Product Range
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Wafer Knife Gate Valve
Quick Specs 2" - 24" (DN50 - DN600) Class 150 (up to 10 bar / 150 psi) MSS SP-81, ASME B16.34 A216 WCB, A351 CF8M, A351 CF8 Soft rubber (EPDM/NBR), PTFE-lined, metal-to-metal Wafer (lug) body, bonnetless, single-piece gate, unidirectional sealing, thin body profile between flanges Why Wafer? Because Space Costs Money Some plants pack pipe into tunnels so tight you can barely reach your hand between two flanges. That's where the wafer knife gate valve earns its spot. No flange ends on the body—it sandwiches straight between your pipeline flanges, held in place by the bolting that runs through the lug holes. The result? A face-to-face dimension that's barely wider than the gate itself. I've seen installation crews drop a 12-inch wafer knife gate into a paper mill's digester feed line in under twenty minutes. Same size flanged body? They'd still be wrestling with bolting and alignment. The slim profile isn't just convenient—it's the reason this valve exists. The Price Advantage Is Not A Marketing Line A wafer body costs 30-40% less than a flanged equivalent at the same diameter. That's not a rounding error. The body casting is smaller, the machining is simpler, there are fewer surfaces to finish. If you're buying twenty valves for a water treatment plant upgrade, that difference adds up to real budget room. But—and this matters—the savings come with a trade-off. Wafer knife gates seal in one direction only. The gate pushes against a single seat. Flow comes from the upstream side, pressure drives the gate into the seat pocket, and you get a tight seal. Reverse that flow direction, and the seat can't hold. If your process needs bidirectional shutoff, this isn't your valve. Walk over to the dual-seat designs instead. What The Seat Options Mean In Practice EPDM seats handle clean water and dilute chemical service. NBR is your pick for oils and hydrocarbon traces. PTFE-lined seats step up when you need chemical resistance that rubber can't provide—think acid lines or solvent service. Metal-to-metal seats exist on the spec sheet, but honestly, if you're buying a wafer knife gate, you're usually in soft-seated territory. Metal seats belong on the high-pressure side of the family. Installation Notes From The Field Always confirm flow direction before you bolt a wafer knife gate into the line. The body is marked—usually an arrow cast into the casting or a tag on the bonnet area—but I've seen more than one plant run media backward through a unidirectional valve and then complain about leakage. That's not a valve failure. That's an installation error. Lug-style wafer bodies let you remove one side of the piping while the valve stays in place, which is handy for maintenance access on dead-end lines. Standard wafer (no lugs) requires both flanges to stay bolted to hold the valve. Know which one you're ordering. FAQ A: No. Class 150 rating and soft seats don't belong on steam service. Use a high-pressure knife gate with metal seats and a pressure seal bonnet for that application. A: Light slurry, yes—pulp stock, dilute mine tailings, wastewater with suspended solids. Heavy abrasive slurry will eat through soft rubber seats fast. Consider a polyurethane-lined knife gate for that duty. A: Lug wafer bodies have threaded holes that accept bolts from each flange independently. Standard wafer bodies have plain through-holes—bolts pass through the entire assembly. Lug style allows single-side pipe removal. A: Yes. Pneumatic and electric actuators mount to the valve bonnet area. Keep in mind that actuation adds height above the valve—check your vertical clearance in tight installations. A: The single-seat design only seals when flow pressure pushes the gate into the seat. Reverse flow lifts the gate off the seat. Any process line with potential backflow needs a bidirectional sealing design.
High Pressure Knife Gate Valve
Quick Specs 2" - 24" (DN50 - DN600) Class 300 - 900 (up to 150 bar / 2200 psi) ASME B16.34, API 600 A216 WCB, A217 WC6/WC9, A182 F316, A182 F51/F53 Metal-to-metal (Stellite 6 overlay), reinforced PTFE for lower pressure configurations Flanged or welded body, heavy-wall construction, pressure seal bonnet above Class 600, rising stem with OS&Y indicator, bidirectional sealing This Valve Exists Because Wafer Designs Blow Out Standard knife gate valves top out at Class 150. Push them past 10 bar and the thin wafer body starts to flex. Push them to 50 bar and you're gambling. At 150 bar? You're not gambling—you're planning a failure. The high-pressure knife gate valve solves this by being built like a block valve with a knife edge. Heavy-wall body casting. Flanged or welded ends—no wafer sandwich here. Above Class 600, the bonnet switches to a pressure seal design, where internal pressure actually compresses the bonnet seal ring tighter. Higher the pressure, tighter the seal. It's the same bonnet concept used on high-pressure gate valves in power plants and petrochemical steam systems. Stellite Seats Are Not Optional At This Level Metal-to-metal seating with Stellite 6 overlay is standard on the high-pressure configurations. Stellite resists galling, handles temperature cycles, and maintains seat integrity when the gate slams shut under full line pressure. Reinforced PTFE seats are available on Class 300 configurations for services where chemical resistance matters and pressure is moderate—but once you cross Class 600, it's metal seats all the way. I've replaced seats on knife gates that cycled twice daily on a high-pressure steam bypass line for three years without measurable wear on the Stellite overlay. That's the kind of longevity you pay for when you spec this valve. The OS&Y Stem Tells You What You Need To Know Rising stem with outside stem and yoke (OS&Y) indicator. You can look at the valve from across the plant floor and see whether it's open or closed—the stem position is visible, not hidden inside the body. On high-pressure lines, that visual confirmation matters. You don't want to guess whether a valve holding 100 bar of pressure is open or shut. The rising stem gives you that answer at a glance. Material Selection Matches The Service A216 WCB handles standard hydrocarbon and steam service up to about 425°C. WC6 and WC9 creep into higher temperature territory—creep-resistant alloys for sustained high-temp operation. A182 F316 gives you corrosion resistance on sour service or chloride environments. F51 and F53 duplex alloys bridge the gap between strength and corrosion resistance, particularly useful on offshore and subsea process lines where both properties matter simultaneously. FAQ A: At Class 900, rated pressure depends on the body material and temperature. Check ASME B16.34 pressure-temperature tables for your specific material and operating temperature. Some configurations reach 150 bar; not all go to 200 bar. A: Bolted bonnets rely on bolt tension to keep the bonnet gasket compressed. As pressure rises, internal force pushes the bonnet upward, working against the bolts. Pressure seal designs use internal pressure to compress the seal ring—higher pressure means a tighter seal. Above Class 600, pressure seal is the reliable choice. A: Yes. High-pressure knife gate valves use dual-seat or wrap-around seat designs that hold pressure from both directions. Unidirectional sealing is not acceptable at these pressure levels. A: Electric motor actuators are common on high-pressure knife gates for precise, repeatable positioning. Pneumatic cylinders work on Class 300-600 sizes. At Class 900, electric actuators with torque limiting are preferred—you need controlled seating force, not a pneumatic hammer stroke. A: Knife gate valves cut through suspended solids and pulp that would jam a standard gate valve's wedge. If your media is clean fluid, a standard gate valve is fine. If there's solids in the line, the knife gate's sharp edge is the functional advantage.
Knife Gate Valve Fully Lined with Polyurethane
Quick Specs 2" - 24" (DN50 - DN600) Class 150 - 300 (up to 20 bar / 300 psi) MSS SP-81, manufacturer-specific (no PU-lined valve API standard exists) Carbon steel (A216 WCB) body with full internal polyurethane lining Full-body polyurethane liner (shore hardness 80A-95A), gate coated with PU or hard chrome Wafer or flanged body, PU liner covers all wetted surfaces—body cavity, seat area, gate channel, bonnet bore. No metal-to-media contact inside the valve. The Wear Champion For Media That Eats Metal Mining operations, mineral processing plants, tailings transport pipelines—these aren't gentle on valves. The slurry carries rock fragments, silica, mineral concentrate, and whatever else the process grinds into suspension. That media flows through the valve at 2-3 m/s and abrades every surface it touches. Standard rubber seats last maybe three to six months on a hard-rock tailings line. Metal seats? Sometimes less, because the slurry doesn't just wear the seat—it scores the gate, erodes the body cavity edges, and turns the bonnet bore into a ragged channel. Polyurethane lining changes the economics entirely. PU's abrasion resistance is 5-10x better than hard rubber. That's not a lab number on a datasheet—it's what you see in actual service on concentrator lines running 18 hours a day. Full-Body Liner Means Zero Metal Contact This isn't a seat-pocket liner or a partial coating. The polyurethane liner covers every wetted surface inside the valve: the body cavity, the seat area, the gate channel where the blade travels, and the bonnet bore above the gate. When slurry enters the valve, it touches polyurethane—not carbon steel, not cast iron, not stainless. That matters for two reasons. First, abrasion resistance is uniform throughout the flow path. There are no exposed metal edges where erosion accelerates because the liner stops short. Second, the liner acts as a chemical barrier. Many mine slurries carry residual process chemicals—flocculants, lime, acid traces—that corrode bare metal over time. PU isolates the body structure from that chemical exposure entirely. Replace The Liner, Not The Valve When the liner wears through after two or three years of continuous service, you don't throw away the valve body. You replace the liner. The carbon steel shell is still structurally sound—it hasn't been in contact with the media, so there's no erosion, no corrosion, no fatigue from chemical attack. Liner replacement takes the valve offline for a shift, maybe a day. Replacing the entire valve body would take longer and cost five to ten times more. This is the economic argument that wins procurement decisions on mine sites. Total cost of ownership over a ten-year service life favors the PU-lined valve by a wide margin, even though the initial purchase price is higher than a bare metal knife gate. Shore Hardness Selection Depends On Your Slurry Shore 80A is softer—it flexes more, absorbs impact energy from larger rock particles, and provides better sealing on low-pressure lines. Shore 95A is harder—it resists fine-particle abrasion better and maintains seat geometry under higher pressure. Most mining applications land somewhere in the 85A-90A range. Talk to the manufacturer about your specific slurry composition, particle size distribution, and flow velocity. The right hardness choice extends liner life significantly. FAQ A: No. This product category falls under manufacturer-specific design standards. The body rating follows ASME B16.34 for pressure-temperature limits, but the liner design and performance criteria are established by individual manufacturers. A: Polyurethane resists most mining process chemicals including mild acid traces, lime, and flocculant residues. For strong acid service (pH below 3 sustained), verify chemical compatibility with the specific PU compound—some formulations degrade under prolonged acid exposure. A: Standard PU liners operate up to about 80°C continuously. Above that, the material softens and loses abrasion resistance. High-temperature PU formulations reach 100-120°C, but they're harder to source and cost more. A: Rubber lining works on less abrasive slurries. But on hard-rock and mineral concentrate lines, rubber wears through in months where PU lasts years. The 5-10x abrasion resistance advantage is real on these services. A: Minimal impact. The liner adds slight friction to gate travel, but the difference is negligible on pneumatically actuated valves. Handwheel-operated valves may feel slightly heavier to stroke on larger sizes.
Heavy-Duty (Long Pattern) Slurry Valve
Quick Specs 2" - 36" (DN50 - DN900) Class 150 - 300 (up to 20-50 bar depending on configuration) Manufacturer-specific design standards, ASME B16.34 body rating A216 WCB, ductile iron (A536 65-45-12), A351 CF8M Metal-to-metal with Stellite overlay, or elastomer-lined seat pocket Long-pattern body (extended face-to-face dimension compared to wafer), two-piece bolted body, full-port bore, heavy-duty gate with guiding ribs, OS&Y or pneumatic actuated Long Pattern Is Not Wafer With Extra Length Here's the misunderstanding I hear most often: "Long pattern is just a wafer knife gate with a longer body." It's not. The extended face-to-face dimension exists because slurry service demands internal space that a wafer body cannot physically provide. The gate needs a longer travel channel to clear the full bore without jamming. Slurry carries solids that pack into tight spaces—a short gate channel on a wafer body fills with debris, the gate sticks, and you're cycling the actuator repeatedly to force it through. The long pattern gives the gate a clean travel path with room for solids to move out of the way rather than compressing into the channel. The seat pocket needs depth. Elastomer inserts for slurry isolation require enough pocket volume to maintain their shape under line pressure and abrasive flow. Shallow wafer-type seat pockets deform under sustained service. The long pattern body provides the structural depth for stable seat geometry. The body wall needs thickness for survival. Slurry at 2-3 m/s erodes internal surfaces continuously. A thin wafer body wall is adequate for clean water. It's inadequate for media that removes metal by the millimeter per year. Two-Piece Bolted Body—Serviceability That Counts The two-piece bolted body splits along a horizontal joint. You can open the body, inspect the seat, clean the gate channel, and replace worn components without cutting the valve out of the line on smaller installations. On larger sizes where line removal is necessary, the bolted joint still saves time—the body separates for internal access without welding or cutting. This is a practical advantage on mine sites and processing plants where valve service windows are short and maintenance crews work against the clock. Full-Port Bore Keeps Slurry Moving The bore matches the pipeline diameter with no reduction. Slurry doesn't tolerate velocity changes well—narrowing the bore accelerates flow, increases erosion, and creates turbulence that packs solids into the seat area. Full-port design maintains consistent flow velocity through the valve, which reduces both seat wear and the risk of solids settling in the body cavity when the valve is partially open. Gate Guiding Ribs Prevent Wander The gate on a long pattern slurry valve isn't a flat blade hanging free in the channel. Guiding ribs on the gate engage with slots or channels in the body, keeping the blade aligned throughout its travel stroke. On heavy slurry lines, lateral forces from flow and solids loading push the gate sideways. Without guiding ribs, the gate can deflect enough to miss the seat entirely on closure. The ribs prevent that. FAQ A: Wafer bodies don't have the internal depth for proper seat pocket design, gate guiding, or the wall thickness needed for sustained abrasive service. On light slurry, wafer works. On heavy slurry, long pattern is the correct specification. A: Up to 36 inches (DN900) on some manufacturer ranges. Large sizes typically use flanged body construction with pneumatic actuation—handwheel operation on a 36-inch slurry valve requires more torque than one person can reasonably apply. A: Ductile iron (A536 65-45-12) is cost-effective and structurally adequate for Class 150 slurry service on non-critical lines. Carbon steel (A216 WCB) is the choice when you need higher pressure rating, welding compatibility, or compliance with plant specifications that mandate steel bodies. A: You can, but it's overspecified. Clean water doesn't need the extended gate channel, heavy wall thickness, or seat pocket depth that slurry demands. A standard wafer knife gate is more economical for that service. A: Neither is "standard"—it depends on your installation. OS&Y works for manual isolation points with infrequent cycling. Pneumatic actuation is the right choice for automated process lines, remote valve stations, and applications requiring fast, repeatable stroke timing.
Pneumatic Bidirectional Sealing Knife Gate Valve
Quick Specs 2" - 24" (DN50 - DN600) Class 150 - 300 (up to 20 bar / 300 psi) MSS SP-81, manufacturer-specific bidirectional design A216 WCB, A351 CF8M, A351 CF8, ductile iron Dual-seat arrangement (upstream + downstream), elastomer (EPDM/NBR/Viton) or metal with Stellite overlay Two-piece bolted body, U-shape or peripheral dual-seat pocket, pneumatic cylinder actuator (single-acting spring-return or double-acting), bidirectional zero-leakage shutoff Bidirectional Sealing—And Why You Need It Most knife gate valves seal in one direction. Flow pushes the gate into the seat, the seat compresses, and you get a tight seal. Reverse the flow and the gate lifts off the seat. Pressure escapes. On process lines that only flow one way, that's fine. But plenty of real-world process lines have pressure on both sides of the valve. Consider a tank isolation valve where the tank head pushes one way and the pipeline pressure pushes the other. Consider a pump bypass line where you need to isolate against backpressure from the downstream system. Consider any loop circuit where flow direction reverses depending on which pump is running. In all these cases, a unidirectional knife gate leaks in reverse flow—not because the valve is defective, but because the single-seat design physically can't hold pressure from the wrong direction. Bidirectional sealing solves this with two independent seat arrangements. One seat seals when flow pushes the gate forward. The other seat seals when flow pushes the gate backward. Neither direction gets a free pass. The U-Shape Seat Wraps Around The Gate Edge The most common bidirectional seat design is the U-shape or peripheral seat pocket. The elastomer or metal seat forms a channel that wraps around the bottom edge of the gate—both sides, both faces. When the gate enters the seat pocket, it compresses the seat material on the upstream face and the downstream face simultaneously. The U-shape geometry creates seal contact regardless of which side the pressure comes from. This is different from two separate flat seats stacked on opposite sides of the gate. Two flat seats can gap under thermal cycling or uneven wear. The U-shape maintains continuous contact around the gate perimeter, which gives more consistent sealing performance over the valve's service life. Pneumatic Actuation—Fast, Repeatable, Automated The pneumatic cylinder actuator drives the gate through its full stroke in seconds. Single-acting spring-return cylinders use air pressure to open the valve and a mechanical spring to close it—fail-safe closure on air loss, which is the default choice for isolation duties. Double-acting cylinders use air pressure for both open and close—faster cycling, more force available for seating, but no fail-safe position without external logic. Stroke timing is repeatable. Every cycle takes the same time, applies the same seating force, and returns the same result. That consistency matters on automated process lines where the control system schedules valve operations based on fixed timing. Handwheel operation can't deliver that repeatability—human speed varies, human force varies, and the result varies with it. Elastomer Or Metal Seats—Pick Based On The Media EPDM seats for water and dilute chemicals. NBR for oils and hydrocarbon traces. Viton for aggressive solvents and higher temperatures. Metal seats with Stellite overlay for steam, high-temperature hydrocarbon, or services where elastomers degrade. The dual-seat arrangement works with any of these—the geometry is the same, the material changes. FAQ A: Yes, on elastomer seat configurations. The U-shape seat pocket creates compressive seal contact on both faces of the gate. Metal seat configurations provide near-zero leakage—acceptable for most process isolation standards, but not technically "zero" as elastomer seats can achieve. A: Spring-return (single-acting) if you need fail-safe closure—valve shuts on air supply loss. This is the standard choice for isolation duties. Double-acting if you need fast cycling in both directions and your control system handles fail-safe logic externally. A: Yes. The dual-seat arrangement requires more machining, more seat material, and a body with additional internal geometry. The cost difference is typically 15-25% over a comparable unidirectional knife gate. That premium buys you reverse-flow isolation capability that the unidirectional design simply cannot provide. A: Standard pneumatic knife gate actuators operate on 4-7 bar (60-100 psi) supply pressure. Specify your available plant air pressure when ordering—the actuator sizing depends on supply pressure to generate adequate seating force. A: No. The body cavity geometry, seat pocket design, and gate profile are different between unidirectional and bidirectional configurations. It's not a seat swap—it's a different valve architecture.
whole unit is slurry valve
Quick Specs 2" - 36" (DN50 - DN900) Class 150 - 300 (up to 20-50 bar) Manufacturer-specific, ASME B16.34 body rating A216 WCB, ductile iron (A536 65-45-12), A351 CF8M Metal-to-metal (Stellite 6 overlay), or replaceable elastomer seat insert One-piece cast body (no bolted body split), full-port bore, integrated seat pocket, heavy wall construction, gate with guiding ribs, OS&Y or pneumatic actuated One Body, No Body Gasket — That's the Whole Idea Most slurry valves come in two pieces. Two halves bolted together. A gasket sandwiched between them. That gasket sits right in the wetted zone — abrasive slurry flows over it, under it, through every microscopic gap that opens up after a thousand thermal cycles. The joint leaks. It always leaks eventually. Mines tell us the same story: they tighten the body bolts, replace the gasket, six months later it's leaking again because the slurry has been eating the gasket edge from inside the flow path. A whole unit slurry valve doesn't have that joint. The body is a single casting — one piece, no split, no body gasket, no body bolts to maintain. You still have the bonnet-to-body connection, but that gasket sits above the wetted zone where slurry never touches it. The leak path that causes the most trouble on two-piece valves simply doesn't exist here. That's the reason mines running 24/7 tailings lines specify whole unit valves. Fewer leak paths mean fewer shutdowns. In abrasive service, every joint is a liability. Remove the joint, remove the liability. What You Give Up — and Why It's Worth It A one-piece body means you can't split the valve open to inspect internals from the side. You go through the bonnet opening — remove the bonnet, pull the gate and seat up from the top. For most maintenance crews that's actually faster than unbolting a two-piece body, realigning it, and re-gasketing it. But if you need visual access to the body cavity without pulling the bonnet assembly, a two-piece design gives you that option. The tradeoff is straightforward. You lose side-access inspection. You gain zero body-joint leaks. In continuous slurry service where shutdowns cost production hours, that tradeoff favors the whole unit valve almost every time. The Gate and Seat Work Together The gate runs on guiding ribs cast into the body — not loose guides that can shift under pressure. Full-port bore means no flow restriction when the valve is open, which keeps slurry velocity smooth and reduces turbulence-induced wear on the body walls. The seat pocket is integrated into the casting, so there's no separate seat ring gap for slurry to infiltrate. For metal-to-metal seating, Stellite 6 overlay on the seat face handles abrasive wear. For applications where tighter shutoff matters more than maximum wear resistance — lower-pressure water-slurry mixtures, for example — a replaceable elastomer seat insert gives you bubble-tight closure and the option to swap the seat without replacing the entire seating surface. Heavy Walls Because Slurry Doesn't Care About Your Schedule Abrasive slurry erodes everything it touches. A thin-wall body might meet the pressure rating on paper, but after two years of tailings flowing through it at 3-4 m/s, the internal surfaces are worn thin in exactly the spots where the flow turns or accelerates. Whole unit valves are cast with heavy walls — extra thickness where experience shows wear concentrates. That's not over-engineering. That's mining experience built into the casting. FAQ A: Yes. Remove the bonnet, pull the gate, and access the seat pocket from the top. The seat insert or overlay is serviced through the bonnet opening — no need to unbolt the valve from the pipeline. A: You can, and many plants do. But in abrasive slurry service, the body gasket sits in the flow path and gets attacked from inside the line. Re-gasketing a two-piece body means a full shutdown, unbolting, realigning, and reassembling. A whole unit valve eliminates that leak path entirely. A: Up to 36" (DN900). Beyond that, casting a one-piece body becomes impractical — wall thickness, weight, and foundry capability push you toward a two-piece design at larger sizes. A: The casting is more expensive because it's larger and heavier as a single piece. But you eliminate the body gasket, body bolts, and the maintenance labor associated with that joint. Over the valve's service life, the total cost is typically lower in abrasive slurry applications. A: No. The bonnet-to-body gasket sits above the wetted zone — slurry doesn't flow across it. It's a standard pressure gasket in a clean, dry connection. Nothing like the body gasket on a two-piece valve that sits directly in the slurry flow path.
High Pressure Slurry Valve
Quick Specs 2" - 24" (DN50 - DN600) Class 300 - 900 (up to 100-150 bar depending on size) ASME B16.34, manufacturer-specific high-pressure slurry design A216 WCB, A217 WC6/WC9, A182 F316, A182 F51/F53 Metal-to-metal (Stellite 6 overlay on both seat and gate tip), reinforced elastomer inserts available for lower-pressure configurations within the range Heavy-wall one-piece or two-piece bolted body, pressure seal bonnet above Class 600, full-port bore with abrasion-resistant internal geometry, rising stem OS&Y or pneumatic/hydraulic actuated When Your Slurry Line Runs at 100 Bar Standard slurry valves stop at Class 150 or 300. That covers most tailings transport, most mineral processing circuits, most applications where "slurry valve" means something that handles abrasive media at moderate pressure. But some lines run harder. Mineral processing high-pressure pump discharge lines push 50-100 bar. Dense media separation circuits operate at pressures where a standard slurry valve body wall would be too thin — not just for the pressure rating, but for the combined attack of pressure and abrasion. At those pressures, slurry velocity through the seat area accelerates. The same abrasive particles that wear out a Class 150 seat in a year will cut through an unprotected metal seat in weeks at Class 900 flow velocities. This is why high pressure slurry valves get Stellite 6 overlay on both the seat face and the gate tip — two surfaces that see the highest velocity and the most direct particle impact. Stellite 6 is hard. It resists erosion at velocities that would strip soft metal in a single shift. The Body Is Built for Two Enemies at Once Pressure and abrasion attack different parts of the valve. Pressure stresses the body walls, the bonnet connection, every bolt and every gasket. Abrasion attacks the internal flow surfaces — the seat area, the gate edges, the body cavity walls where slurry recirculates. A high pressure slurry valve has to fight both at the same time, and that means substantially heavier wall thickness than a standard slurry valve at the same nominal size. You can see the difference if you stand a 6" Class 900 slurry valve next to a 6" Class 150 slurry valve. The Class 900 body is visibly thicker, visibly heavier. The internal geometry — flow passages, seat pocket, gate channel — is designed to minimize turbulence zones where abrasive particles accelerate and concentrate. Smooth transitions, generous radii, no sharp internal corners where slurry can stall and erode. Pressure Seal Bonnet Above Class 600 Bolted bonnets with gaskets work fine up to Class 600. Above that, the bonnet gasket becomes a liability — internal pressure pushes against it constantly, and under slurry service conditions the gasket degrades faster than in clean fluid applications. Pressure seal bonnets solve this by using internal pressure to energize the seal. As line pressure increases, the seal gets tighter. There's no bonnet gasket to replace, no bolt tension to maintain against creep. The higher the pressure, the better the bonnet seal. For Class 300-600 applications within the high-pressure range, bolted bonnets remain standard — simpler to maintain, well-proven, and the gasket loads are manageable. But if you're running Class 900 slurry, you want a pressure seal bonnet. It's not a premium option — it's the correct engineering choice. Material Selection Matches the Service A216 WCB covers most applications — carbon steel, cost-effective, proven in mining slurry at elevated pressures. A217 WC6/WC9 for higher temperature service. A182 F316 for corrosive slurry chemistry — acidic process water, chloride-rich tailings. A182 F51/F53 duplex stainless for applications where you need both corrosion resistance and mechanical strength at pressure. The material choice depends on what's in your slurry and what temperature it runs at, not just the pressure class. FAQ A: You can — for about three months. Standard gate valves aren't designed for abrasive media. The seating surfaces, body internals, and stem packing degrade rapidly when slurry flows through them. A high pressure slurry valve has Stellite overlay seats, abrasion-resistant internal geometry, and packing designed for particulate-laden fluid. The pressure rating is similar, but the slurry capability is fundamentally different. A: Reinforced elastomer inserts can handle Class 300-400 in some configurations, but above Class 600 the pressure and velocity are too high for elastomer to maintain seal integrity against abrasive slurry. Metal-to-metal with Stellite overlay is the standard seat above Class 600. A: You can, but it's not necessary and adds cost. Bolted bonnet gaskets are manageable at Class 300. Pressure seal bonnets become the recommended — and in many cases required — option above Class 600 where bolted gasket loads become impractical to maintain. A: 2" through 12" are the most common. Above 12" at Class 900, the body weight, wall thickness, and actuation force requirements become very large. 16" and 24" Class 900 slurry valves exist but are special-order items with long lead times. A: Yes — and for Class 600 and above, hydraulic actuation is often the practical choice. The seating forces required at high pressure exceed what pneumatic cylinders can deliver economically. Hydraulic actuators provide controlled, high-force operation without the air consumption issues of large pneumatic cylinders.
High Pressure Bidirectional Sealing Knife Gate Valve
Quick Specs 2" - 24" (DN50 - DN600) Class 300 - 900 (up to 150 bar / 2200 psi) ASME B16.34, manufacturer-specific bidirectional high-pressure design A216 WCB, A182 F316, A182 F51/F53, A217 WC6/WC9 Dual metal-to-metal seats (Stellite 6 overlay on upstream and downstream seats), spring-loaded or wedge-activated seat mechanism Two-piece bolted or one-piece body, heavy-wall construction, dual independent sealing boundaries (upstream seat + downstream seat), pressure seal bonnet above Class 600, OS&Y rising stem or pneumatic/hydraulic actuated Two Problems That Usually Need Two Different Valves Bidirectional sealing and high pressure rating don't normally live in the same valve. Bidirectional knife gates — the kind that seal in both flow directions — typically max out at Class 150 or 300. The elastomer seats that make bidirectional sealing affordable and practical can't handle high pressure. They deform, they extrude, they fail. High pressure knife gates exist, but most are unidirectional — the gate seals against one seat, and that seat only works when line pressure pushes the gate in the right direction. But some process lines need both. Mineral processing circuits where the flow direction reverses during batch operations. Transfer lines that can have pressure on either side depending on which pump is running. Isolation points where you need the valve to hold tight regardless of which direction pressure comes from — and that pressure is 50 bar, 100 bar, 150 bar. That's where a high pressure bidirectional knife gate valve becomes the only practical answer. Two Independent Seats, No Shared Weak Point The valve has two metal seats — upstream and downstream — both with Stellite 6 overlay. Each seat seals independently. When pressure comes from upstream, the downstream seat holds. When pressure reverses, the upstream seat holds. The gate doesn't care which direction pressure pushes because both seats are spring-loaded or wedge-activated to maintain contact pressure on the gate regardless of line pressure direction. That's the key mechanism. Spring-loaded seats press against the gate face at all times — not just when line pressure assists the seal. Line pressure reinforces the active seat, but the inactive seat still holds because its spring force keeps it engaged. Wedge-activated seats use a mechanical wedge that drives the seat against the gate when the gate reaches the closed position. Either way, both sealing boundaries are independent. If one seat is damaged, the other still seals. That's redundancy you don't get with a single-seat design. Metal Seats Because Elastomer Can't Do This Job At Class 900 pressures, elastomer seats are out. The pressure differential across the seat is too high — elastomer extrudes through the seat gap under that load, even with anti-extrusion rings. Stellite 6 overlay on both seats provides the hardness needed to resist abrasive slurry at high velocity and the metal-to-metal sealing capability needed to hold pressure at 150 bar. The seat surfaces are machined to tight tolerances and lapped for contact accuracy. It's not cheap, but it's what works. For Class 300-500 configurations within the range, reinforced elastomer inserts can be specified on one or both seats if the slurry chemistry and pressure allow it. But the standard design at Class 600 and above is dual metal-to-metal. No compromise. Heavy Body, Pressure Seal Bonnet, Serious Construction The body wall thickness follows ASME B16.34 for the rated pressure class, plus additional thickness for abrasive slurry wear allowance. At Class 900, the body is substantially heavier than a Class 300 bidirectional knife gate at the same size — that's not optional, it's structural. Pressure seal bonnet above Class 600 eliminates the bonnet gasket as a leak path under extreme internal pressure. For Class 300-600, a bolted bonnet is standard. The actuation choice matters at these pressures. OS&Y rising stem gives you visual position indication and manual operation with controlled seating force. Pneumatic actuation works for Class 300-500 where seating forces are manageable. Hydraulic actuation is recommended for Class 600 and above — the forces required to seat the gate against two spring-loaded metal seats at 150 bar exceed what pneumatic cylinders deliver efficiently. FAQ A: You can, but you're paying for bidirectional capability you don't need. If flow direction is always known, a unidirectional high pressure knife gate is simpler and less expensive. The bidirectional design is for lines where pressure can come from either side. A: The springs maintain constant contact pressure between the seat face and the gate. When line pressure is zero, the springs hold the seal. When line pressure increases, it reinforces the active seat. The inactive seat stays engaged because its spring force hasn't changed. You get a seal at zero pressure and a seal at rated pressure. A: The other seat continues to seal independently. The damaged seat may leak, but the valve still holds pressure on the intact sealing boundary. That's the redundancy advantage of dual independent seats — you don't lose the entire sealing function if one seat surface is compromised. A: Stellite 6 is the proven balance for slurry service. It's hard enough to resist abrasive wear at high velocity, it can be machined and lapped to sealing tolerances, and it welds reliably to the base metal. Tungsten carbide overlays are harder but more brittle, more difficult to machine to seal-contact tolerances, and more prone to cracking under thermal cycling in mining process lines. A: Yes — two seats means two seating surfaces to inspect and service. But the maintenance procedures are straightforward: remove the bonnet, pull the gate, inspect both seat overlays, re-lap or replace as needed. The pressure seal bonnet on Class 600+ designs actually simplifies bonnet maintenance compared to a bolted bonnet at the same pressure class.
Unidirectional Sealing Knife Gate Valve
Quick Specs 2" - 24" (DN50 - DN600) Class 150 - 300 (up to 20 bar / 300 psi) MSS SP-81, ASME B16.34 A216 WCB, A351 CF8M, A351 CF8, ductile iron Single downstream seat (elastomer: EPDM/NBR/Viton, or PTFE), gate pushes against seat in one direction only Wafer or flanged body, bonnetless or bolted bonnet, single-seat pocket on downstream side, lightweight gate, manual lever or pneumatic actuated One Seat, One Direction — and That's Enough A unidirectional knife gate valve seals in one direction. Line pressure pushes the gate against the downstream seat, the seat compresses slightly, the valve holds tight. That's the entire sealing mechanism — no springs, no dual seats, no complex internal geometry. The simplicity is the point. Reverse the flow direction and the gate lifts off the seat. The valve leaks. That sounds like a flaw, but it's not. It's the design intent. Unidirectional knife gates are specified for lines where flow direction is always known and always consistent. Gravity-fed discharge lines flowing downhill. Pump discharge lines where you isolate downstream, never upstream. Tank outlets where fluid leaves the tank and never comes back in through the same valve. If your process line has pressure on one side and the valve only needs to hold in that direction, a unidirectional knife gate does the job with fewer components, lighter construction, and 20-30% less cost than a bidirectional equivalent at the same size. Where It Works — and Where It Doesn't Mining operations use unidirectional knife gates on tailings discharge lines, process water distribution headers, and slurry transfer lines where the pump always runs in one direction. Water treatment plants use them on settled sludge draw-off lines and filter feed lines. Pulp and paper mills use them on stock flow lines where gravity and pump direction are consistent. The common thread: the line pressure always comes from one side, and isolation is only needed in that direction. Where it doesn't work: any line where pressure can reverse. Closed-loop circulating systems. Lines connected to two sources that alternate. Isolation points where you need the valve to hold regardless of which side has pressure. In those applications, a bidirectional knife gate is the correct choice — you need two seats, and you need to pay for them. Elastomer Seats That Actually Work At Class 150-300, elastomer seats are the right choice for most slurry applications. EPDM for water-based slurries and neutral pH process water. NBR for oil-laden slurries and hydrocarbon-contaminated process streams. Viton for aggressive chemical slurries with acids, solvents, or high-temperature organic media. PTFE for chemical resistance where elastomer compatibility is limited. The seat sits in a pocket on the downstream side of the body — the gate pushes into it under line pressure, the elastomer compresses around the gate edge, and you get bubble-tight shutoff at a fraction of the cost of a metal seat. The seat geometry is straightforward. Single pocket, single seat ring, single sealing direction. No upstream seat to maintain, no dual-seat alignment to manage during assembly. Replacement is simple — pull the old seat insert, push the new one into the pocket, no special tools or lapping required. Light Body, Simple Installation Wafer body design means the valve sits between flanges — no valve flanges of its own, lighter overall weight, shorter face-to-face dimension. Flanged body design gives you the valve's own flanges if the installation requires it. Either way, the body is lighter than a bidirectional knife gate at the same size because there's only one seat pocket and no internal dual-sealing mechanism. The gate is lighter too — no thick cross-section needed to engage two seats simultaneously. Manual lever operation works for 2" through 6" valves where the seating force from line pressure is sufficient and the lever gives clear visual position indication. Pneumatic actuation for larger sizes or automated process control. The actuator choice is simple because the seating force requirement is lower — line pressure does most of the work pushing the gate against the seat. FAQ A: The valve won't seal. The gate lifts off the seat under reverse pressure and the line leaks through. Arrow markings on the body show the correct flow direction. Check the arrow before installation — it's the most important marking on the valve. A: Knife gate valves are designed for slurry and particulate-laden fluids. The gate edge cuts through solids in the line — that's the "knife" function. For clean water, a standard gate valve or ball valve is more appropriate and usually less expensive. Using a knife gate on clean service is over-specification. A: One seat instead of two. Simpler body geometry. Lighter gate. Fewer internal components. The manufacturing cost is lower because the design is simpler, and the cost difference is 20-30% at common sizes. You pay for bidirectional capability only when you need it. A: It depends on the slurry composition, velocity, and operating frequency. In typical mining tailings service at 2-3 m/s, EPDM or NBR seats last 12-18 months. Replacement takes minutes — pull the worn insert, push in a new one. The seat is a consumable component, and that's the correct way to think about it. A: Bonnetless designs work well for smaller sizes (2"-8") in moderate-duty applications where the gate stays inside the body cavity and doesn't need a full bonnet enclosure. For larger sizes or continuous heavy-duty service, a bolted bonnet protects the stem and packing from slurry exposure and is the more robust choice.
Technical Overview
Knife gate valves cut through media that regular gate valves can't handle—fibrous pulp, settling slurries, tailings with suspended solids, sticky process residues that jam a parallel-seat gate before it reaches closed position. The blade-shaped gate slices through whatever sits in the flow path instead of trying to push it aside. That's the fundamental difference between a knife gate and a conventional wedge gate: one cuts, one wedges, and in media that accumulates on the seat surface, cutting wins. FLOWKS manufactures nine knife gate and slurry valve configurations—from lightweight wafer unidirectional isolation valves through heavy-duty long-pattern slurry valves, bidirectional dual-seat designs, polyurethane-lined abrasive service valves, and high-pressure units rated to Class 900. Wafer bodies fit between pipeline flanges with minimal footprint. Flanged bodies bolt directly into the line. One-piece ("whole unit") castings eliminate the body split gasket as a leak path. Bidirectional designs seat the gate from both directions with two independent sealing boundaries. Unidirectional designs seat in one direction only—cheaper, simpler, adequate for lines with known flow direction. Polyurethane lining shields every wetted surface from abrasive attack. High-pressure configurations use Stellite 6 metal seats and pressure seal bonnets for service beyond 50 bar. Every configuration shares the same operating principle: a sharp-edged gate that cuts through the media and seats against a peripheral seal, rather than wedging between two parallel faces that trap debris.
FLOWKS knife gate valves and slurry valves provide reliable shutoff in media conditions that defeat conventional gate valves—pulp stock, mining slurries, tailings transport, wastewater with suspended solids, and sticky process residues. The blade-shaped gate slices through accumulated media rather than wedging it aside, preventing seat cavity blockage and ensuring full-bore shutoff even after prolonged service in settling or fibrous media. Wafer knife gate valves offer the lightest, most compact isolation option for Class 150 service—unidirectional sealing, minimal installation footprint, lowest cost per size. Bidirectional knife gate valves add dual-seat sealing for lines with pressure on both sides of the valve. High pressure knife gate valves extend service to Class 300–900 with metal seats and pressure seal bonnets. Polyurethane-lined knife gate valves protect all wetted surfaces from abrasive slurries with full-body PU liners that outlast hard rubber by 5–10x. Heavy-duty long-pattern slurry valves provide structural depth and full-port bore for demanding mining and mineral processing applications. Whole unit slurry valves use one-piece cast bodies to eliminate the body gasket leak path entirely. High pressure slurry valves combine abrasive media resistance with Class 300–900 pressure ratings and Stellite 6 metal seats. Unidirectional sealing knife gate valves deliver cost-effective single-direction isolation for lines with consistent flow direction. Manual, pneumatic, and hydraulic actuation options available across all configurations.
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Industries Using Knife Gate Valves
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Water Treatment
Reliable flow control solutions for desalination, wastewater, and potable water systems. FLOWKS butterfly valves and check valves are widely used in water infrastructure projects.
Mining
Abrasion-resistant valves for slurry, tailings, and mineral processing applications. FLOWKS knife gate valves and butterfly valves are built to withstand harsh mining environments.
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Ball Valves
FLOWKS offers floating ball valve, trunnion mounted ball valve and top entry ball valve for oil & gas, petrochemical and power generation. Designed per API 6D, API 608 and ASME B16.34.
DBB Valves
FLOWKS Double Block & Bleed (DBB) valves provide dual isolation with bleed verification in a single compact body. Replacing traditional multi-valve installations, FLOWKS DBB valves reduce weight, space and potential leak paths. Available in bolted bonnet, all-welded and expanding gate designs per API 6D and API 607.
Gate Valves
FLOWKS gate valves for isolation service in piping systems. Flexible wedge, solid wedge, slab and expanding gate designs per API 600, API 602 and ASME B16.34.
Globe Valves
FLOWKS globe valves for throttling and isolation. Standard, angle, Y-pattern and bellows seal configurations per API 602 and BS 1868.