5 Must-Have Features in a Knife Gate Valve

Key Features to Consider When Purchasing a Knife Gate Valve

When it comes to industrial processes, having the right equipment is crucial for the efficiency and reliability of operations. One essential component in various industries is the knife gate valve. These valves play a critical role in controlling the flow of materials, such as slurries, viscous fluids, and solids. If you're in the market for a knife gate valve, there are several key features you should consider to ensure you select the right one for your specific needs.

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Valve Design

The design of the knife gate valve is the first feature to consider. There are three common designs: uni-directional, bi-directional, and through-going. Uni-directional valves are suitable when the flow should only go in one direction, while bi-directional valves allow for flow in both directions. Through-going valves are designed for applications where the valve needs to pass through immovable solids. 

Actuation Method

The actuation method is another crucial feature to consider. Knife gate valves can be operated manually, pneumatically, or hydraulically. Manual actuation is cost-effective but requires human intervention. Pneumatic and hydraulic actuation methods are more automated and suitable for applications with high frequency or demanding conditions. Consider the level of automation and control you need when selecting the actuation method for your knife gate valve.

Body Material

The body material of the valve is vital for its durability and resistance to corrosion and wear. Common materials used for knife gate valves include cast iron, carbon steel, stainless steel, and various alloys. The choice of the body material depends on the type of fluid being controlled and the operating conditions. Consult with experts or refer to industry standards to select the appropriate material that can withstand the specific demands of your application.

Seat Material

The seat material of the knife gate valve is crucial for ensuring a tight shut-off and preventing leakage. The choice of seat material should be compatible with the fluid being handled. Common seat materials include rubber, metal, and polyurethane. Rubber seats provide excellent sealing properties, while metal seats offer increased durability. Consider the fluid characteristics and operating conditions to select the most suitable seat material for optimal performance.

Size and Pressure Rating

Another vital consideration is the valve's size and pressure rating. Determine the required pipe diameter and pressure class to ensure compatibility with your existing system. Oversized or undersized valves may lead to inefficiencies or operational issues. Additionally, consider the maximum pressure the valve will be exposed to and ensure that its pressure rating exceeds these requirements.

Maintenance and Support

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Lastly, consider the manufacturer's reputation for maintenance and support. Ensure that the valve supplier can provide timely and reliable after-sales support, including spare parts availability and technical assistance. Good customer support can minimize downtime and help resolve any issues that may arise during the valve's lifespan.

Selecting the right knife gate valve is crucial for optimal performance and efficiency in industrial processes. By considering important features such as valve design, actuation method, body and seat materials, size and pressure rating, and maintenance and support, you can make an informed decision. 

Knife gate valve valve stem failure

Knife gate valve valve stem failure is mostly caused by excessive operation, resulting in damage to the valve stem thread or bending of the valve stem, or due to the imbalance of the valve stem and nut, nut misalignment, thread corrosion, rust, etc. In addition, the selection of materials can also cause valve stem failure, such as the valve stem and valve stem nut being made of the same material, which is easily stuck and causes failure.

Solution: When using a knife gate valve, workers should operate it carefully, strictly control the opening and closing dimensions, and avoid strong switching to prevent bending of the valve stem. Do not fully open the valve to the upper end point, but open it to a suitable degree and then reverse the handwheel by one turn to ensure the tight sealing of the upper side of the thread and prevent medium-induced upward impact on the valve stem. Adjust the position of the nut. If corrosion and rust cannot be prevented, replace the valve stem and nut in time. Choose nuts and valve stems made of different materials.

Knife gate valve stem rolling insensitivity or jamming

The main reasons for the insensitivity or jamming of the knife gate valve stem are excessive packing compression, improper filling of the packing into the packing box, improper clearance between the valve stem and the bushing, valve stem bending, rough surface finish of the thread, inappropriate selection of materials for the valve stem and bushing, etc.

Solution: Loosen the packing gland screws appropriately; increase the filling according to the specifications; control the clearance between the valve stem and the bushing within the specifications; control the roughness of the thread's surface finish within the specifications.

Knife gate valve bonnet gland hole leakage

Some valve bonnets have gland holes for factory pressure tests, which may cause water leakage during use. The main reason is that the gland hole is not properly tightened.

Solution: Tighten it again, or remove the bolt from the gland hole, take out the copper gasket inside, and then clean the screw hole and screw the bolt back in and weld it with electric welding.

Knife gate valve body and bonnet joint leakage

The insufficient or uneven tightening of the bolts at the flange joint causes the flange to tilt, resulting in leakage at the joint between the knife gate valve body and bonnet. Or there is damage to the joint surface between the valve body and bonnet, and the flange gasket is damaged, etc., which causes leakage at the joint.

Solution: The flange should be tightened diagonally; pay attention to maintaining the joint surface during use; choose better quality gaskets. If the contact surface cannot be adjusted due to quality issues, reprocessing can be done on the contact surface.

Knife gate valve packing box leakage

The leakage of the packing box of the knife gate valve is caused by the incompatibility between the packing and the working medium in terms of corrosion, temperature, and pressure, incorrect filling method, poor surface finish of the valve stem, corrosion, rust, or the aging of the packing due to prolonged use.

Solution: Choose the correct packing method; fill the packing according to the correct method; choose a valve stem with the required surface finish; adopt appropriate protective measures to prevent corrosion, and replace it in time if rust is found.