1、 Selection of sensors for turbine flow meters

1. Suitable for measuring fluids: Turbine flow sensors are suitable for measuring clean (or essentially clean) low viscosity single-phase fluids (gases or liquids), such as water, light oil, petroleum solvents, acids, bases, liquid oxygen, liquid nitrogen, liquid hydrogen, and air, oxygen, etc. If measuring high viscosity liquids, the impact of viscosity on sensor performance will reduce measurement accuracy. If measuring liquids mixed with solid particles, turbine flow meters are not suitable for use due to their susceptibility to bearing damage. When measuring highly corrosive liquids, it will cause difficulties in selecting materials for major components such as impellers, and their corrosion resistance has certain limitations, so careful selection is necessary. Gas measurement is appropriate, but due to the low gas density and high flow rate, special considerations must be made for the design of structural parameters. It is generally not suitable for measuring gas-liquid mixed flow and steam.

2. Selection of caliber: Each caliber sensor has a certain flow measurement range. The selection of sensor aperture is generally determined by the flow range, that is, the * small flow rate during use shall not be lower than the * small flow rate allowed to be measured by the aperture, and the * large flow rate during use shall not be higher than the * large flow rate allowed to be measured by the aperture. From the perspectives of measurement accuracy and service life, it is generally believed that in situations of intermittent use (operating for less than 8 hours per day), the sensor aperture should be selected at 1.3 times the actual high flow rate during use. For continuous use (actual daily operation for more than 8 hours), the sensor aperture should be selected at 1.4 times the actual high flow rate during use. As for use under harsh working conditions (such as easily vaporized liquids, liquids containing small particles, etc.), the maximum flow rate during use should be 40% of the allowable maximum flow rate for that caliber. If the diameter of the sensor is not consistent with the diameter of the process pipeline, the pipeline should be modified with a reducing pipe and an equal diameter straight pipe. In general, the error near the lower limit of the sensor flow range is slightly larger. Usually, 0.8 times the actual * small flow rate is selected as the lower limit of the sensor flow range, and a certain margin is ensured.

3. Bearing selection: In order to improve the measurement accuracy of the transmitter, we strive to minimize the friction torque between the shaft and the bearing. General rolling bearings are used for measuring fluids with good lubricity (such as gasoline, kerosene, etc.); Sliding bearings with self-lubricating properties (such as plastic, graphite carbon bearings, etc.) are used in non lubricating liquid measurements; Superhard alloy bearings (such as tungsten carbide bearings) are used for easily vaporized fluids, fluids mixed with small particles, corrosive fluid measurements, and continuous use of transmitters.

2、 Precautions for using turbine flowmeter

1. For flow sensors without bypass pipelines installed, the upstream valve of the flow sensor should be opened at a medium opening first, and then the downstream valve should be slowly opened. Run at a lower flow rate for a period of time (such as 10 minutes), then fully open the upstream valve, and then increase the downstream valve opening to adjust to the required normal flow rate. **Chapter Basic Knowledge

2. For flow sensors equipped with bypass pipelines, first fully open the bypass pipeline valve, open the upstream valve of the flow sensor at a moderate opening, then slowly open the downstream valve, reduce the opening of the bypass valve, and allow the instrument to operate at a lower flow rate for a period of time. Then fully open the upstream valve, fully close the bypass valve (it must be ensured that the bypass valve has no leakage), and then adjust the opening of the downstream valve to the required flow.

3. For low and high temperature fluids, the water in the pipeline should be drained before circulation. When flowing, run at a very low flow rate for 15 minutes and gradually increase to normal flow rate. When stopping the flow, it should also be done slowly to gradually approach the pipeline temperature and ambient temperature.

4. The opening and closing of valves should be as smooth as possible. If automatic control valves are used for opening and closing, it is recommended to use a "two-stage opening, two-stage closing" method to prevent sudden fluid impact on the impeller or even water hammer damage to the impeller.

5. When the pipeline pressure is not high, the downstream pressure of the flow sensor should be checked. Generally, during the initial operation, observe whether the downstream pressure of the sensor is greater than p in equation (1-46) at high flow rates.. Otherwise, measures should be taken to prevent the formation of air pockets.

6. Properly handle the instrument coefficient of the flow sensor, and the instrument coefficient K of the turbine flowmeter should be filled in by the manufacturer on the calibration form provided to the user to prevent loss. When using, carefully check the internal coefficient switch and multiplier switch of the supporting display instrument, and their positions should be consistent with the corresponding sensor coefficients. After long-term use, the coefficient K of the turbine flow sensor may change due to bearing wear and other reasons, and should be regularly verified on-site or offline. If the measurement error exceeds the range, the backup sensor should be replaced in a timely manner, and the display instrument should be reset according to the instrument coefficient of the new sensor in a timely manner.

7. The process flow that requires regular cleaning of pipelines (such as replacing oil products or stopping production of finished oil pipelines), the flow direction, flow rate, pressure, temperature, etc. of the fluid used for pipeline cleaning should comply with the regulations of the turbine flow sensor.

8. When cleaning pipelines with high-temperature steam, it is important to avoid the flow of high-temperature steam through the sensor to prevent damage.

3、 Maintenance of Turbine Flow Meter Instruments

To ensure the long-term normal operation of the turbine flowmeter, it is necessary to regularly check the operation status of sensors, display instruments or flow computers, as well as auxiliary equipment, and carry out maintenance work. Any abnormalities should be promptly eliminated.

1. Regularly disassemble, clean, inspect, and recalibrate the turbine flowmeter; Sensors equipped with lubricating oil or cleaning fluid should be regularly injected with lubricating oil or cleaning fluid according to the instructions to maintain the good operation of the impeller. If there is any abnormal sound from the impeller, the internal components of the sensor should be removed and inspected in a timely manner. When bearings and shafts are severely worn, they should be replaced and recalibrated.

2. Monitor the working condition of the display instrument (shift to "self calibration" mode), evaluate the reading of the display instrument, and promptly check if there is any suspected abnormality.

3. Keep the filter unobstructed. If the filter is blocked by impurities, it can be judged by the increase in the pressure gauge reading difference at its inlet and outlet, and it should be cleared in a timely manner. Otherwise, severe blockage will reduce the flow rate. When the gas sensor that escapes from the liquid in the regular discharge muffler is temporarily removed from the pipeline and not in use, it should be cleaned with light oil and covered with protection at both ends to prevent rust or impurities from entering the instrument.