How does a waste water flow meter work?

Used to measure the volumetric or mass flow of waste water, sewage or trade effluent, a waste water flow meter works by measuring the amount of waste water that flows through, under or around flow meter sensors.

There are three specific ways to measure open channel water using a waste water flow meter, each of which works in a different way:

Insertion waste water flow meter

Usually referred to as an ‘area velocity flow meter’, our MSFM is a perfect example of an insertion waste water flow meter. Installed at the bottom of the pipe in the water, an insertion waste water flow meter will measure depth and velocity and calculate flow. It is one of the most effective methods of waste water flow monitoring.

Non-contact water flow meter

Works similarly to an insertion flow meter but measures level and surface velocity. It is installed above the flow of water rather than in the actual pipe. A non-contact flow meter is ideal for circumstances where equipment cannot come into contact with the flow, such as flammable liquid, where access is limited, or where debris in the water may disrupt the measurement. Non contact measurement isn’t as accurate as that from an insertion waste water flow meter since surface friction will always affect data.

Primary device

Weirs and flumes are both examples of primary devices that can be used to monitor the level of flow. Our MSFM Lite level meter is used extensively in such applications. A primary device offers a level-only system and often requires a degree of civils work before it can be realised. When a primary device is installed, it regulates the flow and causes the levels to rise. The change in level is used to measure flow. The formula relationship between level and flow is used when a standard primary device is implemented. Primary devices are not suitable for network monitoring but are used predominantly for measuring trade effluent.

Depending on what is required to be measured by the waste water flow meter i.e. volume or mass, the metrics can be expressed as follows:

Measuring volume: the volume of water (Q) is equal to the wetted cross-sectional area of the pipe (A) times the average velocity of the water (v)

Q = A x v

Measuring mass: the mass flow of water passing through a flow meter (W) is equal to the fluid density (r) times the volume of water (Q)

W = r x Q