Is it meaningful to install pressure rings at multiple points on the pipe cross-section for pressure measurement?
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This post was last edited by Xin You Meng Hu on 2018-5-17 at 17:02. On some pipes larger than DN200, pressure measurement points are placed at three or more locations evenly distributed across the cross-section; a ring is then used to connect these points together, with a pressure transmitter or pitot tube attached to the top of the ring. It’s called a pressure ring. It is said to be for even pressure or something like that – does that make any sense? Is there any difference from measuring pressure directly at the top of the pipe? Does the pressure at the same cross-section within the pipe differ, and does it disappear once it is connected? Should we consider the impact of position difference on measurements for large diameters? I can’t figure it out; can someone explain it? P
The approach mentioned by the original poster is generally used in important flowmeters with low pressure differences; a pressure equalization ring is employed to connect the three pressure sampling points, thereby preventing pressure or differential pressure errors caused by differences in the sampling points, which could affect interlocks or indications. This structure is also commonly used in two-out-of-three pressure measurement systems, where three additional transmitters are connected to the pressure equalization ring to measure pressure and prevent discrepancies from causing interlocks or other issues.
This post was last edited by Xin You Meng Hu on 2018-5-18 09:20. Hello, as you said, I would like to ask further: what are the common reasons, from a mechanical perspective, for differences in pressure measurement points within the same cross-section of a pipe? Can a voltage equalizing ring resolve this difference? Is it caused by internal flow? Once it comes to rest outside the ring, it disappears; is then the static pressure equal to the static pressure inside the tube?
Firstly, the purpose of using a pressure equalizing ring is not to eliminate the factors that cause pressure differences, but rather to ensure that measurements are not affected by such differences; in other words, the pressure measured after equalization is as close as possible to the actual pressure inside the pipe. Second, there are many reasons for the different pressures at various locations inside the pipeline, such as the piping layout, foreign objects on the inner surface of the pipeline, and the flow conditions of the fluid. The main factors causing differences in pressure readings are related to the pressure sampling holes and tubes; for example, whether the sampling tubes extend a certain distance into the pipeline or not, or reach the inner surface, as well as roughness at the junctions where the sampling holes meet the pipeline due to welding.