Knife gate valve

Product Overview

The Bonneted Knife Gate Valve is a knife‑edge gate valve with an enclosed bonnet construction. It is designed only for ON‑OFF (open/close) service – not for flow regulation. Unlike conventional open‑frame knife gate valves (which have no bonnet and expose the top of the gate), this product features a bolted, closed bonnet that fully encloses the packing box and stem, effectively preventing media leakage and allowing higher pipeline pressure ratings.

This valve is suitable for hazardous, volatile, toxic, or odorous media, as well as applications where strict leakage control is required. The sharp knife‑edge gate cuts through fibers, particles, and other materials during closure, preventing clogging. The body flow path has no recesses to avoid material buildup. The valve has flanged connections, with nominal diameters from DN50 to DN600, pressure ratings PN10/PN16 (Class 150), and body materials including cast iron, carbon steel, and stainless steel. Actuators can be manual, electric, or pneumatic.

Product Structure

The Bonneted Knife Gate Valve mainly consists of the actuator (ON‑OFF type) and the enclosed valve body assembly.

Actuator (ON‑OFF Type):

1. Available in manual (handwheel), electric, or pneumatic.

2. Electric actuator: motor, gearbox, travel limit switches, torque protection, handwheel.

3. Pneumatic actuator: cylinder, solenoid valve, limit switches.

4. All actuators are ON‑OFF type – not for modulation.

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Enclosed Valve Body Assembly:

1. Body: Cast or fabricated body in gray cast iron, ductile iron, carbon steel (WCB), stainless steel (CF8/CF8M), etc. Flanged ends conforming to GB/T 9113, ANSI B16.5, EN 1092‑1, etc. Full‑bore flow path with no recesses.

2. Gate: Stainless steel (304, 316, 310S) knife‑edge gate with a sharp edge to cut through fibers and particles. The gate surface can be hardfaced with Stellite or chrome‑plated.

3. Seats: Available in rubber (EPDM, NBR, FKM), PTFE, or metal sealing; bidirectional sealing optional.

4. Stem: Stainless steel trapezoidal‑thread stem, moving the gate up and down.

5. Enclosed Bonnet: Bolted to the top of the body, fully covering the packing box and stem. A gasket (spiral wound stainless steel + graphite or metal ring) is used between the bonnet and body to ensure no external leakage. The bonnet houses the packing box, which contains PTFE or flexible graphite packing compressed by a packing gland.

6. Yoke: Connects the bonnet to the actuator.

Compared with open‑frame knife gate valves, the bonneted version fully encloses the stem and packing, preventing media escape from the top and providing higher safety.

Function

1. Enclosed Leak‑Tight Design: The bonnet is bolted to the body, and the packing box is fully enclosed, effectively preventing leakage of hazardous, volatile, or toxic media, protecting operators and the environment.

2. Higher Pressure Capability: The enclosed construction increases overall valve strength, allowing higher pipeline pressure ratings (up to PN16 or higher) compared with open‑frame knife gate valves.

3. Knife‑Edge Cutting Function: The sharp edge of the gate cuts through hanging fibers, paper, plastic strips, and other materials during closure, preventing clogging.

4. Self‑Cleaning Flow Path: The body flow path has no recesses. When fully open, the media can flush the interior, preventing solids accumulation.

5. Bidirectional Sealing (optional): A bidirectional floating seat or double‑sided sealing design allows the valve to withstand media pressure from either direction.

6. Full‑Bore Low Flow Resistance: When fully open, the gate is completely out of the flow path, providing minimal pressure loss.

7. Remote ON‑OFF Control: With electric or pneumatic actuators, remote automatic open/close operation is possible.

8. Manual Emergency Operation: Electric/pneumatic actuators are equipped with a handwheel for manual operation during power or air supply failure.

Working Conditions

1. Applicable Media: Sewage, sludge, slurry, coal slurry, pulp, chemical slurries, oily sludge, hazardous liquids, volatile solvents, toxic media, etc.

2. Temperature Range: –20°C to +200°C (PTFE seats); –20°C to +80°C (rubber seats); –29°C to +550°C (metal seats).

3. Pressure Rating: PN10, PN16 (Class 150); higher ratings available on request.

4. Nominal Diameter: DN50 – DN600 (2″ – 24″); larger sizes available on request.

5. Installation Orientation: Vertical stem‑up recommended.

6. Typical Applications:

   1. Odor control in wastewater treatment plants (enclosed bonnet prevents gas escape)

   2. Shut‑off of toxic media lines in chemical plants

   3. Oily sludge and oily wastewater pipelines

   4. Solvent lines in pharmaceutical plants

   5. Landfill leachate treatment systems

   6. Pulp lines in paper mills (with leakage prevention requirement)

   7. Underground mine drainage systems (high safety requirement)

Summary

The Bonneted Knife Gate Valve, with its advantages of enclosed bonnet construction, leak‑tight design, knife‑edge cutting function, and self‑cleaning flow path, is the ideal shut‑off valve for handling hazardous, volatile, toxic, or odorous media. Compared with conventional open‑frame knife gate valves, the bonneted version effectively prevents media escape through the stem, protecting personnel and the environment, while also allowing higher pipeline pressure ratings.

This valve is designed for fully open or fully closed operation only – not for flow regulation. With flanged connections, a full‑bore flow path, and optional manual or automated actuators, the Bonneted Knife Gate Valve is a reliable and safe choice for automated ON‑OFF pipeline systems that require strict leakage prevention and handle hazardous media containing solid particles or fibers.