Sample Conditioning System
Hardware Installation and Maintenance Manual 4
–11
1. Isolate the analyzer from the bypass following the procedure under
“To isolate the measurement sample cell for short-term
shutdown” on page 4-10.
2. Close the sample supply shut-off valve to the SCS.
3. Allow the sample bypass to flow until all residual gas has dissipated
from the lines as indicated by no flow on the sample bypass
flowmeter.
4. Close the low pressure flare or atmospheric vent header shut-off
valve for the effluent from the sample bypass.
5. Turn off power to the analyzer.
Toisolatetheprocesssampletapforlong‐termshutdown
If the SCS is to be out of service for an extended period, the SCS must be
isolated at the process sample tap.
Although the pressure reducing regulator at the process sample
tap is designed for “bubble-tight” shut off, this condition may not
occur after the system has been in operation for an extended
period. Isolation of the SCS from the field pressure regulator will
discontinue sample flow and may cause the pressure at the outlet
of the field pressure regulator to slowly increase if “bubble-tight”
shut off of the pressure regulator does not occur. The slow
pressure increase will continue until the pressure setpoint of the
relief valve is reached and the excess pressure is vented by the
relief valve. To prevent this, isolate the sample at the probe or
vent the sample to a safe location.
If the system will not be out of service for an extended period,
SpectraSensors advises that power remain applied to the sample
transport line electric tracer and the sample system enclosure
heater, if applicable.
The process sample at the sample tap may be at a high pressure.
A pressure reducing regulator is located at the sample tap to
reduce the sample pressure and allow operation of the SCS at a
low pressure. Use extreme caution when operating the sample
probe isolation valve and field pressure reducing regulator.
The sample transport line must be vented to the low pressure
flare or atmospheric vent header through the bypass flowmeter to
avoid pressure surges. The procedure given in the following steps
can be followed regardless of whether or not the SCS has been
isolated from the process tap as described in the previous section.
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