The Venturi flowmeter is a differential pressure flow measurement instrument based on fluid dynamics principles. It calculates the flow rate by measuring the pressure difference generated when the fluid flows through the Venturi tube.

• Classic Venturi Tube: Suitable for clean liquids/gases, with low pressure loss and low requirements for straight pipe sections (5D before and 2D after).
• Tubular Venturi Tube: Specifically designed for high-pressure or hazardous media (such as natural gas), featuring a double-layer structure to prevent leakage.
• Venturi Nozzle: With a shorter installation length, it is suitable for space-constrained scenarios.

The advantages of the Venturi flowmeter almost all stem from its streamlined geometric structure:

1. Extremely low permanent pressure loss
   • This is its core advantage. Compared with instruments that cause sudden throttling such as orifice plates and wedge flowmeters, the pressure recovery efficiency of the Venturi tube is very high, typically reaching 85% - 90%. This means that the energy consumption of the pump used to overcome the resistance of the flowmeter is extremely low, resulting in significant energy-saving effects over long-term operation.
2. High accuracy and good repeatability
   • Accuracy can reach ±0.5% to ±1.0%.
   • Due to its streamlined design which causes minimal disturbance to the fluid, the flow coefficient is very stable and has good repeatability.
3. Wear-resistant and dirt-tolerant
   • The smooth profile without sharp edges or stagnation zones makes it very suitable for measuring liquids containing small amounts of solid particles (such as circulating water, raw water), as particles are less likely to wear the throttling element or get stuck.
   • Compared to orifice plates, it is less sensitive to suspended solids upstream.
4. Wide rangeability
   • The rangeability is typically 10:1, which is better than that of orifice plates.
5. Relatively low requirement for upstream straight pipe sections
   • Due to its streamlined design which shapes the fluid, it is less sensitive to the upstream flow conditions than orifice plates. Typically, the upstream straight pipe section requirement is 5-10D.

According to different manufacturing methods, Venturi tubes are mainly classified as follows:

1. Classic Venturi Tube:
   • Cast Contraction Section: The inlet section is cast, and the throat is machined.
   • Machined Contraction Section: Both the inlet section and the throat are precisely machined, offering the highest accuracy but also the highest cost.
   • Rough Welded Iron Plate Contraction Section: Used in large-diameter and low-precision requirements scenarios, such as water conservancy projects.
2. Venturi Nozzle:
   • A standard ISA 1932 nozzle is installed at the inlet of the classic Venturi tube. Its performance lies between that of orifice plates and classic Venturi tubes, and it is shorter in length.

• Industrial fields: Petrochemical (raw material/fuel measurement), power (cooling water monitoring), metallurgy (coke oven gas measurement).
• Environmental protection and water treatment: Wastewater flow monitoring, gas emission control (such as CO₂, NOₓ).
• Special working conditions: Low-temperature media (liquid nitrogen, liquid oxygen), high-pressure steam (temperature resistance up to 530℃, pressure resistance up to 40MPa).

Conclusion: The Venturi flowmeter is the "high-performance sports car" among differential pressure flowmeters. Through its precise streamlined design, it sacrifices a high initial investment to achieve extremely low operating energy consumption and outstanding long-term measurement performance. In scenarios with large flow rates, continuous operation, and high pumping energy consumption, choosing a Venturi flowmeter is often a wise long-term investment.