Cooling tower bleed control systems, incorporating the selection of appropriate valves, are critical for managing dissolved solids and maintaining system efficiency in industrial processes, says boiler manufacturer and water treatment equipment supplier Allmech.

The company explains that cooling towers rely on evaporation to remove heat, but this process concentrates dissolved solids in the system. If left unmanaged, this can lead to scaling, corrosion and fouling, reducing efficiency and increasing maintenance costs.

Allmech water treatment consultant Anelia Hough explains that without proper bleed control, dissolved solids begin to affect system performance.

“Bleed, or blowdown, involves removing a portion of high total dissolved solids water from the system and replacing it with fresh make-up water. This helps keep dissolved solids within acceptable limits and supports chemical treatment programmes,” she explains.

Hough outlines two main approaches to managing bleed. One is a time-based system which uses a timer to open a valve at set intervals. This is a simple and reliable method that does not rely on probes or controllers.

The other is a conductivity-controlled system that measures water conductivity as an indicator of dissolved solids. When levels exceed a defined threshold, the system automatically opens the bleed valve.

Each system has trade-offs. Time-based systems are easier to install and operate, with lower upfront costs and fewer components. “However, they can be less efficient and may result in unnecessary water loss,” she says.

Conductivity-controlled systems require higher initial investment and ongoing probe maintenance, including cleaning and calibration. In return, they provide tighter control, which can reduce water and chemical use over time, if maintained correctly.

Hough says the choice between systems depends on the operating environment. Time-based systems are suited to smaller installations or where water quality is stable and predictable. “Conductivity-controlled systems are more suitable for larger or more complex operations, particularly where water sources vary,” she says.

She adds that valve performance plays a key role in time-based systems. Most use solenoid valves, which provide fast and precise actuation but can be sensitive to fouling and wear, especially in harsh conditions. These valves often require regular maintenance and seal replacement.

Hough notes that ceramic ball valves can be used in certain time-based applications. These are designed for durability, with wear- resistant components that perform reliably in abrasive or poor-quality water. “Although actuation may be slower, they offer longer service life, reduced risk of water hammer and improved resilience,” she notes.

Hough explains that over-bleeding wastes water and chemicals, while under-bleeding allows dissolved solids to accumulate. She stresses that even simple systems require regular monitoring, including routine testing and periodic adjustments.

Hough concludes that there is no single solution, advising consultation with an experienced service provider to assess requirements and recommend a suitable approach.