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MOLBOX1+™/MOLBOX1+S, MOLBLOC TERMINAL OPERATION AND MAINTENANCE MANUAL
3.4.4.2
To purge the lines between the molbloc and the molbox1+ and the internal
molbox1+ volumes of one gas with another gas by setting up a molbox1+ valving
configuration in which gas flows through the molbox1+. Note that the purge
function is not supported by molbox1+S.
molbox1+ supports the measurement of flow of a variety of gases. To calculate the
flow, the thermodynamic characteristics of the gas must be known. These are stored
in molbox1+ memory. For the flow to be calculated correctly, the gas flowing through
the molbloc must be the gas that is selected on the molbox1+ (see Section 3.4.2).
When switching from the measurement of one gas to another, the old gas remaining
in the circuit and the new gas being flowed may mix for some time so that the gas
flowing through the molbloc is not purely the new gas. Erroneous measurements
may result. For this reason, it is important to purge the lines upstream and
downstream of the molbloc when changing gases. It is also important to purge the
molbox1+ itself which, since there is normally no flow through it, may trap and hold
the old gas.
The PURGE function is designed to facilitate purging the molbox1+. It sets up the
molbox1+ internal valving so that flow can pass through the molbox1+ (see Figure
7). In this configuration, the lines between the molbloc and molbox1+ and the
molbox1+ internal volume can be purged by simply flowing the new gas in the
normal flowing configuration. The flow resistance through the molbloc creates a
differential pressure which causes flow through the molbox1+ to occur, purging the
molbox1+ with the new gas.
© 1995 - 2010 Fluke Corporation, DH Instruments Division
<2Purge>
PURPOSE
PRINCIPAL
Internal Pneumatic Schematic – PURGING CHANNEL A
OPERATION
For best results, the PURGE function should be executed
whenever the species of the gas flowing through the molbloc is
changed. Prior to activating the PURGE function, set flow through
the molbloc to the highest rate that is practical. Then, with the gas
flowing, activate the PURGE function. Very small volumes of gas
remain trapped (deadended) in the molbox1+ in the PURGE
configuration.
Therefore, it may be desirable to execute the
PURGE function more than once to clear these volumes by the
pressure changes caused by PURGE execution.
Page 56
1. Channel A High Isolation: Open
2. Channel A Low Isolation: Open
3. Channel B High Isolation: Closed
4. Channel B Low Isolation: Closed
5. Bypass: Open
Figure 7. molbox1+
Note
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