USER MANUAL | ICOS | INSTRUCTIONS | UM/ICOS-EN REV. B.2
108
External Throttle Valve
The throttle valve reduces the pressure of the gas to the pressure controller, while the
pressure controller regulates the fine adjustments to maintain cell pressure. If the analyzer
is not operating at the target set point during high flow operation, the high flow throttle
valve may need to be adjusted.
The high-flow throttle valve:
Provides coarse manual control of the flow to compensate for various external inlet
configurations.
Optimizes the pressure at the target set point during high flow operation.
If the external throttle valve is closed, the flow is routed through the pressure controller.
(Figure 100) However, the pressure controller is not able to pass sufficient flow to the cell
at its target pressure in high flow mode. As the high-flow throttle valve is manually opened,
a point is reached where the flow through the valve combined with the flow through the
pressure controller is sufficient to maintain the target cell pressure. As the high-flow
throttle valve is opened further (approximately ½ turn), the electronic pressure controller is
within its control range and is able to throttle down its flow to compensate for the
additional flow through the valve.
The ideal operating point is for the high-flow throttle valve to be set in the middle of the
pressure control range. This midpoint can be set by slowly opening and closing the high-
flow throttle valve while observing the reported cell pressure and noting the points at
which the control range begins and ends. This control range typically spans approximately
½ turn of the high flow throttle valve. Once the range is found, set the valve position to the
middle of this range.
