Common Sewage Flow Meter Selection

A sewage flow meter is an instrument used to measure the volumetric flow rate of various types of wastewater within pipes and open channels. It consists of a water level/velocity sensor (probe), a data acquisition unit (logger), and a communication cable.

Sewage flow meters are widely suitable for measuring the volumetric flow of liquids across various sectors, including municipal water supply, steel, petroleum, chemical, power generation, general industry, and water resources management. They are particularly well-suited for flow measurement in channels and small rivers, as well as for sewage metering in environmental protection applications.

Types of sewage flow meter

There are various types of sewage flow meter available, each with its own working principle and applications. Some common types include:

Magnetic Flow Meter

Advantages: No moving parts, resistant to clogging, low maintenance; high measurement accuracy, wide turndown ratio; minimal pressure loss, energy-efficient; suitable for corrosive media, withstands corrosive chemicals in sewage; capable of measuring both forward and reverse flow.

Disadvantages: Requires full pipe flow, pipeline must be completely filled with liquid; requires conductive liquid, unsuitable for non-conductive liquids like pure water or oils, though this is rarely an issue in wastewater treatment; Relatively high initial investment; Susceptible to external electromagnetic interference, requiring proper grounding and wiring.

Applications: The most commonly used and widely applied flowmeter type in wastewater treatment plants. Suitable for full-pipe pressure pipelines such as: - After the influent pump station; - Between process units (e.g., aeration tank inflow/outflow, secondary clarifier inflow/outflow, return sludge, excess sludge); Outfall points.

Ultrasonic Flow Meter

Advantages: Utilizes a non-contact measurement method. Suitable for large-diameter pipelines and wastewater containing impurities. Compared to electromagnetic flow meters, ultrasonic flow meters offer distinct advantages for installation on large pipe diameters (especially those exceeding 1 m), with relatively low installation complexity, cost, and maintenance requirements.

Disadvantages: Requires fluids to be essentially free of bubbles and solid particles, demanding high cleanliness standards.

Suitable Applications: Cleaner water sources such as treated water, reclaimed water, and effluent from aeration tanks.

Vortex Flow Meter

Measures fluid velocity by detecting the frequency of Karman vortices generated when fluid flows past an obstacle. Suitable for measuring low-to-medium viscosity liquids free of impurities, commonly used in monitoring lightly contaminated industrial wastewater.

Disadvantages: Sensitive to vibration and impurities, prone to interference; unsuitable for high-viscosity wastewater or sewage containing large amounts of solid particles.

Suitable Applications: Low-viscosity, relatively clean wastewater (e.g., industrial effluent).

Mass Flow Meter

Advantages: Directly measures mass flow with exceptional accuracy; unaffected by fluid properties (density, viscosity).

Disadvantages: High cost and demanding installation requirements; unsuitable for large pipe diameters or wastewater with high suspended solids.

Applications: High-precision wastewater measurement (e.g., chemical and pharmaceutical industries).

Rotary Flow Meter

Advantages: Simple structure, intuitive display.

Disadvantages: Prone to clogging, requires regular cleaning; unsuitable for wastewater containing solid particles or high viscosity.

Suitable Scenarios: Low-flow, low-viscosity wastewater (e.g., laboratory or small-scale treatment).

Turbine Flow Meter

Measures flow by the rotational speed of a turbine driven by fluid flow. Features simple structure, fast response, and high accuracy. Suitable for clean or slightly contaminated wastewater measurement, commonly used for industrial cooling water and lightly treated effluent metering.

Disadvantages: Turbine prone to wear; unsuitable for wastewater containing solid particles.

Suitable Scenarios: Relatively clean, low-corrosive wastewater.

Open Channel Flow Meter

Primarily used for measuring wastewater flow in open channels, typically operating in conjunction with level gauges and velocity meters. Widely applied in urban stormwater drainage, agricultural irrigation drainage, and similar scenarios.

How to Select a Sewage Flow Meter

1. Understand the Wastewater Profile

Before selecting a sewage flow meter, it is essential to determine the type of industrial wastewater requiring measurement. Common sources include power plants, steel mills, chemical plants, paper mills, and municipal sewage. Different types of wastewater are suited to different flow meters. For instance, a flow meter used in a paper mill is specifically designed to handle its unique effluent.

It is equally critical to identify the wastewater's composition to correctly select the flow meter's liner and electrode materials. Key factors include the corrosiveness of the effluent and the concentration of suspended solids and debris. If the wastewater composition is not fully known, analyzing the material of the existing sewage pipelines can provide insight into the fluid's corrosiveness. This information is then used to select a flow meter with appropriate corrosion resistance.

2. Thoroughly Assess Installation Conditions

The on-site environment where the flow meter is to be installed directly impacts the selection of a sewage flow meter. It is crucial to fully evaluate factors such as upstream straight-run pipe requirements and potential ambient interference. Different sewage flow meters have specific environmental prerequisites. For example, electromagnetic flow meters require a certain length of straight pipe upstream for accurate measurement, an environment free from strong electromagnetic interference, and must operate within specified temperature and humidity ranges.

3. Understand Flow Meter Performance

When selecting a flow meter, it is essential to be familiar with the performance characteristics of various sewage flow meter types. Key factors to consider include accuracy, repeatability, linearity, turndown ratio, and output signal. Furthermore, understanding the diameter of the sewage pipeline is critical, as different flow meters have specific requirements. For instance, each bore size of an electromagnetic flow meter has a minimum flow rate requirement; if the actual flow falls below this threshold, the measurement accuracy will deviate significantly from the true value.

In summary, there is a wide variety of flow meters designed for wastewater measurement, with each type being suited for different applications. When selecting a sewage flow meter, factors such as measurement range, accuracy, and reliability must be considered to ensure the choice aligns with the specific practical requirements.