Switch Offers Improved Chemical Additive Flow Monitoring

Whatever the industrial water treatment process, a fundamental step in water treatment frequently includes the use of chemical additives ...

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By Malcolm McQueen

Whatever the industrial water treatment process, a fundamental step in water treatment frequently includes the

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The Model FLT93L Inline Flow Switch from Fluid Components International.
use of chemical additives such as alum, polymer, caustic soda, ferric chloride and others. Their dispensing is critical to the success of wastewater treatment.

To dispense and meter chemical additives, positive displacement pumps are commonly employed at multiple points in wastewater treatment processes. The quantities of chemical additives are relatively small in typical industrial water treatment processes with flow rates of 1 to 2 gallons per hour. Plant operators must continually monitor pump flow rates and the additives to ensure a safe operating environment.

It is a common industry practice to assume chemical additives are flowing as long as the displacement pump actuators are moving. However, pump actuator movement does not guarantee chemical additive flow. For example, chemical reservoirs can run dry, blocking valves are accidentally closed, lines leak and injectors clog — all while the pump’s actuator continues its cyclic motion.

Monitoring the flow of chemical additives is a more reliable way to ensure chemical flow and to avoid a variety of problems. Unfortunately, flow monitors typically are not sensitive enough to detect extremely low flow rates nor robust enough to withstand the harsh and/or corrosive chemicals required in wastewater treatment. The consequence of not monitoring chemical additive flow can range from damage to equipment to contamination of the end-product to expensive citations for water pollution.

A simple solution has been created to solve the problem of monitoring chemical additives in wastewater. An inline (spool-piece) thermal dispersion flow switch with a special flow amplifying orifice provides a sensitive and reliable chemical additive monitoring instrument.

While there are many different types of flow switches available from multiple manufacturers, the Model FLT93L Inline Flow Switch from Fluid Components International (FCI) is well suited for chemical additive monitoring. Designed for rugged industrial processes and manufacturing environments, they have proven themselves responsive and dependable in both industrial and municipal wastewater treatment applications.

The FLT93L thermal flow switch operates over a range from 0.3 to 420 gph, accommodating the low flow requirements necessary for monitoring chemical additives. It features two 6A relays, which the plant operator can program as alarm trip points to indicate early warning of no-flow conditions.

Thermal flow switches are a popular choice for process and industrial plant wastewater treatment applications. They offer accuracy and, because there are no moving parts to clog or foul, reliability. The highest quality thermal flow switches always include temperature-compensated circuitry, a mean time between failure (MTBF) rating of 190 years and carry a SIL2 compliance rating. Their wetted parts can be specified with a variety of materials compatible with the chemicals being measured and for operation in harsh plant environments.


About the Author: Malcolm (Mac) McQueen has been designing and applying thermal flow switch solutions for industrial customers for more than four decades. An original founder of Fluid Components International, he holds numerous design patents for innovative flow and level measurement products applied in industrial, aerospace and nuclear power plant applications.

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