What is a chemical dosing device for cooling towers? Methods for injecting water treatment chemicals [Basic Knowledge]

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last updated：Nov 15, 2026

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A dosing device that maintains the concentration of cooling water chemicals. It explains the differences between supply water volume proportional control and timer control, interlocking with the blow-off device, and the concept of injection volume.

■What does the chemical injection system do? The chemical injection system for cooling towers injects water treatment chemicals into the cooling water to maintain the concentration of chemicals in the cooling water. Generally, it consists of a tank for holding the chemicals and a chemical injection pump for delivering the chemicals, and it is used in combination with an automatic blow-off device. Scale inhibitors, corrosion inhibitors, and slime inhibitors each need to maintain appropriate concentrations. ■Why is it necessary to keep injecting? In open cooling towers, cooling water evaporates and decreases, so to prevent it from becoming too concentrated, water is discharged through blow-off, and this is supplemented with make-up water. Since chemicals are also discharged along with the water during blow-off, if injection is not continued, the concentration of the chemicals will dilute. Multifunctional chemicals exert their effects when continuously injected by the chemical injection system. ■Initially, inject all at once After chemically cleaning the cooling tower, an initial dose of chemicals is added to the cooling tower's basin, and the chemical injection pump is activated to ensure continuous injection at the start of operation. This is to secure the necessary concentration from the moment operation begins. The concentration guideline is 100 to 500 mg/L, depending on the type of chemical. Please feel free to consult us first.

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■ How is the injection amount determined? The injection amount of the chemical is adjusted using either a proportional method based on the makeup water amount or a timer control method during cooling tower operation. ■ What is the proportional method based on makeup water amount? This method measures the amount of makeup water with a flow meter and operates the chemical injection pump in proportion to that amount. It can be connected to a flow meter that outputs a pulse signal, which is used to operate the pump. As the makeup water increases, the injection amount also increases, making it easier to maintain a constant concentration in the cooling water. ■ What is the timer control method? This method operates the chemical injection pump only for a set interval and duration during the operation of the cooling tower. For example, it may be set to operate for one minute every hour. While the mechanism is simple, the injection amount does not automatically change with variations in the makeup water amount. Adjustments to the settings may be necessary in summer when evaporation is high and in winter when it is low. ■ Linking with the blow-off device There is also a method to operate the chemical injection pump in conjunction with an automatic blow-off device. The automatic blow-off device monitors the electrical conductivity of the cooling water and replaces the water when concentration increases. Since the chemical is also expelled when water is discarded, the idea is to supplement the chemical in accordance with that action.

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■How much should be added to the make-up water?! Assuming that the chemicals are not consumed, the chemicals that exit are those contained in the blowdown water. If the concentration factor (approximately make-up water volume ÷ blowdown water volume) is 4, then you should add one-fourth of the desired concentration to the make-up water to balance the inflow and outflow. If the desired maintenance concentration is 100 mg/L, then it would be 25 g per cubic meter of make-up water. If the make-up water is 20 cubic meters per day, that amounts to 500 g per day, or 15 kg over 30 days, which serves as a guideline for tank size. The actual injection amount will be determined based on individual water treatment plans. ■Check the concentration during operation During the operation period, analyze the chemical concentration and adjust the maintenance concentration. This is because both the initial concentration and the maintenance concentration vary depending on the type of chemical. It is important to actually measure and confirm whether the concentration is as calculated. ■What to do with small cooling towers? For small cooling towers, simple chemical injection devices using dry batteries can also be utilized. Our company provides advice on selecting chemical injection devices suitable for the scale of the cooling tower and the amount of water treatment chemicals to be injected. Please feel free to consult with us first.