Features of Electric Knife Gate Valves and How to Repair Them

Release time:

2022-02-28

What are the applications of knife gate valves? The introduction of knife gate valves has addressed the issues of heavy weight, high flow resistance, large footprint, and difficult installation associated with conventional gate valves. Knife gate valves can serve as a replacement for general globe valves and operate under working pressures ranging from 1.0 MPa to 2.5 MPa and temperatures from -29°C to 550°C. The gate plate of a knife gate valve features a shearing action that can scrape off adhesive deposits on the sealing surface, automatically removing impurities. The stainless steel gate plate effectively prevents sealing leaks caused by corrosion.

What are the applications of knife gate valves? The introduction of knife gate valves has addressed the issues of heavy weight, high flow resistance, large footprint, and difficult installation associated with conventional gate valves. Knife gate valves can serve as a replacement for general globe valves and operate under working pressures ranging from 1.0 MPa to 2.5 MPa and temperatures from -29°C to 550°C. The gate plate of a knife gate valve features a shearing action that can scrape off adhesive deposits on the sealing surface and automatically remove impurities. The stainless steel gate plate effectively prevents sealing leaks caused by corrosion.

I. Characteristics of Knife Gate Valves

1. The liftable sealing surface of the gate can scrape off adhesive from the sealing surface and automatically remove impurities.

2. Stainless steel gates can prevent sealing leaks caused by corrosion; fine grinding and polishing can achieve even better sealing performance.

3. The stainless steel valve body is durable and long-lasting. The design of reinforcing ribs on the valve body enhances its strength, while the double-headed screws allow for faster opening and closing.

4. Both the valve body and the stuffing box are cast. The valve body is integrally cast in a flanged design, and the material can be selected—304, 316, 316L, WCB, or 2Cr13—according to the user’s requirements. The sealing ring is made of PTFE-reinforced PTFE, offering excellent corrosion resistance, wear resistance, and zero residue.

5. The fully circular DC channel design ensures zero residue and no blockage.

6. The scientifically designed upper seal packing gland ensures that the upper seal is safe, effective, and durable.

7. The structure has a short length, which can save on raw materials and installation space while also effectively supporting the pipeline’s strength.

8. The triangular bracket saves raw materials while ensuring the required mechanical performance.

9. The guide blocks on the gate valve body ensure proper movement of the gate. The compression blocks guarantee an effective seal of the gate plate.

10. The valve disc has five support points. When the valve is closed and under backpressure, the valve disc will not move.

II. Maintenance of Knife Gate Valves

Each type of equipment has its own unique value in use, and valve equipment plays a crucial role across various industries. There are many different kinds of valves, such as ball valves, butterfly valves, and electric knife gate valves. Initially, China did not have electric knife gate valves; however, since then, knife gate valves have risen rapidly and have entered diverse industries within just two decades.

Previously, all electric knife-type gate valves had to be purchased from other countries, making them relatively expensive. However, domestic enterprises lacked a strong maintenance awareness; as a result, these valves often ended up damaged due to prolonged use or improper operating procedures. Moreover, since there were no qualified repair personnel available domestically, many companies simply sold these valves as scrap, leading to a significant waste of resources. In many domestic industries, the equipment could not be repaired at all, and even when repairs were possible, the results were far from ideal. This drastically shortened the service life of the equipment and posed serious safety risks. If leaks occurred without any preventive maintenance measures in place, the equipment was usually already severely damaged—making repairs much more difficult and often resulting in substantial financial losses. Later, many industries and enterprises recognized the importance of this issue and began to specially train maintenance personnel, enabling them to promptly address problems and thereby significantly reducing enterprise losses.

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?