The Venturi flowmeter is used to measure the flow rate of single-phase stable fluids in closed pipelines, and is commonly used to measure the flow rate of fluids such as air, natural gas, coal gas, water, etc.

The basic measurement principle of the new generation differential pressure flow measurement instrument is based on the law of conservation of energy - Bernoulli equation and flow continuity equation as the basis for flow measurement method. The inner tube is composed of a circular measuring tube and a special core body placed inside the measuring tube and coaxial with the measuring tube. The radial outer surface of the special core has a geometric profile similar to the inner surface of the classical Venturi tube, and forms a reduced diameter annular flow gap with the inner surface of the measuring tube. The throttling process of fluid flowing through an inner Venturi tube is basically similar to the throttling process of fluid flowing through a classical Venturi tube and an annular orifice plate. The structural characteristics of the inner tube make it free from sharp edge abrasion and fouling problems similar to orifice plate throttling components during use, and can effectively adjust the flow gradient and possible non axisymmetric velocity distribution inside the tube before throttling (flow regulation), thereby achieving high-precision and high stability flow measurement.

classification

1、Classic Venturi tubeApplied to flow measurement of various media, it has the characteristics of small permanent pressure loss, short required front and rear straight pipe sections, and long service life.

2Sleeve type Venturi tube: mainly used for flow measurement and control of various large-diameter and high-pressure or hazardous media in the petrochemical industry.

3、.Venturi nozzle: Suitable for measuring various media, it has the characteristics of low permanent pressure loss, short required front and rear straight pipe sections, and long service life. The installation length of the body is shorter than that of the classic Venturi tube.

1. Nominal diameter:50mm≤DN≤1200mm ,exceed1200mmCalibration is required
·Rough casting shrinkage section:100mm≤DN≤800mm
·Mechanical processing shrinkage section:50mm≤DN≤250mm
·Shrinkage section of rough welded iron plate:200mm≤DN≤1200mm

2. Throttle aperture ratio β:0.3≤β≤0.75
·Rough casting shrinkage section:0.3≤β≤0.75
·Mechanical processing shrinkage section:0.4≤β≤0.75
·Shrinkage section of rough welded iron plate:0.4≤β≤0.7

3. Reynolds number range: 2×105≤ReD≤2×106
·Rough casting shrinkage section:2×105≤ReD≤2×106
·Mechanical processing shrinkage section:2×105≤ReD≤106
·Shrinkage section of rough welded iron plate:2×105≤ReD≤2×106

4. Accuracy level:1level

advantage:If we could follow it completelyASMEStandard precision manufacturing, measurement accuracy can also reach0.5%,However, due to manufacturing technology issues, domestically produced Venturi,Accuracy is difficult to guarantee,The Kaifeng Instrument Factory, which has a strong technical force and a long-standing qualification in China, can only guarantee4%Measurement accuracy, for the working conditions of ultra supercritical power generation, the use of a pressure equalization ring at the throat is a very dangerous link under high temperature and high pressure. Without using a pressure equalization ring, it does not meet the requirementsASNE ISO5167The standard and measurement accuracy cannot be guaranteed, which is a contradiction in high-pressure classical Venturi manufacturing.

Disadvantages:Pipe and inlet/Export the same material,The fluid has severe erosion and wear on the throat, which cannot guarantee long-term measurement accuracy. The length of the structure must be in accordance withISO-5167Regulations on Manufacturing,Otherwise, the required accuracy will not be achieved,due toISO-5167Strict structural regulations for the classic Venturi,Maximize its flow measurement range/The minimum flow ratio is very small,Usually in 3 – 5 between. It is difficult to meet the requirements of flow measurement with large changes in flow rate.

answerventuri meterDuring installation:

1Firstly, cut two straight pipe sections with the same diameter as the pressure elbow, with a length of1More than twice the diameter.

2On platforms with better conditions(Or flat ground)On top, weld the two straight pipe sections that have been cut with the pressure bending pipe, forming90oVertical state and ensure welding quality

3Weld the prefabricated pipeline onto the process pipeline.

4The Venturi tube sensor is welded to the process pipeline to work as horizontally as possible. When horizontal installation conditions are not available on site, installation can be carried out in a vertical spatial state.

The Venturi tube flow sensor is connected to the process pipeline via a flange, and can be aligned with the process pipeline in a horizontal spatial state according to the flow direction indicated by the sensor.

When installing the Venturi tube, the length of the straight pipe section at the front end should be greater than5Double the diameter, the length of the straight pipe section at the rear end should be greater than2Double the diameter.

Pre work inspection

1Check each transmitter(Including differential pressure, pressure, and temperature transmitters)Whether the piping, installation, and wiring are correct.

2Check whether all welding interfaces and threaded joints are tight and leak proof.

3Check whether the wiring of the secondary instrument is correct, whether the wiring between each transmitter is correct, and focus on checking the position of the power connector.

4After the above checks are correct, connect the secondary instrument power supply.