Basic Valve Knowledge

1. The Function of Valves

A valve is a device used in piping systems to control the flow of liquids or gases. Its main functions are:

1. On/Off Function: Like a faucet, it controls the start and stop of fluid flow, enabling control over the pipeline system.
2. Flow Regulation: By changing the degree of valve opening, it controls the flow rate of the fluid within the pipe.
3. Safety Protection: Valves also have safety functions such as preventing backflow of the medium (e.g., check valves) and overpressure relief (e.g., safety valves), ensuring the safe operation of the pipeline system.

2. Classification of Valves

Valves can be classified in various ways, according to different standards, as follows:

1. By Function: Isolation valves (e.g., gate valves, globe valves), regulating valves, check valves, and safety valves.
2. By Structure: Ball valves, butterfly valves, gate valves, etc. Different valve structures are suitable for different application scenarios.
3. By Actuation Method: Manual, electric, and pneumatic, etc. The higher the degree of automation, the more convenient the operation.

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Six Common Types of Valves

Next, we will introduce in detail the working principles and applicable scenarios of six common types of valves.

1. Gate Valve: The Gateway in a Pipeline

Working Principle: A gate valve achieves full opening or full closing by lifting or lowering a gate. The gate moves along the axis of the valve body. When the gate is fully closed, the medium flow is cut off; when the gate is fully open, the medium flows through without obstruction, similar to the principle of a sliding door.

Characteristics: Extremely low flow resistance when fully open, suitable for scenarios requiring straight-through flow; slow opening and closing speed, not suitable for frequent operation.

2. Globe Valve: The Expert in Precise Flow Regulation

Working Principle: A globe valve regulates the flow area by the vertical movement of a disc. Its opening and closing part is a cylindrical disc with a sealing surface designed as a flat or conical structure. The disc moves linearly along the centerline of the fluid to achieve opening and closing. When the handwheel is rotated, the stem rises or falls accordingly, driving the disc to move parallel to the medium flow direction, thus controlling the valve's open and closed state.

Characteristics: Good sealing performance, relatively high flow resistance. Attention must be paid to the "low-in, high-out" direction during installation. Suitable for occasions requiring frequent flow regulation.

3. Ball Valve: The Fast-Acting Rotation Expert

Working Principle: A ball valve controls the flow of fluid by rotating a ball (the ball core). When the ball's port is aligned with the pipeline, fluid can pass freely; when the ball is rotated so the port is perpendicular to the pipeline, the fluid is completely blocked.

Characteristics: Quick opening and closing, good sealing performance, high pressure resistance. The sealing surface is prone to wear, making it unsuitable for fluids containing impurities.

4. Butterfly Valve: The Energy-Saving Choice for Large-Diameter Pipelines

Working Principle: A butterfly valve controls the flow rate of the medium through the rotation angle of the disc, typically between 0° and 90°. The flow rate changes in a roughly linear proportion to the angle; the larger the angle, the greater the flow.

Characteristics: Small size and light weight, suitable for large pipe diameters. Regulation accuracy is relatively low, but it performs better in low-pressure differential scenarios.

5. Check Valve: The Guardian Against Backflow

Working Principle: A check valve relies on the pressure of the medium itself to open and close, preventing fluid from flowing backward.

Common Types: Lift check valve and swing check valve. Lift check valves are commonly used in vertical pipelines, while swing check valves are often used in horizontal pipelines.

6. Safety Valve: The "Safety Barrier" of Pressure Systems

Working Principle: If the system pressure rises to exceed a predetermined threshold, the safety valve will automatically activate to relieve pressure, thereby ensuring the pipeline system is not damaged.

Key Parameters: Set pressure (popping pressure), reseating pressure, and relieving capacity.

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From the above, it is easy to see that valves are key devices for controlling medium flow. Therefore, during the selection, installation, and maintenance of valves, we must strictly adhere to relevant specifications and standards.

During installation, attention must be paid to the valve's installation direction, support structure, and cleanliness inside the pipeline to avoid valve failures caused by improper installation. In daily maintenance, we should regularly check the valve's sealing performance, lubrication status, and whether there is any accumulation of impurities, ensuring the valve remains in good working condition. It is hoped that everyone will deeply recognize this and implement it diligently in their practical work.