How to troubleshoot and maintain differential pressure flow meters?

As a flow measurement device widely used in industry and scientific research, the accuracy and reliability of differential pressure flow meters are crucial to ensuring the accuracy of production processes and experimental data. However, any mechanical equipment may encounter various faults and problems during long-term operation. Let’s learn how to effectively troubleshoot and maintain differential pressure flow meters.

1. The indication is too large or over traveled.

• Check whether the negative pressure valve or pipeline is leaking?

• Is there any foreign matter in front of the throttling piece? If the blowing is not clean, foreign matters would be blocked in front of the throttling piece.

• For differential pressure flow meters, the flow rate and the differential pressure are square root relations. Pay attention to whether the square root is repeated or not have been done. It is recommended to do the square root in DCS.

2. The indication is too small or returns to zero.

• Is the positive pressure valve or pipeline leaking? If the positive pressure side is blocked, the negative pressure unblocked indicator will  go below zero.

• Whether the balancing valve of the tri-valve set is closed.

• Check whether there is any leakage in the pipeline.

3. Error in steam measurement.

It is generally caused by the installation of the condensers. The function of the condenser is not only to condense high-temperature steam, but also to balance the positive and negative pressures. It is required that the height of the two condensers is consistent and the distance from the pressure point to the condenser should not be long. To avoid the formation of condensate in the pressure guide pipe, and to avoid the liquid levels are not be same.

4. Instruction deviation.

• Check whether the transmitter is set according to the data on the factory calculation sheet.

• Whether the gas measurement is compensated for temperature and pressure?  Or whether the flow unit is wrong?  Is it working condition volume flow rate or standard condition volume flow rate?

• Whether the calculated base density of the mixed gas is consistent with the base density of the process medium?

• If the change of expansion coefficient  in steam measurement deviates greatly, expansion coefficient compensation can be done.

• Whether it is measured in the small flow section of the design basis? The turndown ratio of orifice plate, nozzle, and venturi is 3:1. And the turndown ratio of  balance flow meter is 10:1.

5. Fluctuation.

• If the medium is liquid, check whether the pressure tapping is installed downwards. You can empty it to see if there are bubbles in the transmitter membrane box due to long-term operation. Similarly, if the medium is gas, the pressure tapping should be upward. And discharge the liquid generated.

• Increase transmitter / transducer damping.

• Whether there are fluctuations in the process measurement pipeline?

• If there is a flow control system, it can be achieved through PID adjustment.

• Note that the transmitter cannot measure stably when the pressure is less than 100Pa. Please check the differential pressure signal.

6. Errors caused by installation.

• Installed vertically if measure liquid, and the flow direction of the medium must be from bottom to top to ensure that the pipe is full when the liquid flowing through the throttling piece.

• When vertical installation, in order to avoid errors caused by liquid level differences in the pressure guide tube, the below pressure guide tube can be pulled upward for a short distance to keep aligned. Then no need any zero point correction.

• The condensers for steam measurement must be installed at the same level.