Sampling System Design: Set Yourself Up for Success

Posted by Aubry Fielding on Feb 19, 2020 4:31:06 PM

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When designing a sampling system, even a minor miscalculation can lead to unreliable system operation. Now is the time to learn how to avoid classic liquid and gas sampling system mistakes. Below is a summary of a blog article posted by Karim Mahraz, Swagelok Product Manager, Analytical Instrumentation.

Temperature and pressure fluctuations cause gases to behave differently, and are common in sampling systems. These fluctuations can affect analyzer results by creating condensation or time delay. To avoid these types of issues, reduce a gas sample’s pressure as soon as possible and by as much as possible in order to reduce the sample’s temperature and minimize condensation and reduce heating needs down the line. Condensation is more likely on the high pressure side regulators and restrictors, like needle valves, capillary tubes or orifices.

What NOT to do when designing a gas sampling system

  • Transport Gas at its Dew Point Temperature 
  • Assume Insulation Will Keep a Gas Line Warm 
  • Have an Unheated Line Upstream of a Pressure Drop if you Heat the Downstream Side
  • Fail to heat a regular dropping more than 20 bars
  • Run Unheated Tubes in an Air-Conditioned Shelter When the Outside Lines are Heat Traced

Differing from gas samples, liquid samples necessitate a pressure increase for as long as possible. This is because when traveling through long tubes or flow restrictors, liquids drop pressure. Increasing pressure on the frontend helps move fluid through the system at a higher pressure and potentially reduces time delay as there will likely be no need for a downstream pump.

What NOT to do when designing a liquid sampling system: 

  • Transport a Liquid at its Bubble Point Temperature 
  • Drop Liquid Pressure at the Tap 
  • Install a Needle Valve before an Analyzer Flowmeter
  • Install a Needle Valve before a Vaporizer

Sampling system design is a delicate process that differs with every system. Swagelok Southeast Texas offers engineering services and hands-on sampling system training. Contact us for more information. 


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Topics: Training, Engineering Services, Grab Sample Systems