What Is a Bonneted Knife Gate Valve?

A bonneted knife gate valve is a specialized type of knife gate valve that includes a bonnet — a solid enclosure on top of the valve body that seals the stem area. This design provides enhanced sealing performance, protecting internal components from external contaminants such as dust, moisture, and aggressive media.

In contrast to standard (bonnetless) knife gate valves, which have an open-yoke design, bonneted versions offer a fully enclosed structure, making them more suitable for demanding or hazardous environments.

How Does It Work?

Like all knife gate valves, a bonneted model uses a thin blade-like gate that slides vertically into the flow stream to cut through media and isolate flow. The key difference lies in the bonnet enclosure:

• The bonnet covers the rising stem and gland packing, shielding them from media exposure.

• This enclosed design helps maintain tight sealing, reduce leakage, and extend service life — especially in high-pressure, high-temperature, or toxic fluid applications.

Key Components of a Bonneted Knife Gate Valve

Benefits of Bonneted Knife Gate Valves

✅ Improved Sealing Performance
The bonnet adds an extra sealing layer, minimizing stem leakage even under high pressure or with abrasive media.

✅ Protection in Harsh Environments
Ideal for dusty, corrosive, or wet conditions, where open-yoke valves would suffer wear or failure.

✅ Longer Service Life
Reduced exposure to external elements extends the life of stem seals and packing.

✅ Better Safety
Enclosed components reduce operator exposure to toxic or hazardous fluids.

✅ Suitable for Vacuum or High-Pressure Systems
Bonneted valves can be rated for vacuum service or higher pressure classes (up to ANSI Class 150+), depending on design.

Common Applications

Bonneted knife gate valves are widely used in industries where tight shutoff, media isolation, and environmental protection are essential:

• Pulp & Paper Mills (handling slurry and fibrous pulp)

• Mining & Mineral Processing

• Power Plants (ash handling, FGD systems)

• Chemical & Petrochemical Plants

• Wastewater Treatment

• Bulk Powder or Slurry Transport Systems

• Oil & Gas Refineries

Bonneted vs. Bonnetless Knife Gate Valves

Material & Size Options

Bonneted knife gate valves are available in a variety of materials and sizes, depending on the application:

• Body Materials: Cast Iron, Ductile Iron, Stainless Steel, Alloy Steel

• Gate Materials: 304, 316 Stainless Steel, Monel, Hastelloy

• Bonnet Types: Standard bolted bonnet, pressure-sealed bonnet

• Sizes: Commonly from 2” up to 48” or larger

• Pressure Ratings: Usually up to ANSI 150, higher ratings available upon request

Actuation Options

Bonneted knife gate valves can be operated manually or with actuators:

• Manual Handwheel or Gearbox

• Electric Actuators (ideal for remote or automated control)

• Pneumatic Cylinders (for fast on/off control)

• Hydraulic Actuators (used in heavy-duty or safety-critical systems)

Conclusion

Bonneted knife gate valves are a reliable solution for industries that demand superior sealing, long-term durability, and safe operation in harsh conditions. While they may come at a higher cost compared to bonnetless designs, the added protection, performance, and longevity often justify the investment.

If your system involves abrasive slurries, hazardous chemicals, or high-pressure processes, a bonneted knife gate valve may be the best-fit choice.