Question: Our floating pumps occasionally suck up trash and vegetation from the lake's bottom. How can we protect our water flowmeter from the debris that gets through pump's strainer?

Answer: Intake strainers on large-volume freshwater pumps provide protection for the pump vanes without minimizing water flow. While these prevent large pieces of debris from entering the pipe, they are not designed to completely clean the water. Particles large enough to damage turbine flowmeters and affect concrete quality often pass through. Since blade and bearing designs vary widely in water-meter design, it is important for producers to follow manufacturer installation recommendations. The mesh size of the strainer's screen is based on the size of the flowmeter. The table below lists recommended strainer mesh numbers. Bronze-bodied "Y" strainers are the best choices. You could use a less-expensive cast iron- bodied strainer, but over time it can rust and corrode. The strainer should be the same diameter as the meter's intake pipe to avoid flow restriction.When installed too close to the meter's measuring turbine, strainers compromise the accuracy of flow readings. This is caused by cavitation and turbulence created as water passes through the strainer's screen openings. Manufacturers recommend a minimum distance between strainer and meter inlet of 10 times the pipe's inside diameter. For example, a strainer on a 3-inch pipe should be installed at least 30 inches away from the meter.Also, when installing the strainer, make sure no electrical equipment is in the strainer-drain plug's outfall path.Water-meter manufacturers suggest that all concrete plants, even those supplied with municipal water, benefit from properly placed strainers. Producers have reported water-meter damage by debris from pipeline repairs performed miles away from the plant, or scaling from the linings of older city pipes.

Source: Flow Measurement Engineering Handbook, R.W. Miller, McGraw-Hill Publishing Co.
Typical Mesh Numbers for Upstream Strainers
Flowmeter Size (inches)
Mesh No.
1/2, 3/4
100
1, 2, 3
80
4, 6
60
8, 10, 12
40