The diaphragm is the heart of every air-operated diaphragm pump – and its most important wear part. The right material determines service life, chemical resistance and operating costs. This guide introduces the common diaphragm materials and shows which one suits which fluid.
The materials at a glance
PTFE – the chemical all-rounder
PTFE is resistant to almost all chemicals: strong acids and alkalis, solvents, aromatics. PTFE diaphragms are usually combined with an elastomer back-up diaphragm. First choice for aggressive fluids, chemicals and pharmaceuticals – with somewhat lower flex resistance than pure elastomers.
Santoprene® – the rugged standard
This thermoplastic elastomer offers very good flex life and broad resistance to acids and alkalis. The economical standard for wastewater, slurries and many aqueous fluids; also available in an FDA-compliant version.
Buna-N (NBR) – for oils and greases
The classic material for mineral oil-based fluids: oils, greases, fuels, emulsions. Inexpensive and abrasion-resistant, but not suitable for ketones, strong acids or aromatics.
EPDM – for alkalis and low temperatures
EPDM is strong against alkalis, many dilute acids and hot water and remains flexible even at low temperatures. Not suitable for oils, greases and hydrocarbons.
FKM – for heat and aromatics
Fluoroelastomer withstands high temperatures and is resistant to aromatics, fuels and many concentrated chemicals. Ideal when temperature and chemicals come together; unsuitable for strong alkalis and ketones.
Hytrel® – the wear specialist
This thermoplastic polyester elastomer stands out with high abrasion and flex resistance with oils, fuels and abrasive fluids – often the longest-lasting choice for heavy-wear applications in the neutral pH range.
Overview table
| Material |
Well suited for |
Not suitable for |
| PTFE |
Strong acids and alkalis, solvents, aromatics |
Applications needing maximum flex life |
| Santoprene® |
Wastewater, slurries, aqueous fluids, acids and alkalis |
Many solvents and oils |
| Buna-N (NBR) |
Oils, greases, fuels, emulsions |
Ketones, strong acids, aromatics |
| EPDM |
Alkalis, dilute acids, hot water, low temperatures |
Oils, greases, hydrocarbons |
| FKM |
High temperatures, aromatics, fuels, concentrated chemicals |
Strong alkalis, ketones |
| Hytrel® |
Oils, fuels, abrasive fluids (neutral pH) |
Strong acids and alkalis |
The table is a guide only. Always check your fluid including concentration and temperature.
Selection in three steps
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Check chemical resistance: Check the fluid (including concentration and temperature) against the material – if in doubt with our chemical compatibility check.
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Assess the mechanics: Abrasive solids call for Santoprene® or Hytrel®; pure chemical resistance for PTFE.
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Observe requirements: Food and pharmaceutical applications require FDA-compliant materials (PTFE, FDA Santoprene®) – suitable pumps can be found under FDA diaphragm pumps; for hazardous areas, the requirements of the ATEX versions also apply.
Diaphragm replacement and spare parts
Diaphragms are wear parts: replacing them in good time protects against unplanned downtime. Original diaphragms in all materials and complete repair kits can be found in our spare parts section – available from stock. Not sure which one fits? Our technical team will identify the right diaphragm from the part number or nameplate.
