Perhaps there is a way to connect a valve that you don't know about.

2025-06-12 08:05:30

The selection of valve connection methods is crucial for the final type selection and application of valves. Different connection methods have distinct characteristics, and a thorough understanding of connection methods can help us gain in-depth knowledge of valves.   Common connection methods: Flange connection, wafer connection, butt-welding connection, threaded connection, compression fitting connection, clamp connection, self-sealing connection, etc.

Have we grasped the全貌 (overview) of these valve connection methods? 

Flange Connection  

The valve body has flanges at both ends, corresponding to the flanges on the pipeline, and is installed in the pipeline by fixing the flanges with bolts. Flange connection is the most widely used connection form in valves. Flanges include raised face (RF), flat face (FF), male and female face (MF), etc.  

According to the shape of the joint surface, it can be divided into the following types:   

1. Smooth type: Used for valves with low pressure, easy to process.   

2. Male and female type: Suitable for higher working pressure, can use medium-hard gaskets.   

3. Tongue and groove type: Can use gaskets with large plastic deformation, widely used in corrosive media, with good sealing effect.   

4. Trapezoidal groove type: Uses elliptical metal rings as gaskets, suitable for valves with working pressure ≥ 64 kg/cm² or high-temperature valves.   

5. Lens type: The gasket is lens-shaped and made of metal, used for high-pressure valves with working pressure ≥ 100 kg/cm² or high-temperature valves. 

6. O-ring type: A relatively new flange connection form developed with the emergence of various rubber O-rings, which is more reliable in sealing effect than ordinary flat gaskets.  

Wafer Connection   

The valve is installed between two flanges, and the valve body usually has positioning holes for easy installation and positioning. It is connected by directly clamping the valve and the pipelines at both ends together with bolts.

 Welding Connection   

Both ends of the valve body are processed into butt-welding grooves according to butt-welding requirements, corresponding to the welding grooves of the pipeline, and fixed on the pipeline by welding.  

Socket Welding Connection   

Both ends of the valve body are processed according to socket welding requirements, and connected to the pipeline through socket welding.  

Threaded Connection   

Threaded connection is a simple connection method, commonly used for small valves. The valve body is processed according to each thread standard, with two types: internal thread and external thread, corresponding to the threads on the pipeline.   

Threaded connection is divided into two cases:   

1. Direct sealing: The internal and external threads directly play a sealing role. To ensure no leakage at the connection, lead oil, linen thread, and PTFE thread seal tape are often used for filling; among them, PTFE thread seal tape is increasingly widely used. This material has excellent corrosion resistance, excellent sealing effect, and is convenient to use and store. When disassembling, it can be removed intact because it is a layer of non-sticky film, much superior to lead oil and linen thread.   

2. Indirect sealing: The force of thread tightening is transmitted to the gasket between the two planes, allowing the gasket to play a sealing role. Common threads include five categories: metric common thread; British common thread; threaded sealed pipe thread; non-threaded sealed pipe thread; American standard pipe thread.  

Compression Fitting Connection   

It has only developed in China in recent years. Its connection and sealing principle is that when the nut is tightened, the compression ring is under pressure, causing its blade to bite into the outer wall of the pipe, and the outer conical surface of the compression ring is closely fitted with the inner conical surface of the joint body under pressure, thus reliably preventing leakage (e.g., instrument valves). The advantages of this connection form are:   

- Small volume, light weight, Simple Structure, and easy disassembly and assembly.   

- Strong connection force, wide application range, resistant to high pressure (1000 kg/cm²), high temperature (650℃), and impact vibration.   

- Multiple materials can be selected, suitable for anti-corrosion.   

- Low requirement for machining accuracy.   

- Convenient for high-altitude installation. Currently, compression fitting connection has been adopted in some small-diameter valve products in China.  

Clamp Connection  

This is a quick connection method that requires only two bolts, suitable for low-pressure valves that need frequent disassembly (e.g., sanitary valves).  

Internal Self-Tightening Connection  

The above connection forms all use external force to offset the medium pressure for sealing. The following introduces a connection form that uses medium pressure for self-tightening. Its sealing ring is installed at the inner cone, forming a certain angle with the side facing the medium. The medium pressure is transmitted to the inner cone and then to the sealing ring, generating two component forces on the conical surface at a certain angle: one is parallel to the valve body centerline and outward, and the other presses against the inner wall of the valve body. The latter component force is the self-tightening force. The greater the medium pressure, the greater the self-tightening force. Therefore, this connection form is suitable for high-pressure valves. It saves much material and manpower compared to flange connection but also requires a certain pre-tightening force to ensure reliability when the internal pressure of the valve is low.   

Valves made using the self-tightening sealing principle are generally high-pressure valves.   

There are many other valve connection forms, such as small valves that do not need to be disassembled and are welded to the pipeline, or non-metallic valves using socket connection, etc. Valve users should handle specific situations accordingly.