WOH Diaphragm Metering Pump Guide

A diaphragm metering pump is a positive-displacement device where an electric motor drives an eccentric cam or solenoid to move a flexible diaphragm back and forth. Each back-stroke draws chemical into the pump head through a suction check valve; each forward stroke pushes it out through a discharge check valve to the injection point. The diaphragm—usually PTFE or PTFE-coated—physically separates the chemical from the drive mechanism, making these pumps the standard for chlorine dosing in small drinking water systems.

Key components that require attention are the suction and discharge check valves (worn or fouled valves cause low or erratic output), the diaphragm (cracks or fatigue cause loss of output and leakage), the pump head (must be compatible with the chemical being dosed), and the injection quill and check valve at the point of entry (a broken quill or failed valve results in zero delivery). The foot valve and suction strainer at the day tank bottom must be kept clean to maintain prime and prevent particulates from entering the pump head.

Unlike centrifugal pumps, a diaphragm metering pump delivers approximately the same volume per stroke regardless of system pressure—within its rated pressure range. However, if discharge pressure exceeds the pump's maximum rating, output will drop and the pump may stall; always verify the pump's pressure rating exceeds the static pressure at the injection point.

During installation, mount the pump at or below the day tank level to prevent air-lock, use only manufacturer-specified tubing material, keep suction lines short and direct, verify all wetted parts are compatible with the chemical and its concentration, and prime the pump before first use. Never run the pump dry, as this damages the diaphragm and check valves.