Selecting Metering Pump Head & Diaphragm Materials by Chemical: 316L, PVC, PP, PVDF, PTFE

In a metering pump, only certain components come into direct contact with the fluid — collectively called the “wetted parts”: the pump head body, the diaphragm or piston, ball valves and valve seats, and gaskets/seals. The drive section (motor, solenoid assembly, cam, gearbox) is isolated and does not contact the chemical. Therefore, when selecting a pump, the first consideration is not flow rate or pressure, but whether the wetted-part materials are compatible with the chemical.

Incorrect material selection leads to three common consequences: corrosion or swelling of the pump head body, degradation and tearing of the metering diaphragm, and leakage at valves or seals. When the diaphragm undergoes micro-corrosion, dosing accuracy begins to drift even though the pump continues running — this is a difficult defect to detect and results in excessive chemical consumption. Material compatibility must therefore be verified before finalizing the pump model.

Each material has its own suitable chemical range. The table below summarizes characteristics and application guidance based on the Doseuro pump head material range:

Note: material compatibility depends simultaneously on chemical type, concentration, and operating temperature. A material compatible with an acid at low concentration and ambient temperature may no longer be safe at high concentration or elevated temperature. The table above serves as a quick reference; the final decision requires cross-checking a dedicated chemical compatibility chart under actual operating conditions.

A common mistake is focusing only on the pump head body material while neglecting the diaphragm. In practice, these two components may be made of different materials and must both be compatible with the fluid. For example: a PVDF pump head body that handles strong acids is paired with a PTFE-coated diaphragm to ensure a chemically inert contact surface. On the Doseuro SDP type S solenoid series, solid PTFE diaphragms are used to handle many corrosive fluids at low flow rates.

Material selection also differs depending on the drive mechanism. Motor-driven mechanical diaphragm pumps and hydraulic diaphragm pumps use flexible diaphragms (typically with a PTFE contact layer); piston pumps use a directly contacting piston, so for high-concentration chemicals at high pressure, inox 316L is preferred for both the piston and pump chamber. When complete leak prevention is required for hazardous fluids, the hydraulic diaphragm type (oil-actuated diaphragm) is a safe option because the diaphragm does not bear direct mechanical pressure.

The table below suggests material selection guidance for common industrial chemical groups, along with suitable Doseuro pump series by drive mechanism:

For water treatment, most common chemicals are well compatible with PVC/PP plastic bodies and PTFE diaphragms at ambient temperature. When dealing with strong acids or oxidizing fluids, PVDF is a safe choice for the pump head body. For high-concentration chemicals combined with high pressure — as found in certain chemical processing or oil & gas applications — inox 316L on piston pump series meets both corrosion resistance and pressure handling requirements.

Correct materials still require correct operating conditions. High fluid temperature narrows the compatibility window for plastics (PVC is more temperature-sensitive than PP and PVDF). Increased concentration also changes how the chemical interacts with the material, so compatibility data must be taken at the actual operating concentration rather than the pure form. Additionally, crystalline deposits or off-gassing (e.g., NaOCl) can cause air-locking of ball valves — pump head and valve design must also be considered, not just material selection.

For maintenance, diaphragms and valve assemblies are wear parts that degrade over time; scheduled inspection intervals allow early detection of corrosion or deterioration before dosing accuracy drifts. For stable metering, pairing a pH/ORP or flow sensor with a 4-20mA control signal is recommended — many Doseuro series support manual or 4-20mA control to automate chemical dosing.