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Measuring The Pressure Of High Temperature Media

In many fluid power applications, the medium that the instrument will contact may be at an elevated temperature beyond the operational limit of the measuring instrument. Selecting an instrument with a high temperature rating or using diaphragm seals to provide isolation from the medium may not be feasible from a design or economic standpoint.

One way to address this situation is to mount the instrument with a short length of tubing away from the hot area where the measurement needs to be made. With a dead ended pressure chamber, the tubing will effectively dissipate much of the heat and bring the medium in contact with the measuring instrument down to a lower temperature that is within its safe and accurate limit.

The following chart provides the basic information needed to determine the size and material of the tubing needed.

These curves are based upon the following assumptions:

  1. The pressure vessel is insulated to limit radiant heat transfer to the transducer – the major source of thermal input is via the connecting tube.
  2. The pressure medium has a coefficient of thermal conductivity less than 4btu / hr / ft2 / ft / °F. This figure encompasses a wide range of liquids and gases.