Everything You Need to Know About Knife Gate Valves

August 02, 2024
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What is a Knife Gate Valve?

A knife gate valve is a type of gate valve. It has a shorter body length and a thinner gate. The opening and closing component is the gate, which moves perpendicular to the direction of the fluid flow. The bottom of the gate has a knife-like bevel that can cut through fibers in the medium, hence the name "knife gate valve." It is used for transporting slurry, coal slurry, mineral powder, dry ash, coal powder, pulp, mud, mixtures of material and water, or material and gas in both wet and dry mediums. The operating pressure is typically ≤PN10.

The main features of knife gate valves include simple structure, small size, lightweight, good sealing performance, corrosion resistance, and flexible operation. The knite gate valve catalog PDF from Union Valve can provide you with more information!

Symbol Representation of Knife Gate Valves

Classification of Knife Gate Valves

1.By Stem Type

Knife gate valves come in two forms: rising stem and non-rising stem.

Rising Stem Knife Gate Valve: The stem is of a rising type, where the stem and gate move up and down together, completing the opening and closing process of the gate valve.

Non-Rising Stem Knife Gate Valve: The nut is fixed to the gate, and the gate is raised and lowered by rotating the stem, which is of a rotating type. For installations with limited height space, non-rising stem gate valves can be considered.

2.By Body Type

Knife gate valves have two types of valve bodies: split body and integral body.

Split Body Valve: The valve body is divided into two parts, which are processed separately and then fixed together with bolts, making it easier to process and maintain.

Integral Body Valve: The integral body has high strength and less risk of external leakage.

3.By Sealing Type

The seat of a knife gate valve can use soft sealing, hard sealing, or composite sealing.

Soft Sealing: Uses non-metallic materials like rubber and PTFE, providing excellent sealing performance with zero leakage.

Hard Sealing: Involves metal-to-metal sealing, which has a certain amount of leakage.

4.By Connection Method

Knife gate valves can be classified based on their connection methods into flange type, lug type, and wafer type.

Knife Gate Valves

How Knife Gate Valves are Sealed?

一． Valve Body Sealing

The inner chamber of the valve body has a groove where an elastic sealing strip is placed. When closing, the gate moves downward, compressing the sealing strip into the groove, achieving a seal between the valve body and the gate.

When opening, the gate moves upward, and the edge of the gate bottom separates from the sealing strip, allowing the sealing strip to spring back and align with the groove. For better performance, it is recommended to use hollow rubber sealing strips.

This sealing structure between the gate and the valve body prevents sediment from accumulating in the valve body groove, enhancing the sealing performance of the knife gate valve. This structure is commonly used in slurry valves.

二．Dual Sealing with O-Ring and Metal Hard Seal

The valve seat employs a dual sealing design using a rubber O-ring and a metal hard seal. The O-ring slightly protrudes beyond the metal sealing surface. When the medium in the pipeline is at low pressure, the O-ring elastically deforms to maintain a seal with the gate. At high pressure, the gate first contacts the rubber O-ring and then the metal valve seat, creating a dual sealing effect.

This structure allows the O-ring to deform within its elastic range, enhancing its lifespan. At low pressure, the rubber O-ring contacts the gate surface, maintaining excellent sealing performance. The O-ring is also easy to replace.

What Are The Driving Methods Of Knife Gate Valves?

Knife gate valves can be actuated using manual, pneumatic, electric, hydraulic, and chain drive methods.

Manual Drive: For valve diameters (DN) ≥ 400 mm or when the nominal pressure is high, bevel gear drive should be considered to reduce the operating torque on the handwheel.

Pneumatic Knife Gate Valve: Consider the need for accessories such as solenoid valves, filter regulators, limit switches, and whether explosion-proofing is required.

Electric Knife Gate Valve: Consider the voltage of the electric actuator, control method, and explosion-proof requirements.

Hydraulic Knife Gate Valve: Determine if it is an integrated electro-hydraulic type. A single hydraulic cylinder requires a hydraulic station with supporting devices.

Chain Drive: When manual operation is inconvenient at high altitudes, chain wheel operation should be considered.

Where are knife gate valves commonly used?

Mining, Coal Washing, and Steel Industry: Used in coal washing pipelines, slag slurry pipelines, and ash discharge pipelines.
Purification Systems: Used for wastewater, sludge, waste, and clarified water containing suspended solids.
Pulp and Paper Industry: Suitable for any concentration of pulp and material-water mixtures.
Power Plant Ash Removal: Used for ash slurry.

What Are the Differences Between Knife Gate Valves and Conventional Gate Valves?

There are many types of gate valves, and knife gate valves are one of them. Knife gate valves and conventional gate valves have some differences in structure and characteristics, mainly reflected in the following aspects:

Basic Differences	Knife Gate Valve	Conventional Gate Valve
Different opening and closing parts	The component is a blade, which has a simpler structure and makes opening and closing more convenient.	The component is a gate.
Different structures	Simplified structure, consisting of a blade and a valve body, with a more compact design.	Relatively complex structure, mainly composed of a gate, valve seat, valve stem, and other components.
Applicable media	Performs excellently in handling slurry, viscous media, and fluids containing suspended solids. It has better wear and corrosion resistance.	Suitable for clean, low to medium viscosity fluids without suspended solids. It is used for general flow control in non-abrasive, non-corrosive environments.
Flow direction	Often designed for unidirectional flow.	Designed for bidirectional flow.
Cost Comparison	Usually more expensive due to specialized materials and manufacturing processes.	Generally more cost-effective compared to knife gate valves.
Weight comparison	Typically lighter due to thin design, compact valve body, and less material used.	Usually heavier due to a solid gate, sturdy valve body structure, and more material used to handle high pressure and harsh conditions.

Example Weights For a 6-inch (150 mm) valve:

Knife Gate Valve: Approximately 20-30 kilograms (depending on the material and manufacturer).

Conventional Gate Valve: Approximately 50-70 kilograms (depending on the material and manufacturer).

Compared to Conventional Gate Valves, Knife Gate Valves Offer Several Advantages:

U-Shaped Sealing Gasket:Provides excellent sealing performance.
Full-Bore Design by UNION VALVE: Ensures strong medium throughput. Additionally, it allows for easy installation, disassembly, and maintenance in environments with dirty media. The valve seals can be replaced without removing the valve, simplifying maintenance.
Gate with Knife Function: The gate effectively cuts off various debris in the medium, preventing leakage after cutting through blocky, granular, and fibrous media.
Ultra-Short Structure Length: Knife gate valves have a compact size, low flow resistance, lightweight design, save materials, and occupy minimal effective space.

Despite being approximately 20% more expensive than conventional gate valves, the superior performance of knife gate valves has gained widespread market recognition.

In Summary

Knife gate valves have broad application value in the industrial field. When choosing to use knife gate valves, it is important to weigh their advantages and disadvantages based on actual working conditions and requirements to ensure the normal operation and efficient use of the equipment.

If you are looking for a reliable Chinese knife gate valve manufacturer, Union Valve is a wise choice. Union Valve is a professional gate valve manufacturer in China, with products certified by ISO9001:2008, CE, WRAS, ACS, EAC, TUV, and SGS. They offer a wide variety of types and specifications. Based on your specific needs, they provide comprehensive services. For more information, please contact us as soon as possible.

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