There’s a strange issue that has arisen recently regarding orifice plate flow meters; I need help
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In our factory’s HCL synthesis furnace, orifice plates are used to measure the chlorine gas flow, with a differential pressure of 10 KPA. Later, due to requirements of the production process, this value was increased. However, there is a problem: the differential pressure read by the transmitter is now over 60 KPA. I’m not sure what the reason for this is; could it be that the pressure has increased? I hope colleagues can help me out – it’s urgent
Reply to 3# Wang Tianze: Please describe the issue more clearly – is the orifice plate in good condition, is there a problem with the transmitter, etc.?
Reply to 3# Wang Tianze: The differential pressure was set at 10 KPA during the design; the pipes didn’t change, only the pressure was increased
Reply to 4# LAN810: The orifice plate was removed and cleaned. At first, it was thought that there was a blockage on the negative pressure side; after cleaning it and reinstalling it, the problem persisted. Several different transmitters were tried, but the same issue occurred in each case.
As the gas flow rate increases, the pressure difference naturally increases as well. The simple relationship is dP~u^2. Take a look first before deciding.
Reply to 7# chemwanghq: I know, but it exceeds the scope of my original design. I originally designed the orifice plate for a differential pressure of 10 KPA, while now it can handle pressures of over 60 KPA.
In orifice plate calculations, density, orifice ratio, differential pressure, and flow coefficient are related to each other in a certain way. The medium density is generally calculated based on pressure, temperature, composition, and other factors. When temperature and pressure change, the expansion coefficient of the medium changes as well, and the expansion coefficient directly affects the differential pressure. A correction needs to be made at this time. Calculate the differential pressure based on the corrected value, and adjust the differential pressure accordingly. This is my personal understanding; please feel free to correct me.
This post was last edited by sdzbln on 2011-2-28 14:39. What is the pipeline pressure? Check whether the low-pressure valve of the three-valve assembly of the differential pressure transmitter is not open, or try opening the balance valve of the three-valve assembly first to see if the differential pressure value can be reduced. It seems that your differential pressure transmitter is only capable of measuring the pressure in the high-pressure section of the pipeline, and not the pressure in the low-pressure section. If possible, it would be advisable to try using a different differential pressure transmitter; if the problem persists, it might be due to a blockage in the three-valve assembly or the pressure lead pipes (the low pressure level could be extremely high). If only the pressure is increased, then the previously calculated differential pressure values need to be revised. Based on the orifice plate calculation sheet, by recalculating the differential pressure value without changing the orifice size, it is estimated that the problem can be resolved.
You’ve described the fault too vaguely. Generally, for this phenomenon: 1. First, you need to confirm whether, while increasing the flow rate, the process pipelines were also enlarged. If they were enlarged, their diameters will definitely be different, and the resulting pressure difference will also increase. 2. After you zero the gauge, check whether the instrument is functioning properly and whether the pressure transfer tube is unobstructed. It’s also similar to using a hand controller to check whether there is an instrument output current for the differential pressure reading. 3. For a differential pressure gauge used to measure flow rate, if you increase the flow rate, the range of the gauge will also increase. Check whether the increased range you have set has exceeded the maximum value of the instrument’s range.