When treating water or wastewater often two types of chemical metering/dosing pumps are considered. The chemical feed unit must be able to measure the precise amounts of chemical to meet, but not exceed, chemical demand.
This poses the question of which is most effective and reliable, a diaphragm pump or a peristaltic pump. Both are positive displacement pumps but work in very different ways.
The diaphragm pump can appear more cost effective than the peristaltic pump but has its challenges. The diaphragm has a pumping cycle that consists of a suction and discharge phase. This intermittent pumping of chemicals, specifically during the suction phase of the cycle, can cause gas build up. This buildup of gases can cause vapor lock and the pump may lose prime.
Diaphragm pumps have check valves in the suction and discharge ends of the pump head. If either set of check valves becomes fouled, the pump will not meter chemical accurately, if at all. Loss of prime may occur. Diaphragm pumps can also create shear stress on fluids, particularly if the pump employs a high velocity stroke action.
Fluids containing particulates, and gas forming chemicals can foul heads and valves.
Routine maintenance procedures must be performed, in particular the cleaning of check valves and inspection of diaphragms.