Classic Venturi Flow Meter/Insertion-type Venturi Flow Meter – Dayue Instrumentation

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Classification of venturi flow meters: Venturi flow meters are classified into pipe-type venturi flow meters and insert-type venturi flow meters based on their installation methods. 1. Pipe-type venturi flow meters can be further divided into conventional venturi flow meters (for ordinary pipes) and built-in venturi flow meters. They are primarily used for measuring the flow rate of gases with large diameters, low flow velocities, and high flow rates in industrial enterprises; they feature a sophisticated design and are calibrated using actual flow conditions in large-scale wind tunnel laboratories. It can be widely used for the control and measurement of large-diameter fluids in industries such as petroleum, chemicals, metallurgy, and power generation. 2. The insert-type venturi flow meter is used in applications where the pipe diameter is too large, the straight pipe section available for the device is short, or the location of the device is constrained, and where high accuracy in flow measurement is not required. It features easy installation without the need to cut the pipe, as well as low cost. Currently, it is often used as a replacement for built-in venturis and wing anemometers for measuring air flow rates. Based on the different manufacturing methods, they are classified into classic Venturi flowmeters with a roughly cast shortened section, Venturi flowmeters with a mechanically processed shortened section, and Venturi flowmeters with a roughly welded steel plate shortened section. The classic venturi flow meter is a throttling type flow sensor developed based on the venturi effect; it is a standard throttling device. Based on their structure, venturi tubes are divided into standard venturi tubes and universal venturi tubes. Standard (classic) venturi tubes are classified into standard venturis with a rough-cast contraction section, standard venturis with a mechanically machined contraction section, and standard venturis with a roughly welded plate contraction section, depending on their manufacturing method. The General Venturi series of flow sensors not only inherit the advantages of standard venturi tubes, such as high accuracy, good repeatability, low pressure loss, and short required straight pipe length, but also feature a compact design and resistance to clogging. It can be used to measure complex flow problems such as two-way flow, mixed-phase flow, low flow rates, large pipe diameters, and irregular-shaped pipes. In a standard throttling device, it requires short straight pipes upstream and downstream, low pressure loss, stable performance, and easy maintenance. Due to its accurate calculations and low energy consumption, it has been widely used in the petroleum, chemical, power, and metallurgy industries. Performance characteristics of the venturi flow meter: High precision, equipped with a high-accuracy differential pressure transmitter to enable the measurement of the total flow rate. It has good reliability; the total flow rate index remains at a constant level, ensuring a long service life for measurement and calibration. The accuracy class (division value ratio) is wide; no further adjustment through the software is required, as the ratio can exceed around 12:1. It has strong adaptability to different media, and can accurately measure the fluid dynamics of high-pressure and low-pressure conditions, as well as those involving gases with high humidity levels and various types of contaminants. Setting a low requirement for the installed transition section can reasonably prevent or reduce the additional measurement uncertainty of the detection system. It causes minimal work-related stress and saves resources. Key technical parameters of the venturi flow meter:
1. Nominal diameter: 50 mm ≤ DN ≤ 3000 mm; Rough-cast contraction section: 100 mm ≤ DN ≤ 1600 mm; Machined contraction section: 20 mm ≤ DN ≤ 250 mm; Rough-welded steel plate contraction section: 100 mm ≤ DN ≤ 3000 mm.
2. Throat area ratio β: 0.3 ≤ β ≤ 0.75; Rough-cast contraction section: 0.3 ≤ β ≤ 0.75; Machined contraction section: 0.4 ≤ β ≤ 0.75; Rough-welded steel plate contraction section: 0.4 ≤ β ≤ 0.7.
3. Reynolds number range: 2×105 ≤ ReD ≤ 2×106; Rough-cast contraction section: 2×105 ≤ ReD ≤ 2×106; Machined contraction section: 2×105 ≤ ReD ≤ 106; Rough-welded steel plate contraction section: 2×105 ≤ ReD ≤ 2×106.
4. Accuracy class: Class 0.5, Class 1, Class 1.5, Class 2.
5. Operating pressure: Nominal pressure: PN ≤ 42 MPa.
6. Medium temperature: -50°C ≤ t ≤ 500°C.
7. Reference standards: GB/T 2624-2006, JJG 640-94, and ASME PTC 19.5-2004.
8. Connection methods: Flange connection, welding, threading.

Installation requirements for the venturi flow meter:
1. First, cut two straight pipe sections with the same diameter as those of the pressure tapping elbow, with a length of more than one time the diameter. 2. On a platform (or flat surface) with favorable conditions, weld the two cut straight pipe sections to the pressure-taking elbow at a 90° perpendicular angle, ensuring good welding quality. 3. Install the pre-fabricated pipes and weld them to the process pipes. 4. The venturi tube sensor should be welded to the process pipeline, ensuring that it operates in a horizontal position as much as possible. When horizontal installation conditions are not available on site, it can be installed in a vertical orientation. The venturi tube flow sensor is connected to the process pipeline via flanges, and can be aligned horizontally with the process pipeline in accordance with the direction indicated on the sensor. When installing a venturi tube, the length of the straight section at the front end should be more than 5 times the diameter, while the length of the straight section at the rear end should be more than 2 times the diameter.