HELiOS Portables Technical Service Manual • PN 20562190 Rev E
10
HELiOS P
or
tables
Theory of Operation
V
Oxygen Delivery
The H300 & H850 are equipped with a pneumatic demand flow
control valve. Both have 12-position flow control knobs that
allow the user to select their prescribed flow rate for delivery.
The H300 has demand flow at a setting of 1.0 and above, and
continuous flow at all settings below 1.0 LPM. The H850 has
continuous flow (C) from 1-6LPM and demand (D) flow settings
from 1-4.
The pneumatic demand valve contains a series of chambers,
valves, and diaphragms that are shown below in Figure 9.
A dual lumen cannula provides the patient interface to the de-
mand valve. The lower cannula port on the H300 or H850 is re-
sponsible for detecting an inhalation, and the upper cannula port
is responsible for delivering the dose of oxygen.
Demand Flow
When a patient inhales on a demand (D) flow setting, a negative
pressure travels through the dual lumen cannula and the bottom
cannula barb on the H300 or H850. This pressure acts on the
bottom of the sensor diaphragm and combines with atmospheric
pressure acting on the top of the diaphragm to push it downward.
The lowering of the sensor diaphragm allows the pressure to
bleed from under the slave diaphragm out of the vent, causing
the slave diaphragm to push downward. This releases a stored
volume of oxygen in the precharge chambers and delivers it to
the patient through the upper cannula barb.
Figure 9:
Demand FCV Internal Diagram
CAUTION: A dual lumen cannula MUST be used on both
continuous and demand flow settings.
An initial volume of oxygen (called a bolus) is delivered imme-
diately when a patient breathes in. The amount of oxygen that is
delivered in this bolus is determined by the setting selected on
the FCV. After the initial bolus, a smaller volume of oxygen,
called a tail flow, is delivered continuously until the patient’s
inhalation stops. Figure 10 below is a graph showing the bolus
delivery of oxygen when the H300 or H850 is in demand (D)
mode.
When a patient stops inhaling, the sensor diaphragm raises up-
ward and blocks the bleed flow from under the slave diaphragm.
In turn, the slave diaphragm pushes upward and stops the tail
flow to the patient.
Demand Setting
Bolus Size (mL)
Tail Flow (LPM)
1
9.0
0.50
1.5
9.0
0.65
2
12.0
0.75
2.5
12.0
1.00
3
15.0
1.50
3.5
15.0
1.75
4
15.0
2.00
Table 2:
H300 Demand Flow Delivery
Table 3:
H850 Demand Flow Delivery
Demand Setting
Bolus Size (mL)
Tail Flow (LPM)
D1.5
9.0
0.65
D2
12.0
0.75
D2.5
12.0
1.00
D3
15.0
1.50
D4
15.0
2.00
Figure 10:
H300 & H850 Demand Delivery Curve
NOTE: Oxygen will only flow from the top cannula port. This
is normal behavior.
