How to calibrate the zero point of a differential flow meter
Thread Content
I’m in charge of process operations. I think that for a differential flow meter, the zero point can be calibrated by closing the inlet and outlet valves, but the instrument requires that the flow of fluid in the pipeline be stopped. The reason is that simply closing the inlet and outlet valves does not ensure that the pressure difference before and after the meter is zero; therefore, calibration of the zero point cannot be done accurately in this way. What he said makes a lot of sense; if the flow meter had a bypass line, I would have gone along with his suggestion. Unfortunately, it doesn’t have one. Moreover, the medium in question is feed for the furnace, and it’s impossible to stop its flow unless the operation is halted. What do you all think about this?
Close one valve – is there an exhaust loop? If there’s no bypass ring, then the flange has to be removed for calibration; resetting it will do. It’s not necessary to force the medium to be stationary and reset the atmosphere.
There is no vent ring; due to the high-temperature, high-pressure, and flammable nature of the medium, removing the flange poses certain risks
In your case, wait until the major repair to calibrate it!
The principle of the wedge flow meter is based on measuring differential pressure. To calibrate it, it is necessary to ensure that there is no differential pressure between the two flanges under identical conditions; you need to close the valve once, and since pressure is built up inside the diaphragm box, a pressure difference will definitely exist
Definitely not. After you close it, you can’t ensure that the pressures on both sides remain constant. Why can’t the flange be removed after the valve is closed? Unless there is a valve leak, if it’s necessary to calibrate the zero point regularly, a bypass should be added during major repairs. Sometimes, even after calibrating the zero point using atmospheric conditions, such flow meters still aren’t very accurate, as the process-related zero point varies slightly. The best approach is to calibrate the zero point after ensuring that no fluid is flowing in the pipes; this yields the most accurate results
There is no vent valve, and it’s uncertain whether the outlet valve can be closed tightly; if a leak is detected after removing the flange, it won’t be possible to tighten it again； It is difficult to carry out repairs with a bypass, as the flow meter is located above the pipe tray ； It seems that the only option is to install a vent valve during maintenance for easier calibration. I also have a question: is the zero-point calibration for double-flange level gauges based on the same principle, requiring a vent to be connected to the atmosphere as well?
Well, it’s exactly the same as what our instruments show
It’s the same principle, but it’s necessary to ensure that the two flanges are on the same horizontal level, or adjust the height of the capillary
The wedge flow meter can only be zeroed using a differential pressure transmitter. Smart transmitters allow for on-line zeroing, which can be performed via a smart handheld terminal. If that doesn’t work, it can be removed during maintenance for zero adjustment. Because you can’t guarantee that the valve will close completely in one attempt, and all other methods are unreliable.