API · ASME · DIN · EN standard industrial valves
Diaphragm Valves
Valves sealing through a flexible diaphragm, built around sealing reliability in corrosive, slurry and utility service.
Last updated: 2026-10
Family specifications
| body materials | Cast iron (ASTM A126), Ductile iron (ASTM A536), WCB (ASTM A216), LCB (ASTM A352), CF8, CF8M (ASTM A351), F316/F316L (ASTM A182), F51/2205 duplex (ASTM A182), WC6, WC9 alloy (ASTM A217) |
|---|---|
| design focus | Diaphragm fatigue life, uniform seating, chemical resistance, throttling stability, ease of diaphragm replacement |
| designs | Cast Iron Diaphragm Valve, Ductile Iron Diaphragm Valve |
| diaphragm selection factors | Temperature limits, Chemical resistance, Flexibility, Fatigue life |
| size range | DN15 to DN300 |
| pressure class | PN10/PN16 (DIN), PN6 to PN16, Class 150 (ANSI) |
| temperature range | -20 to 250°C (PTFE-lined weir and straight-through) |
| design standards | BS 5156, BS 6755, ASME B16.5, BS 4505, EN 1092 |
| weir vs straight through pressure | Weir type: higher operating pressures, best for throttling duty, Straight-through: lower pressure rating, full bore, for high-solids and viscous media |
| hermetic isolation | Only two components contact the operating medium — the shut-off diaphragm and the valve body; actuator and medium are hermetically separated, so no stem seal/gland packing is required |
| weir design function | Weir seats the diaphragm with a compressible meniscus pad that minimizes cavitation and noise; best throttling control in the family with a higher flow coefficient; mountable in any position |
| diaphragm material temperatures | EPDM: -30 to +300 F; excellent water/steam/dilute acids-alkalis; poor oil resistance; intermittent steam sterilization, Neoprene: -20 to +200 F; wastewater, mildly acidic/alkaline media, entrained oils, Soft natural rubber: -30 to +180 F; best abrasion resistance for abrasive slurries, Viton (FKM): -20 to +300 F; oils, mineral acids, salt solutions, chlorinated hydrocarbons; not ammonia or polar solvents, TFE (Teflon)-faced / EPDM backing: -30 to +300 F; most chemical resistant; greater closing force, shorter working life, Butyl (IIR): -20 to +250 F; very low gas permeability — vacuum and gas service; dilute mineral acids, alkalis, water |
| diaphragm body materials | Cast iron ASTM A-126 Class B, Ductile iron ASTM A-536 Grade 65-45-12, Cast steel ASTM A216 Gr WCB, 316 stainless ASTM A-351 CF8M, Alloy 20 ASTM A-351 CN-7M |
| body linings available | Hard rubber / graphite-filled hard rubber (to 250 F), EPDM, Neoprene, Buna-N (to 275 F), Butyl, Chlorobutyl (to 180 F), Fluoropolymers: PTFE, PFA, FEP, PVDF, ETFE, ECTFE (to 350 F), Glass, polypropylene, polyurethane, PVC |
| weir buildup limitation | Weir recesses trap media against the diaphragm ("dead stops created from the build-up of media getting stuck around its diaphragm") — solidifying or crystallising media can delay shut-off; straight-through bore avoids this |
| diaphragm replacement interval | Typical maintenance guidance, not a fixed service life: the diaphragm is the wear component, and replacing rubber diaphragms roughly every 2-3 years and PTFE diaphragms every 4-5 years extends valve life beyond leaving the diaphragm to fail in service — actual life depends on cycling frequency, medium, temperature and duty, so treat the intervals as inspection anchors |
| hygienic diaphragm grades | Hygienic/pharma builds use USP Class VI and FDA-compliant EPDM, FPM, and PTFE diaphragms; elastomer and PTFE diaphragms are interchangeable on the same actuator, in hygienic sizes around DN10-100 |
Temperature: three separate dimensions
The whole-valve working temperature is set by the most limited component in the chosen combination — check the body lining limit and the diaphragm limit against the medium separately; neither number alone describes the valve.
| Whole-valve working temperature | -20 to 250°C (PTFE-lined weir and straight-through) |
|---|---|
| Body lining temperature limits |
|
| Diaphragm material | Temperature range | Chemistry and limits |
|---|---|---|
| EPDM | -30 to +300 F | excellent water/steam/dilute acids-alkalis; poor oil resistance; intermittent steam sterilization |
| Neoprene | -20 to +200 F | wastewater, mildly acidic/alkaline media, entrained oils |
| Soft natural rubber | -30 to +180 F | best abrasion resistance for abrasive slurries |
| Viton (FKM) | -20 to +300 F | oils, mineral acids, salt solutions, chlorinated hydrocarbons; not ammonia or polar solvents |
| TFE (Teflon)-faced / EPDM backing | -30 to +300 F | most chemical resistant; greater closing force, shorter working life |
| Butyl (IIR) | -20 to +250 F | very low gas permeability — vacuum and gas service; dilute mineral acids, alkalis, water |
Materials by part
Materials are listed per part because each part sees the medium differently — the lining and the diaphragm carry the chemistry, the body and disc carry the pressure and abrasion duty. Parts without published data for this family are omitted.
| Body | Cast iron (ASTM A126), Ductile iron (ASTM A536), WCB (ASTM A216), LCB (ASTM A352), CF8, CF8M (ASTM A351), F316/F316L (ASTM A182), F51/2205 duplex (ASTM A182), WC6, WC9 alloy (ASTM A217), Ductile Iron / GGG50, Cast Iron, Ductile Iron, WCB |
|---|---|
| Stem | Stainless Steel 304 |
| Disc | Cast Iron, Ductile Iron, WCB |
| Lining | Hard rubber / graphite-filled hard rubber (to 250 F), EPDM, Neoprene, Buna-N (to 275 F), Butyl, Chlorobutyl (to 180 F), Fluoropolymers: PTFE, PFA, FEP, PVDF, ETFE, ECTFE (to 350 F), Glass, polypropylene, polyurethane, PVC, NBR, EPDM |
| Diaphragm | EPDM, Neoprene, Soft natural rubber, Viton (FKM), TFE (Teflon)-faced / EPDM backing, Butyl (IIR), NBR |
Weir vs straight-through: choosing the body pattern
| Dimension | Weir type | Straight-through |
|---|---|---|
| Flow path | Contoured weir seat — the diaphragm presses onto the weir through a compressible pad; mountable in any position | Full, unrestricted bore — the diaphragm seals against a straight-through body |
| Operating pressure | Generally handles higher operating pressures in this family | Lower operating-pressure rating than the weir type |
| Throttling | Best throttling control in the family; the seated pad minimizes cavitation and noise with a higher flow coefficient | Not the throttling choice — used where unrestricted flow matters more than control |
| Solids and viscosity | Suits lower-solids duties; media can settle around the weir | Handles much higher solid content, greater fluid viscosity, and media needing an unrestricted bore |
| Solidifying or crystallising media | Weir recesses can trap build-up against the diaphragm, delaying shut-off — avoid for these media | The full bore avoids trapping, so solidifying media pass through |
| Media isolation | Only the diaphragm and the body lining contact the medium; the actuator is hermetically separated | Same two-component media contact — the hermetic separation applies to both body patterns |
Diaphragm material selection guide
| Material | Temperature range | Chemistry and limits |
|---|---|---|
| EPDM | -30 to +300 F | excellent water/steam/dilute acids-alkalis; poor oil resistance; intermittent steam sterilization |
| Neoprene | -20 to +200 F | wastewater, mildly acidic/alkaline media, entrained oils |
| Soft natural rubber | -30 to +180 F | best abrasion resistance for abrasive slurries |
| Viton (FKM) | -20 to +300 F | oils, mineral acids, salt solutions, chlorinated hydrocarbons; not ammonia or polar solvents |
| TFE (Teflon)-faced / EPDM backing | -30 to +300 F | most chemical resistant; greater closing force, shorter working life |
| Butyl (IIR) | -20 to +250 F | very low gas permeability — vacuum and gas service; dilute mineral acids, alkalis, water |
Hygienic/pharma builds use USP Class VI and FDA-compliant EPDM, FPM, and PTFE diaphragms; elastomer and PTFE diaphragms are interchangeable on the same actuator, in hygienic sizes around DN10-100
Maintenance guidance
Typical maintenance guidance, not a fixed service life: the diaphragm is the wear component, and replacing rubber diaphragms roughly every 2-3 years and PTFE diaphragms every 4-5 years extends valve life beyond leaving the diaphragm to fail in service — actual life depends on cycling frequency, medium, temperature and duty, so treat the intervals as inspection anchors
Ordering & documentation
Documents
The documentation checklist in the Applications & procurement guide below lists what to attach to the inquiry and what to request with the order; certificate availability is confirmed at quotation.
Quotation
Send the medium, temperature, pressure, size and connection for a quotation-ready inquiry. Lead time, MOQ and price are confirmed at quotation, together with the documents to be supplied with the order.
Storage & shipping
Diaphragm valves are rubber- or PTFE-lined products — storage limits and shipping arrangements for the selected lining and diaphragm materials are confirmed at quotation.
Frequently asked questions
Weir or straight-through — which body pattern suits my media?
Weir bodies take the higher operating pressures and give the best throttling control. Straight-through bodies trade pressure rating for a full bore that passes high-solids, viscous or solidifying media without trapping — the safe choice when media crystallise or build up.
Which temperature limit applies to a diaphragm valve?
Three of them, and the lowest governs: the body lining limit, the diaphragm material limit, and the assembled whole-valve working temperature (-20 to 250°C (PTFE-lined weir and straight-through)). Check the lining and the diaphragm against the medium separately.
How often should the diaphragm be replaced?
Typical maintenance guidance, not a fixed service life: the diaphragm is the wear component, and replacing rubber diaphragms roughly every 2-3 years and PTFE diaphragms every 4-5 years extends valve life beyond leaving the diaphragm to fail in service — actual life depends on cycling frequency, medium, temperature and duty, so treat the intervals as inspection anchors
Applications & procurement guide
Application
Water treatment and effluent
The standard duty for cast iron and ductile iron bodies: water treatment, effluent handling and low-pressure utility lines, with weir bodies taking the higher pressures of these networks.
Application
Chemical and corrosive media
Because only the diaphragm and the body lining ever contact the medium, chemistry is chosen layer by layer — rubber or fluoropolymer linings from hard rubber through PTFE, PFA, FEP, PVDF, ECTFE to glass, matched against the diaphragm material window for the specific media.
Application
Slurries and high-solids media
Soft natural rubber diaphragms give the best abrasion resistance for abrasive slurries, and straight-through bodies pass high solid content and viscous media that would settle and trap around a weir.
Application
Food, pharmaceutical and hygienic
Hermetic separation between actuator and medium suits hygienic service; USP Class VI and FDA-compliant EPDM, FPM and PTFE diaphragm grades are available, with elastomer and PTFE diaphragms interchangeable on the same actuator in hygienic sizes around DN10-100.
What to tell us when you inquire
- Medium and concentration (and whether solids, crystals or particles are present)
- Operating temperature — normal range plus excursions
- Operating and shut-off pressure
- Valve size, end connection and governing standard (e.g. BS 5156, EN 1092, DIN)
- Lining and diaphragm material preference — or the duty description so materials can be proposed
- Body pattern: weir or straight-through, if the duty dictates one
- Actuation: manual, electric or pneumatic (and fail-safe requirements)
Documents to prepare or request
- Line data sheet or P&ID extract for the valve position
- Media safety data sheet when chemistry is non-standard
- Diaphragm material compliance certificates where required (e.g. FDA, USP Class VI for hygienic builds)
- Applicable design and testing standards to be met
- Dimensioned requirements: face-to-face, flange table, actuator envelope
Knowledge: selection guides
Types in this family
Type
Cast Iron Diaphragm Valves
Cast iron diaphragm valves isolate or throttle utility flows by pressing a flexible diaphragm against a weir, so the wetted metal stays out of the medium — the
View specifications →Type
Ductile Iron Diaphragm Valves
Ductile iron diaphragm valves put a higher-strength body behind the same weir-sealing idea: a flexible diaphragm meets a body weir so the elastomer and lining —
View specifications →Type
Weir-Type Diaphragm Valves
Weir-type diaphragm valves seal the flexible diaphragm against a raised weir built into the body, so the short stroke and supported diaphragm suit throttling an
View specifications →Type
Straight-Through Diaphragm Valves
Straight-through diaphragm valves run the flow path through an unobstructed, nearly straight bore that the flexible diaphragm presses down onto, so viscous medi
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