Metal vs. Plastic Body Diaphragm Pumps: How to Choose the Right One for Each Application

An air-operated double diaphragm pump (AODD) uses compressed air as the driving force to alternately move two diaphragms, requiring no mechanical seals or electric motors in contact with the fluid. As a result, the same pump platform can switch between a metal body and a plastic body while retaining the same core advantages:

• Seal-less — reduces leakage and failure points compared to rotary pumps.
• Self-priming and safe for dry running — suitable for draining tanks and drawing from low positions.
• Low shear — handles shear-sensitive fluids, emulsions, and fluids containing solids.
• Handles viscous, abrasive, and high-solids fluids — optional ball valves or flap valves depending on application.

!The body material determines mechanical durability and installation environment, but the diaphragm and ball valve materials are what come into direct contact with the fluid. Both must be selected together based on the chemical compatibility chart.

Metal bodies are cast and assembled with bolts or clamps, providing robust mechanical construction, impact resistance, and temperature tolerance. This is a suitable choice for outdoor use due to good UV resistance and temperature fluctuation tolerance, while also meeting grounding requirements and ATEX standards in areas with explosion risk.

• SS316 — meets FDA standards for food and cosmetics; resistant to a wide range of corrosive environments.
• Alloy C — used for highly aggressive corrosive fluids where stainless steel may not be sufficient.
• Aluminum — a cost-effective solution for general industry, lighter than cast iron or stainless steel.
• Cast iron — suitable when the fluid has high abrasive content.

Metal versions also meet high-pressure applications exceeding 125 psi (≈8.6 bar) such as in mining or long pipeline systems. A practical example from Sandpiper documentation: the 3″ S30 series stainless steel pump is used to transfer lithium carbonate extract in battery production.

Plastic bodies are bolted together, lightweight, easy to move, and typically lower in cost than metal versions. The primary strength is a broad chemical resistance spectrum, particularly for corrosive fluids where metals may fall short. In return, plastics are generally not UV-stabilized, limiting prolonged sun exposure, and are susceptible to damage from freezing — therefore indoor or controlled-environment installation is preferred.

• Polypropylene (PP) — suitable for strongly corrosive alkaline/caustic fluids.
• Conductive PP — handles corrosive chemicals with grounding requirements.
• Conductive PVDF — aggressive chemicals with abrasive particles, with grounding.
• PVDF Kynar — better abrasion resistance for aggressive chemicals.

!Plastic bodies are not UV-stabilized — prolonged sun exposure or freezing temperatures can cause damage. For outdoor installation in hot sunny provinces or cold storage facilities, consider a metal body or provide adequate shielding.

Note: the table above provides general material group guidance only. For each specific chemical (concentration, temperature, solids content), always consult the manufacturer’s chemical compatibility chart before finalizing the configuration.

• Step 1 — Fluid properties: identify corrosiveness, concentration, solids/abrasive content, and viscosity to narrow down between metal and plastic.
• Step 2 — Chemical compatibility: cross-reference the manufacturer’s “Chem Guide” for body, diaphragm, and ball valve materials.
• Step 3 — Installation environment: indoor or outdoor, ATEX/grounding requirements, operating temperature and pressure.
• Step 4 — Diaphragm & valve material: select diaphragm (PTFE/Santoprene/EPDM…) and valve type (ball or flap valve) appropriate for the fluid and solids content.

If reducing compressed air consumption is a goal, consider an electric diaphragm pump (EODD / electric diaphragm) — retaining the AODD advantages while reducing air consumption, suitable for continuous operation.