How Does the Gate Valve Work?

In industrial pipeline systems, gate valves, as one of the most commonly used shut-off valves, are widely used in various engineering projects such as petroleum, chemical, power, metallurgy, etc. due to their advantages of simple structure, low flow resistance, and good sealing performance. Whether it is a new pipeline or a renovation project, understanding the internal structure and working principle of gate valves is of great significance for correct selection, installation, and maintenance.

During the long-term service to industrial customers, we have found that many users often use gate valves but do not have a deep understanding of their working mechanism, which often leads to improper selection or inadequate maintenance.

I. Basic structure of gate valves

Gate valves are mainly composed of valve bodies, gate plates, valve stems, valve covers, seals, and operating mechanisms. The valve body is the main body of the gate valve, forming a fluid channel inside. The gate is the core opening and closing component, which opens and closes the valve by moving up and down. The valve stem is responsible for transmitting the operating torque and driving the gate movement. The valve cover is connected to the valve body to form a complete cavity. Seals ensure that the valve does not experience internal leakage when in the closed state.

1. Valve body

Valve bodies are usually manufactured using casting technology, and materials such as cast iron, cast steel, stainless steel, etc. can be selected according to different operating conditions. The internal flow channel design of the valve body directly affects the magnitude of fluid resistance. High quality gate valve body flow channels are smooth, which can minimize pressure loss to the greatest extent possible.

2. Gate plates

The gate is the core component of the gate valve to achieve the cutoff function. According to different structural forms, gate plates can be divided into two categories: wedge type and parallel type. Wedge gate relies on inclined surfaces to achieve sealing, making the sealing performance more reliable.  The parallel gate is assisted by medium pressure for sealing, suitable for medium and low pressure conditions.

3. Valve stems

The valve stem is divided into two forms: visible stem and hidden stem. The valve stem of a rising stem gate valve will move up and down during the opening and closing process, and the operator can intuitively judge the degree of valve opening. The stem of the concealed stem gate valve does not move up or down, making it more compact in structure and suitable for situations with limited installation space.

II. Working principle of gate valves

The working principle of a gate valve can be summarized as follows: by driving the valve stem to rotate or lift through the operating mechanism, the gate plate moves vertically in the valve body channel, thereby achieving on/off control of the pipeline medium. When the gate valve is fully open, the gate valve is completely lifted above the valve body cavity, and the medium can pass through without obstruction. When the gate valve is closed, the gate plate descends to the valve seat position, and sealing is achieved through the tight fit between the gate plate and the valve seat.

1. Opening process

The operator rotates the handwheel clockwise or counterclockwise (depending on the design), and converts the rotational motion into linear motion of the valve stem through the valve stem nut or similar transmission mechanism. The valve stem drives the gate to rise uniformly, gradually clearing the fluid channel. It should be noted that the torque of the gate valve will change during the opening process. The torque is maximum when it is first opened, and gradually decreases as the opening degree increases.

2. Closing process

When closing the gate valve, the operation direction is opposite to the opening direction. The valve stem drives the gate to descend, ultimately coming into contact with the valve seat and forming a seal. In the final stage of closure, it is necessary to apply appropriate torque to ensure that the sealing surface is fully adhered, but also to avoid excessive force causing damage to the sealing surface.

3. Sealing mechanism

The sealing of gate valves mainly relies on the tight contact between the gate and the sealing surface of the valve seat. The high-quality gate valve products use precision machined sealing surfaces and suitable sealing materials to maintain good sealing performance under high pressure differential conditions. Some high-performance gate valves also adopt an elastic gate design, which can automatically compensate for the wear of the sealing surface.

III. The main types of gate valves

Gate valves can be classified into various types based on their structural characteristics and usage scenarios. Understanding the characteristics of these types can help engineers make more appropriate choices in specific projects.

1. Wedge gate valves

The gate of a wedge gate valve is wedge-shaped, and sealing is achieved by the wedge-shaped fit between the gate and the valve seat. This type of gate valve has good sealing performance and is suitable for high pressure and high temperature conditions. It is the most common type of gate valve in industrial pipelines. According to the different numbers of gate plates, they can be divided into subtypes such as vertical single gate plates and double gate plates.

2. Parallel gate valves

The sealing surfaces of the gate and seat of a parallel gate valve are parallel to each other, and the sealing is achieved by medium pressure or spring force. This type of gate valve has a relatively simple structure, small opening torque, and is suitable for medium and low pressure, large-diameter applications. It is widely used in water supply and drainage engineering and urban pipeline networks.

IV. Application scenarios of gate valves

Gate valves are widely used in various industrial pipeline systems due to their excellent cutting performance and low flow resistance. In petrochemical plants, gate valves are commonly used in process pipelines that require full bore flow. In the power system, gate valves are an important component of the main steam and feedwater pipelines. In the field of municipal engineering, large-diameter gate valves are key control equipment for water supply pipelines.

We can provide targeted gate valve product solutions for users based on the application characteristics of different industries, ensuring stable and reliable operation of the products in actual working conditions.

V. Key parameters for selecting gate valves

When choosing a gate valve, it is important to consider the following parameters: nominal pressure, nominal diameter, applicable temperature, connection type, valve body material, and sealing surface material. The nominal pressure determines the pressure bearing capacity of the valve and must be matched with the design pressure of the pipeline system. The nominal diameter should be consistent with the diameter of the pipeline. The applicable temperature range covers the highest and lowest ambient temperatures at which the valve can operate normally. The main connection forms include flange connection, butt welding connection, and threaded connection, which need to be determined according to the pipeline installation method.

In addition, the characteristics of the medium are also factors that cannot be ignored when selecting. For corrosive media, gate valves made of corrosion-resistant materials should be selected. 

For media containing particles, the wear resistance of the gate and valve seat needs to be considered. The professional technical team can assist in the selection calculation and technical confirmation of gate valves based on the operating parameters provided by users.

FAQ

Q: Can gate valves regulate flow?

Answer: Gate valves are designed for fully open or fully closed states and are not suitable for flow regulation. If operated in a semi-open state for a long time, the high-speed flowing medium will erode the sealing surfaces of the gate and valve seat, leading to a decrease in sealing performance or even failure.

Q: How to choose between rising stem gate valve and hidden stem gate valve?

Answer: The rising and falling movement of the valve stem of the open stem gate valve is convenient for observing the degree of valve opening, and is suitable for outdoor or spacious occasions. The concealed stem gate valve has a compact structure and the valve stem does not rise or fall, making it suitable for applications with limited installation space or underground pipe galleries.

Q: Do I need to pay attention to the direction when installing gate valves?

Answer: Most gate valves are designed with bidirectional sealing, allowing the medium to flow in both directions without directional requirements during installation. But it is recommended to install in the direction indicated on the valve body to ensure optimal performance.

Q: Why is there still leakage after the gate valve is closed?

Answer: Possible reasons include: wear or foreign objects on the sealing surface, poor fit between the gate and valve seat, incomplete valve closure, or improper selection of sealing surface materials. It is recommended to promptly inspect and contact professional personnel for maintenance and handling.

Q: What are the daily maintenance contents of gate valves?

Answer: Regularly check whether the valve opens and closes flexibly, check whether the packing box leaks, keep the outside of the valve body clean, and regularly move the valve to prevent it from getting stuck. For gate valves that have not been operated for a long time, it is recommended to perform opening and closing operations at regular intervals.