific FIO2 blend. The dial settings range
from 20-100% on the PM5480 & PM5580 models and 30-100% on the PM5470 & PM5570 models.
The Path of the Gases
The supply enters through the Heliox and Oxygen inlet connectors located on the bottom of the Blender. Each
inlet connector contains a particulate filter and duckbill check valves which prevent possible reverse gas flow.
Diaphragm Housing Module
The two gases then enter the two-stage pressure Diaphragm Housing Module. In this module, the pressures of
both gas sources are equalized prior to entering the Proportioning Module. The pressure is equalized at the
lower pressure. The diaphragm within the module responds to the difference in pressure and directs the
movement of each check valve assembly contained within the Heliox and Oxygen chambers. The movement of
each ball adjusts the amount of gas flowing through the Diaphragm Housing Module, equalizing the Heliox and
Oxygen pressures to the lower pressure.
Proportioning Module
From the Diaphragm Housing Module the gases flow into the Proportioning Module and are mixed according
to the Oxygen percentage selected on the Oxygen Concentration Dial. The Proportioning Module consists of a
double ended valve positioned between two valve seats. One seat controls the passage of Heliox and the
other valve seat controls the passage of Oxygen into the outlet. At this point, the two gases have been
blended according to the Oxygen percentage selected on the Oxygen Concentration Dial.
With the Oxygen Concentration Dial at the full counterclockwise position (20/30%), the double ended valve
will completely close off the flow of Oxygen, allowing only the Heliox to flow. By adjusting the Oxygen
Concentration Dial to the full clockwise position (100%), the flow of Heliox is blocked, permitting only the flow
of Oxygen through the Blender outlet.
Alarm and Alarm Bypass
An audible alarm located on the bottom of the Blender signals when the difference in pressure between the
two inlet gases is ≥ 18 psi for Low Flow and ≥ 13 psi for High Flow. When the source gases are near equal
pressure, the alarm bypass poppet will remain seated over the alarm channel and the alarm does not sound.
When the gas pressures become unbalanced the higher pressure gas will unseat the poppet by overcoming
the spring force causing gas to flow through the alarm channel and the alarm sounds. The oxygen
concentration from the Blender will be that of the higher gas pressure. The Blender in the alarm/bypass mode
will deliver the oxygen (100%) or Heliox until the bypass mechanism resets when the source gas pressure is
restored to a differential of approximately 6 psi (0.42 kg/cm2). If the Blender is set at 20 or 30% (depending
on model), the OXYGEN source pressure is reduced or lost, the unit will not alarm because it will continue to
deliver 20 or 30% concentration according to the setting. If the control is moved slightly from the 20 or 30%
setting, the alarm will sound. Similarly, if the Blender is set to deliver 100% oxygen concentration and Heliox
source pressure is reduced or lost, the unit will not alarm because it will continue to deliver the selected 100%
concentration. The alarm will not function when there is no flow to the blender.