Principle analysis of various types of flowmeters
(1) Principles of mechanics: Instruments belonging to such principles have differential pressure and rotor type using Bernoulli's theorem; impulse type and movable tube type using momentum theorem; direct mass type using Newton's second law; The target type of the momentum principle; the turbine type using the angular momentum theorem; the vortex type using the principle of fluid oscillation, the vortex type; the pitot tube type using the total static pressure difference; the volumetric type, the enthalpy, the trough type, and the like.
(2) Electrical principle: The instruments used for such principles are electromagnetic, differential capacitive, inductive, strain resistant, etc.
(3) Acoustic principle: Ultrasonic type, acoustic type (shock wave type), etc. are used for flow measurement using the acoustic principle.
(4) Thermal principle: The heat, direct thermal, indirect calorimetry, etc., which measure the flow using the thermal principle.
(5) Optical principle: laser type, photoelectric type, etc. are instruments belonging to such principles.
(6) Originally based on physical principles: nuclear magnetic resonance, nuclear radiation, etc. are instruments of this type.
(7) Other principles: Marking principle (trace principle, NMR principle), related principles, etc.
Fourth, the liquid turbine flowmeter put into operation the opening and closing sequence
1. The sequence of opening and closing of the operation
For flow sensors without a bypass line, first open the flow sensor upstream valve at a medium opening and then slowly open the downstream valve. Run at a small flow rate for a period of time (eg 10 minutes), then fully open the upstream valve, then open the large downstream valve opening to adjust to the required normal flow.
The flow sensor equipped with the bypass pipe first opens the bypass pipe valve to open the upstream valve at a medium opening degree, slowly opens the downstream valve, and closes the opening of the small bypass valve to make the instrument run for a period of time with a small flow rate. Then fully open the upstream valve, fully close the bypass valve (to ensure no leakage), and finally adjust the downstream valve opening to the required flow.
2. Activation of low temperature and high temperature fluids
The low-temperature fluid pipeline should drain the water in the pipeline before the flow, and then run for 15 minutes at a small flow rate, and then gradually increase to the normal flow. Slow down when stopping, so that the pipe temperature and ambient temperature are gradually approaching. High temperature fluid operation is similar to this.
Second, the compressed air vortex flowmeter installation steps
1. The special flanges to be equipped are welded to the upstream and downstream straight pipe sections respectively, so that the inner diameters of the special flange and the straight pipe section are strictly vertical and concentric.
2. Install the sensor clip on the upper and lower straight pipe sections welded with special flanges and fasten them with bolts. The upstream and downstream straight sections should be kept concentric with the sensor.
3. It should be noted that the flow direction of the sensor should be consistent with the flow direction of the fluid in the pipeline.
Third, special attention should be paid when installing compressed air vortex flowmeter
1. When welding special flanges and straight pipe sections, the sensor should be removed and the sensor welding flange must not be carried.
2. Before the sensor is installed, the sealing ring must be placed in the groove of the flange.
3. The pressure point and temperature measurement point should be at the 3DN~5DN and 6N~8DN downstream of the sensor.
4. When the high temperature pipeline is insulated, do not wrap the sensor to avoid damage.
5. The cable connecting the vortex flowmeter should be as far away as possible from the interference of strong electromagnetic fields. It is absolutely not allowed to lay with high voltage cables. The shielded cable should be as short as possible, the maximum length should not exceed 500 meters, and should not be coiled to reduce the distributed inductance.