Corrosion-Resistant Diaphragm Valve — WCB Body with PFA Lining, ANSI 150 Flange, ½" to 4"

The corrosion-resistant diaphragm valve with PFA lining is fundamentally different from all ball, butterfly, and globe valves in the catalog in one decisive aspect: the only moving component that touches the fluid is the flexible diaphragm — there is no stem, ball, or obturator exposed to the aggressive fluid. The metal stem pushes the diaphragm from the outside against the body weir to close, and releases it to open, but never penetrates the fluid space. This complete separation between the operating mechanism and the aggressive fluid is the fundamental advantage of the diaphragm valve for services involving concentrated acids, strong oxidizers, and high-purity fluids.

The diaphragm is a two-layer construction: an EPDM core that provides the elasticity and recovery force needed to repeatedly seal and open, with an outer face of PFA (or FEP) which is the only surface in contact with the fluid — resistant to virtually all acids, alkalis, and oxidizers that would destroy any conventional elastomer. The WCB body with PFA internal lining completes the total protection of the metal.

Why the diaphragm valve is different from the ball valve for aggressive fluids

Both the PFA corrosion-resistant ball valve and the PFA corrosion-resistant diaphragm valve handle extreme corrosive fluids — but they have distinct technical advantages that determine when to use each:

The double EPDM + PFA diaphragm — how it works

The diaphragm is the technical heart of this valve. The two-layer construction solves the fundamental problem of single-material diaphragms:

• Inner face (in contact with fluid) — PFA/FEP: The PFA or FEP fluoropolymer on the diaphragm face that touches the fluid provides practically universal chemical resistance — compatible with HF, concentrated H₂SO₄, concentrated HCl, ClO₂, H₂O₂, and virtually any strong acid, alkali, or oxidizer. PFA does not degrade, swell, or release any compounds into the fluid — essential in high-purity applications.
• Outer face (in contact with mechanism) — EPDM: The EPDM core provides the elasticity and recovery force necessary for the diaphragm to seal tightly against the weir when closing and regain its shape correctly when opening. A pure PFA diaphragm would be too rigid for this flexing cycle — EPDM is the correct material for mechanical support.
• Result: A diaphragm that has the chemical resistance of PFA where it matters (the face touching the fluid) and the elasticity of EPDM where it is needed (the mechanical support for the flexing cycle).

Weir-type body — non-turbulent flow

The Weir-type diaphragm valve (raised weir) has a central protrusion in the body — the weir — against which the diaphragm rests when closing. The fluid passes beneath the weir and to the sides in the open position, generating a smooth, non-turbulent flow. Specific advantages of the Weir type:

• Laminar flow without turbulence: The flow profile does not generate cavitation or erosion in the diaphragm — significantly extends the service life of the diaphragm compared to through-way designs that generate direct turbulence on the diaphragm.
• Short diaphragm stroke: The diaphragm travels a short distance between open and closed positions — less material fatigue from flexing cycles.
• No significant dead zones: The Weir-type body has less residual fluid accumulation than the through-way type — advantageous for fluids that crystallize or solidify upon cooling.
• Suitable for modulating control: The Weir's flow characteristic is approximately linear — the diaphragm can be positioned at any point between open and closed to regulate flow.

Valve components — complete material table

Technical Specifications

• Type: Weir Diaphragm (raised weir)
• Design standard: MSS-SP-88
• Face to face: EN 558-1
• Flanges: ASME/ANSI B16.5 — ANSI 150 RF
• Inspection and testing: API 598
• Body material: A216 WCB + PFA interior lining
• Diaphragm: PFA/FEP (inner face) + EPDM (support)
• Stem: SS420 — does not penetrate the fluid space
• Nominal diameters: ½" (DN15), ¾" (DN20), 1" (DN25), 1¼" (DN32), 1½" (DN40), 2" (DN50), 2½" (DN65), 3" (DN80), 4" (DN100)
• Maximum pressure: 285–290 psi (19.6–20 bar) at 38 °C — reduces with temperature according to ASME B16.34
• Operating temperature: -30 °C to +200 °C — verify specific fluid concentration and temperature
• Flow characteristic: 1Cv = 1.167Kv — approximately linear flow characteristic
• Standard operation: Manual with ergonomic handwheel
• Vacuum capability: Yes — suitable for vacuum service

Chemical compatibility confirmed in technical sheet

• ✅ Hydrochloric acid HCl — any concentration
• ✅ Nitric acid HNO₃ — including concentrated
• ✅ Hydrofluoric acid HF — any concentration
• ✅ Liquid chlorine Cl₂
• ✅ Sulfuric acid H₂SO₄ — including concentrated
• ✅ Sodium hypochlorite NaClO — any concentration
• ✅ Peroxides (H₂O₂ and other oxidizers)
• ✅ Concentrated alkalis (NaOH, KOH)
• ✅ Highly aggressive organic solvents
• ✅ Extremely high purity fluids — no metal leaching
• ⚠️ Always verify specific process concentration and temperature — compatibility may vary under extreme conditions

Main applications

• Chemical and petrochemical industry — concentrated acids: Isolation and flow control in lines for HF, concentrated H₂SO₄, concentrated HCl, HNO₃, and their mixtures. The absence of a stem in the fluid eliminates the most frequent leak point in process valves with extreme corrosive fluids.
• Chlorine, hypochlorite, and oxidizer processes: Distribution of liquid chlorine, high-concentration sodium hypochlorite, and peroxides in water treatment plants, paper bleaching, and chemical synthesis. The PFA diaphragm resists the aggressive oxidation of these fluids indefinitely.
• Pharmaceutical industry — high purity: Control of synthesis fluids, process solvents, and acidic solutions in pharmaceutical plants where metallic fluid contamination is unacceptable. PFA has practically zero leaching — it does not release any compounds into the fluid.
• Semiconductors and ultrapure water (UPW): Control of etching acid mixtures, ultrapure water distribution, and process fluids in integrated circuit and flat panel display manufacturing. PFA is the standard material in the semiconductor industry due to its purity and chemical resistance.
• Mining — SX-EW and acid leaching: Control of concentrated H₂SO₄ electrolyte in copper electrowinning cells, acid leaching solutions, and flotation reagents. The PFA diaphragm valve resists aggressive electrolyte better than any valve with an exposed metallic stem.
• Water treatment — ClO₂ and chlorine disinfection: Control of chlorine dioxide, dissolved gaseous chlorine, and hypochlorite in water treatment plants using these disinfectants. PFA resists concentrations that would destroy SS316 in weeks.
• Crystallizing or sticky fluids: The smooth PFA inner lining prevents the adhesion of crystals and solids that would accumulate in the cavities of a ball or butterfly valve — facilitating cleaning and preventing valve blockage.
• Paper, ink, pigment, and coating manufacturing: Control of bleaching solutions, acidic pigments, and aggressive solvent coatings where the smooth PFA surface prevents scaling and simplifies cleaning between batches.

Diaphragm valve automation

The standard version includes manual operation with an ergonomic handwheel. For automation, the diaphragm valve is compatible with linear pneumatic actuators that replace the handwheel — the actuator pushes and releases the diaphragm with the same linear action as the manual handwheel. Specific considerations:

• NC linear pneumatic actuator: For hazardous fluids (HF, ClO₂, concentrated H₂SO₄), automatic spring closure upon air supply loss is the safety standard. The single-acting NC linear pneumatic actuator is the most common configuration.
• Modulating control: The Weir's linear flow characteristic allows proportional flow control with a 4–20 mA electropneumatic positioner — the diaphragm valve is suitable for PID control loops in corrosive fluids where a globe valve would have chemical compatibility issues.
• Actuator material in acidic vapors: Specify an actuator with an SS316 casing or a high chemical resistance epoxy coating — standard anodized aluminum would corrode in environments with HF or HCl vapors.

For the complete range of corrosion-resistant valves, see PFA corrosion-resistant valves category →

Technical Data Sheet