6.5 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 (1/8”) is sufficient as it provides good system response
time within minimum flow. 6 mm OD (1/4”) tube can be used where pressure
drops across the 3 mm tube are too high.
Pressure Reduction Valve or Pressure Regulator
– If the sample is to be
measured at atmospheric pressure then the valve 4A should be fitted and
4B omitted from the system. If the sample is to be measured, at full line
pressure and the exhaust vented to atmosphere, then valve 4B should be
fitted and 4A omitted from the system. If measurements are to be taken at
full line pressure and the sample is to be returned to a part of the main line
or a vent, which is at a pressure higher than atmospheric and the input to
that line needs a controlled pressure then both 4A and 4B will be required.
Sample Pressure Gauge
– This is not a critical part of the moisture
measurement but may be required if dew point/ frost point measurements
are to be made at higher than atmospheric pressure.
Measuring Transmitter
, see “Section 19 – Transmitter Diagram”.
Transmitter Holder
, see “Section 20 – Sensor Holder Diagram”.
Desiccant Chamber
– This item is required when the sampling is to be
intermittent. When installed, it prevents the ingress of wet air to the sample
system while the sample is not flowing, improving the response time.
Flow Control Valve
– This can be a separate item or combined with the flow
indicator.
Flow Indicator
– The recommended sample flow is 2-5 litres/min.
Sample Exhaust
– The exhaust can be vented to atmosphere or returned to
the process line as discussed above.
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