Confusion regarding the installation location of pressure transmitters

Where is that provision? The description is inaccurate; it should be said that the pressure sampling point is located on one side of the medium, while the transmitter can be placed anywhere.

Many times, don’t get stuck on the outcome or strive to achieve it. From a different perspective, looking at the demands and reasons makes things much clearer. For gas media, the transmitter should be located above the pressure tapping point; of course, the pressure conduit must also have a slope to prevent the formation of liquid pockets. This facilitates the return of condensate back into the process pipeline, and it is this method that is recommended for installation. If the transmitter is located below the pressure tapping point, condensate will accumulate in the pressure tap pipe over time, which may affect the measurement or even render it impossible. Depending on the situation, it may be necessary to install condensate drainage measures at the bottom of the pressure tap pipe (or at the transmitter’s plug; generally, condensate is drained through the pressure tap pipe), with the method of drainage determined by the medium and operating conditions – either on-site or in a sealed manner. Liquid medium, the same principle applies. Additionally, the current version of HGT21581 is the 2012 version; the one released in 2010 was an informal version.

Those who can ask such questions are either beginners or those who have not applied theory to practice. First of all, the standard requirements state clearly that this is the recommended installation location; this location is determined by the condition of the medium, so no further explanation is needed on this point. If you look carefully at the installation manual, the older versions did not make any distinctions, but the newer version does provide such distinctions, with diagrams for pipe connections in non-recommended locations and diagrams for installation in recommended locations. As for why non-recommended locations arise, you’ll understand it if you’ve done any design work or been to the site. Theoretically, gas transmitters should be placed above the pipeline, but the pipeline might run along the ceiling – so where exactly should you place the transmitter? Your pipeline is 3 meters high – should you place the transmitter on the upper level or on the roof? Or have the piping team help you lower the pipeline? When measuring liquid pipelines, many of these pipelines are at relatively low levels; how should you position the transmitters? Lower than the low point? Look at it from the ground? Therefore, in engineering design, there are generally no absolute rules; decisions must be based on the actual circumstances. What is recommended is theoretical guidance only, and the final decision should be made according to the specific conditions on site, avoiding dogmatic mistakes.

Thank you all for your replies; I understand now. I used to work in the electrical field; I only switched to instrumentation later. There are many things I don’t understand, and I need to learn more*.

Floor 3 explained it in great detail. Installing the liquid at a 45-degree angle downward prevents the gas above the pipeline from affecting the measurements; a bubble rises up through it. How can it be measured accurately then? It is also best not to point vertically downward, to prevent debris or small particles from accumulating inside the pressure tapping tube.

Thank you. I have another beginner’s question: the pressure is taken from the upper part of the pipeline. Is this pressure measurement point located directly above the pipeline vertically? Should the pressure be taken at a 45-degree angle as well?

Look carefully at the picture album; it’s clearly marked.

The installation manual for version 2012 seems to no longer include installation methods where the transmitter is located below the pressure sampling point. When measuring the pressure of smoke gases, if the transmitter is below that point, condensation can occur easily, requiring frequent drainage. In northern regions, without heating, the transmitter can freeze over.

The 4th floor is the right choice! Installation is always carried out based on the actual circumstances! It’s not necessarily necessary to remove the condensate; just performing a zero-point shift is sufficient

This post was last edited by HEJIYUER on 2020-12-31 at 21:19. The principle regarding the relative elevation of the pressure conduit and the transmitter is to ensure that the medium inside the pressure conduit remains in a single phase, either liquid or gas, across varying ambient temperatures. This involves gas physical property parameters: what is the dew point of the medium under pressure? Compare it with the ambient temperature. 1. Dry gases, such as nitrogen/instrument air, have a very low dew point and do not produce condensation; therefore, the transmitters can be installed at various heights with ease. 2. Slightly condensed gases, such as compressed air or natural gas containing a small amount of heavier components, may precipitate liquid droplets at extremely low ambient temperatures, which continue to accumulate over time. A: Heat tracing, treated as a dry gas, installed on top. B: Fill with isolation fluid, treat it as a liquid, and install it below. 3. Thickable gases, such as water vapor, all gases that can be condensed by cooling water – their own condensate serves as the isolation fluid, which is placed at the bottom. (If the gas can be kept warm to maintain its gaseous state, it can also be installed above. But this is rarely done in practice) 4. A liquid that does not vaporize at ambient temperature, lower garment. 5. Liquids that are easily vaporized at ambient temperature, such as those used in air separation cryogenics, are actually gases inside the pressure guiding tube. (If a gas phase remains inside the tube at the lowest ambient temperature, it can also be installed in this way.) The most suitable approach is to use horizontal pressure taps; the transmitter and the pressure taps should be at the same elevation, and the pressure conduits should be laid horizontally and as short as possible, so that no liquid accumulation occurs. But opportunities are hard to come by. You can take a look at these HG installation diagrams as a reference, but specific issues need to be analyzed on a case-by-case basis; experience is the best teacher, so there’s no need to follow the instructions mechanically. For the attachment ISO-2186-2007 on the setup of the pressure guiding pipeline for differential flow meters, reference can be made to the study*.