What are the criteria for selecting knife gate valves?

Release time:

2022-07-26

A knife gate valve is a type of gate valve assembly consisting of an electric actuator and a ball valve. It is a pipeline pressure component used in industrial automation process control, typically employed for remote on-off (switching) control of pipeline media. So, what are the criteria for selecting a knife gate valve?

　　 Knife Gate Valve It is a gate valve device composed of an electric actuator and a ball valve. It is a pipeline pressure component used for process control in industrial automation, typically employed for remote on-off (switching) control of pipeline media. So, what are the criteria for selecting knife-type gate valves?

Knife Gate Valve

　　1. Knife Gate Valve It is a type of control component widely used in fluid pipeline systems. It has a wide range of applications and demonstrates excellent performance in controlling flow rate, pressure, and backflow. Since the quality of knife gate valves significantly impacts the safety of pipelines, it is essential to follow specific steps and criteria when selecting such valves.

　　2. Clearly identify the diameter of your company’s pipeline and understand the required diameter and connection method for knife gate valves. Based on the pipeline’s needs, first determine several common parameters of the knife gate valve, such as flow capacity, allowable flow resistance, and valve seat hole size. If these parameters are selected incorrectly, the knife gate valve’s effectiveness in flow control will be significantly reduced.

　　3. Select the appropriate material based on the operating temperature of the pipeline; of course, you should also take into account the working pressure of the pipeline. In addition, we’d like to remind everyone not to rush into selecting a product. First, we should understand what the popular knife gate valve products are and what their performance characteristics are. A better way to gain this understanding is to contact several knife gate valve manufacturers and ask them to provide product catalogs and samples. Only by comparing three different suppliers can we choose a product that offers the best value for money.

　　Internal leakage in knife gate valves generally refers to the phenomenon where, even after the valve is fully closed, medium still flows out, leaks, or drips from the circulation diameter outlet. In general, this indicates that the seal is not tight and the sealing performance is poor. The cause of this failure is usually due to erosion and wear caused by the medium, or the presence of impurities. Even if the screw (stem) of the knife gate valve is fully tightened, medium can still flow through because there remains a gap between the valve core and the valve body.

　　External leakage in knife gate valves generally refers to the leakage of medium from the external seals of the valve’s packing after the electric actuator has fully closed or opened the valve. Specifically, this can occur due to loosening of the seal between the electric actuator and the connecting threads, resulting in medium escaping through the sealing surface at the connection; or due to leakage between the valve stem and the gland (i.e., the gland located at the base of the pressure plate on the valve stem); or due to external leakage caused by sand holes in the valve body blank; or even due to external leakage resulting from wear of the valve body caused by medium erosion.

　　Impact Knife Gate Valve The primary factors contributing to the deadband include friction, stroke, valve shaft torsion, and amplifier deadband. Different control valves exhibit varying sensitivities to friction. For example, rotary valves are highly sensitive to friction caused by high seat loads; therefore, this aspect should be carefully considered during operation. However, for certain seals, a higher seat load is required to ensure proper closure. Yet, if such valves are poorly designed, they tend to develop a larger deadband, which can significantly and decisively affect process variability.

The vast majority of stainless steel knife gate valves employ forced sealing: that is, when the valve is closed, an external force is applied to forcibly press the gate against the high-pressure valve seat, thereby ensuring a tight seal on the sealing surfaces. Some gates can also be designed to undergo slight deformation, which helps improve their manufacturability and compensate for any misalignment in the sealing surface angles that may occur during the manufacturing process. Such gates are referred to as flexible gates. The majority of knife gate valves rely on forced sealing—meaning that when the valve is closed, an external force is used to press the gate firmly against the high-pressure valve seat, thus guaranteeing a secure seal on the sealing surfaces. Valves of this type are generally installed horizontally in pipelines.

2023-05-11

Next, let’s talk about several operating procedures for knife gate valves.

When a gate valve is closed, the sealing surfaces rely solely on the pressure of the medium to achieve a seal—specifically, the sealing surface of the gate is pressed against the valve seat on the opposite side by the medium’s pressure, thereby ensuring a tight seal. This type of sealing is known as self-sealing. In contrast, most gate valves employ forced sealing: when the valve is closed, an external force must be applied to press the gate against the valve seat in order to guarantee the sealing performance of the sealing surfaces. Such valves should be installed vertically in the pipeline.

2023-05-11

Next, let’s talk about whether knife gate valves have fire-resistant and anti-static requirements.

When an electrostatic knife gate valve is opened or closed, the sphere and the valve seat experience mutual friction. The static electricity generated by this friction tends to accumulate on the sphere—something that is unacceptable for ball valves used in gas, fuel, and chemical pipelines, as it could potentially lead to pipeline explosions. Ball valves with antistatic designs are equipped with static discharge devices.

2023-05-11

Next, let’s talk about some important considerations for the installation, operation, and maintenance of pneumatic knife gate valves.

Pneumatic knife gate valves have a wide range of applications, spanning from ordinary fields to more diverse industries—from coal preparation, gangue removal, and slag discharge in coal-fired power plants to urban wastewater treatment; from general industrial pipelines to pipeline systems used in food, sanitation, and pharmaceutical industries. So, what are the key considerations when installing, using, and maintaining pneumatic knife gate valves?

2023-05-11

Slurry Valve Manufacturer: How are stainless steel knife gate valves good?