What component should a chemical feed machine have on the feed line to avoid back siphonage when pumping sodium fluoride?

A check valve is essential in a chemical feed machine's feed line to prevent back siphonage, particularly when dispensing substances like sodium fluoride. Back siphonage occurs when there is a negative pressure in the supply line, which can draw contaminants back into the clean water supply. The check valve functions as a one-way device that allows fluid to flow in only one direction. This means that if there is a drop in pressure or a reversal in flow direction, the check valve will close, effectively blocking any potential for backflow from the distribution system back into the source.

Using a check valve is a standard practice in water treatment and chemical feed systems to maintain water quality and prevent cross-contamination, ensuring that harmful chemicals do not enter the drinking water supply. The other components mentioned serve different functions: a flow meter measures the amount of chemical being delivered, a pressure relief valve protects against overpressure situations, and a chemical injector is used to introduce chemicals into the water supply. None of these fulfill the vital role of preventing back siphonage as effectively as a check valve.