Knife gate valve

Product Overview

The Bonnetless Knife Gate Valve is a knife‑edge gate valve with an open‑frame construction (no bonnet), exposing the top of the gate. It is designed only for ON‑OFF (open/close) service – not for flow regulation. Unlike bonneted knife gate valves, this product features a simple, open structure that is lightweight, low‑cost, and allows easy visual inspection of the gate position and cleaning of accumulated material. This valve is suitable for non‑hazardous, non‑volatile media such as sewage, pulp, slurry, and mud.

It is not recommended for toxic, volatile, or applications requiring strict leakage control. 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, and the absence of a bonnet makes the interior easier to flush. The valve has flanged connections, with nominal diameters from DN50 to DN800, 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 Bonnetless Knife Gate Valve mainly consists of the actuator (ON‑OFF type) and the open‑frame 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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Open‑Frame 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. The top of the gate is exposed and directly connected to the actuator.

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. With no bonnet, the stem connection is exposed.

5. Packing Box: Located at the top of the body, containing PTFE or flexible graphite packing, compressed by a packing gland to prevent media leakage along the stem. However, because there is no bonnet, the packing area is exposed and is not suitable for hazardous media.

6. Yoke: Connects the body to the actuator (typically mounted directly on the top of the body).

The bonnetless knife gate valve has a simple construction, lower cost, and allows easy visual access to the gate and internal cleaning.

Function

1. Open‑Frame Design: No enclosed bonnet; the top of the gate is exposed. Simple structure, light weight, low cost.

2. Easy Visual Inspection and Cleaning: The gate position and internal buildup can be directly observed, facilitating flushing and maintenance.

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, mud, fiber suspensions, particle‑laden liquids (non‑hazardous, non‑volatile).

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 – DN800 (2″ – 32″); larger sizes available on request.

5. Installation Orientation: Vertical stem‑up recommended (cannot be installed upside down because there is no bonnet).

6. Not Suitable For: Toxic media, volatile solvents, hazardous gases, or applications requiring strict leakage control.

7. Typical Applications:

   1. Sludge discharge and sewage lines in wastewater treatment plants

   2. Pulp transport in paper mills

   3. Mine tailings and concentrate slurry pipelines

   4. Ash and slag discharge in coal‑fired power plants

   5. Fruit pulp and sauce lines in the food industry

   6. Industrial wastewater treatment systems

   7. Metallurgical beneficiation slurry lines

Summary

The Bonnetless Knife Gate Valve, with its advantages of open‑frame no‑bonnet construction, knife‑edge cutting function, self‑cleaning flow path, and low cost, is an economical and practical shut‑off valve for non‑hazardous media such as sewage, pulp, and slurry. Compared with bonneted knife gate valves, the bonnetless version is simpler, lighter, and lower in cost, while allowing easy visual inspection of the gate position and cleaning of internal buildup.

However, this valve is not suitable for toxic, volatile, or applications requiring strict leakage control. With flanged connections, a full‑bore flow path, and optional manual or automated actuators, the Bonnetless Knife Gate Valve is an efficient and economical solution for automated ON‑OFF pipeline systems handling non‑hazardous, non‑volatile media containing solid particles or fibers.