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Creation of a constant flow requires a constant driving force and a constant pressure coefficient or loss coefficient. An almost constant driving force can be obtained by using a very large driving head with small variations due to level fluctuations in the stock tanks. A more practical approach is to use a float valve to regulate the chemical level in a small tank. The constant fluid level can then be used to develop a constant flow. Recent advances in small low cost chemical resistant float valves has have made it possible to use float valves even with corrosive chlorine solutions.

Flow control modules will generate a linear response between head loss and chemical flow rate as long as expansion losses are small relative to shear losses and as long as the flow is laminar.
Design of the flow control module consists of choosing a maximum head loss corresponding to the maximum design flow rate, and then determining the diameter and length of the tubing.