3.4 Piping Schematic Component Index
Sample Isolation Valve
- This is a recommended item as it allows access to
the sample system without interrupting the main process line.
Filter Unit
– A filter unit is recommended when the samples are likely
to contain particulate matter. If the air/gas sample contains heavy
hydrocarbon condensate, the filter must be of the coalescing type with a
drain. The filter unit should be positioned as close to the sample point as
practical.
Sample Tube
– This should be stainless steel for dry air or gas applications
but copper or carbon steel can be used where wetter gases are to be
measured. If any section of the sample tube must be flexible then PTFE
should be used. In most cases, 3 mm OD (⅛”) is sufficient as it provides
good system response time with minimum flow. 6 mm OD (¼”) tube can
be used where pressure drops across the 3 mm tube are too high.
Pressure Reduction Valve or Pressure Regulator
– the sample is measured
at atmospheric pressure requiring that valve 4 is fitted to the system.
Flow Control Valve.
Sample Connection.
SDHmini.
Flow Indicator
– The recommended sample flow is 2 to 5 L/min.
Sample Exhaust
– The exhaust is vented to atmosphere or returned to an
atmospheric pressure line.
3.5 Purging the Sample Connection
Refer to the
Piping Installation Schematic
in section 3.3.
It is advisable to carry out an initial purge of the sample loop without connecting
the instrument, in order to avoid the possibility of sensor damage on start-up.
Open the sample isolation valve (1) slowly, until there is a small flow of air/gas at
atmospheric pressure from the pressure reduction valve (4). Allow the air/gas to
exhaust through the sample connection (9).
Continue this for two minutes to remove any residual moisture from the sample
pipe work and components. Check that no liquid or particulate contamination,
which could damage the sensor, is passing through the sample pipe. Directing the
sample onto a piece of white paper (such as a filter paper) will make it easier to
see any dust or oil mist in the sample.
1.
2.
3.
4.
5.
6.
7.
8.
9.
9
