WCB Knife Gate Valve with EPDM Seat — Bidirectional, Ultrathin Body, 2" to 12"

The WCB knife gate valve with EPDM seat is the most abrasion-resistant variant of the Cematic knife gate family — its internal EPDM rubber lining protects all internal metal surfaces against erosion from solid particles, tailings, and abrasive slurries that would directly wear down metal in unlined versions. Unlike unidirectional knife gates, this model is bidirectional — the blade seals tightly in both flow directions, simplifying installation by eliminating the risk of mounting the valve in the wrong direction. The ultrathin two-piece wafer body design is more compact than high-yoke designs — an advantage in installations with limited axial space between equipment.

The EPDM seat — elastic protection against abrasive particles

The EPDM seat in a knife gate valve serves a different function than the PTFE or metal seats of previous versions:

• Elastic protective lining: EPDM is not just the sealing element — it lines the contact area between the blade and the body, absorbing the impact of abrasive particles traveling in the flow. Instead of hard particles directly hitting the metal of the seat, they first impact the EPDM elastomer, which absorbs and distributes the impact energy.
• Bidirectional sealing: The elasticity of EPDM allows the seat to adapt to micro-irregularities on both faces of the blade surface — providing tight sealing regardless of pressure direction. Rigid PTFE requires a more precise seat geometry to seal in both directions.
• Self-cleaning by elasticity: Elastic EPDM tends to expel solid particles lodged between the seat and the blade during opening and closing movements — the elastic deformation of the seat as the blade passes pushes particles out of the sealing area.
• Operating temperature up to 110 °C: EPDM is the correct material for hot water, moderate-temperature process slurries, and aqueous fluids up to 110 °C. Above this limit, versions with PTFE or metal seats (up to 180 °C) are the correct specification.

Bidirectional — simplifies installation and specification

Unidirectional knife gate valves have a flow direction indicated on the body and must be installed correctly to seal. The bidirectional valve eliminates this restriction:

• No critical flow direction: The valve seals in both directions — the installer does not need to check flow orientation before mounting the valve.
• Protection against back pressure: In lines where pressure can exist in both directions (pumping systems with potential for reversal, bidirectional bypasses), the bidirectional valve seals correctly in any scenario.
• Simpler specification: By not requiring flow direction indication, the technical specification of the project is simpler, and the risk of installation errors in the field is eliminated.

Ultrathin two-piece body

The ultrathin body design (minimum face-to-face according to dimension table) with two-piece construction differentiates this valve from the conventional high-yoke design:

• Smaller axial space: The 58–90 mm face-to-face (depending on diameter) is significantly smaller than that of high-yoke knife gates — a more compact valve that takes up less space in the line.
• Lower weight: Without a tall structural yoke, the valve weighs considerably less than versions with a yoke — an advantage in aerial installations and structures with load limitations.
• Installation between standard flanges: The ultrathin profile allows installation in spaces where high-yoke knife gates would not fit.

Valve Components

Technical Specifications

• Type: Bidirectional Knife Gate — vertical linear motion
• Body Design: Two-piece, ultrathin
• Installation: Between flanges — Class 150LB
• Body Material: WCB (ASTM A216 Gr. WCB)
• Disk (Blade): SS304
• Seat: EPDM
• Gasket: EPDM
• Packing: EPDM
• Stem: 2Cr13 (Martensitic Stainless Steel)
• Operation: Manual with malleable cast iron handwheel
• Nominal Diameters: 2" (DN50), 3" (DN80), 4" (DN100), 6" (DN150), 8" (DN200), 10" (DN250), 12" (DN300)
• Maximum Pressure: 290 psi (20 bar) at 38 °C — reduced with temperature according to ASME B16.34/B16.5
• Seat Test Pressure: 0.8 MPa (8 bar)
• Operating Temperature: -20 °C to +110 °C
• Flow Direction: Bidirectional

Comparison — Four Cematic Knife Gates

Fluid Compatibility

• ✅ Non-corrosive municipal and industrial wastewater
• ✅ Primary and secondary WWTP sludges
• ✅ Mineral tailings and abrasive slurries
• ✅ Fly ash and limestone slurries in thermal power plants
• ✅ Cement, clinker, and slag mixtures in the cement industry
• ✅ Viscous fluids with non-corrosive suspended solids
• ✅ Anaerobic digestion sludges up to 55 °C
• ⚠️ Fluids with high chlorides or H₂S: WCB body may corrode — use SS316
• ⚠️ Temperature above 110 °C: use knife gate with PTFE or metal seat
• ❌ Corrosive fluids (acids, alkalis): use SS316 or PFA anti-corrosive knife gate

Main Applications

• Mining — abrasive tailings and slurries: The most demanding application for any knife gate valve. Mineral tailings (30–70% solids, quartz, silica, and hard mineral particles) rapidly erode bare metal. The EPDM lining absorbs abrasive impacts and extends the lifespan of internal surfaces. The bidirectional nature is particularly valuable in tailings circuits where flow direction can vary depending on pump operation.
• Thermal power plants — ash and desulfurization slurries: Hydraulic transport of fly ash, limestone slurries (FGD), and slag suspensions are the most abrasive fluids in the energy industry. The EPDM of the seat protects the metal parts of the WCB from the continuous impact of fine ash and slag particles.
• Cement industry: Flow control of cement mixtures, clinker slurries, and slag in cement production facilities. The abrasiveness of these mixtures requires elastomeric protection of the seat — EPDM is the standard material for these services.
• Wastewater treatment plants — municipal sludges: Isolation of primary, secondary, and digested sludge lines in municipal WWTPs. Bidirectionality simplifies project installation and specification — no risk of incorrect mounting.
• Pulp and paper — pulp and sludge lines: Flow control of cellulose pulp and process sludges in paper mills. The high abrasion resistance of EPDM significantly extends the lifespan of the seat against fibers and particles in the pulp.
• Chemical processes with non-corrosive solids: Process fluids with suspended particles where the fluid's corrosivity does not exceed WCB's resistance — solid catalysts, pigments, process additives, and reactant mixtures with solids.

For sludges with higher chemical aggressiveness, see SS316 knife gate valve →

Technical Data Sheet