Pressure tapping method for the throttling element
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For orifice plates, there are generally the flange pressure tapping method and the annular chamber pressure tapping method. How should one choose between these two? What are the advantages and disadvantages of each method compared to the other?
There are generally four methods for taking pressure readings using orifice plates: 1. Flange pressure tapping, 2. Annular chamber pressure tapping, 3. Radial distance pressure tapping, 4. Corner pressure tapping. The pressure tapping method is related to both the measured medium and the pressure level; it is necessary to determine the advantages and disadvantages of each option based on the actual operating conditions. The annular chamber is primarily designed to ensure accuracy and to provide pressure stabilization; it is suitable for measuring flows that require precise assessment. It is also necessary to take into account the medium and the diameter of the pipe – it is difficult to use an annular chamber when the pipe diameter is too small, while when the diameter is large, the edge effects on the flow are much reduced. Therefore, in cases of large diameters, pressure measurement can be carried out through drilling or using flanges.
Pressure tapping at the annular chamber is preferably not used when the medium is dirty, prone to precipitation, coking, or crystallization.
Flange sampling and corner joint (annular chamber) sampling are two common standard sampling methods. In the past, China used the corner joint sampling method (annular chamber sampling), but nowadays most cases employ the flange sampling method.
It is said that for orifice plates with a diameter greater than 400, flange-type pressure tapping is the best option, as it offers better cost-performance