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Bellows-Sealed Valves Explained

FITOK Bellows-Sealed Valve

 

Overview

 

 

As manufacturing processes become increasingly precise, users of instrumentation valves and fittings are placing higher demands on product performance. In addition to standardized material selection, accurate opening and closing, and clean flow paths, critical performance indicators—such as leakage rates—are becoming more stringent. Bellows-sealed valves use a metal bellows as the stem sealing element. The bellows compresses and expands as the stem moves, forming a reliable dynamic seal. As a result, bellows-sealed valves are particularly well suited for applications involving toxic, flammable, explosive, or other hazardous media, as well as systems where pipeline sealing integrity is critical. These valves are widely used in semiconductor manufacturing, fine chemical processing, pharmaceuticals, nuclear power, vacuum systems, and low temperature applications.

 

FITOK Bellows-Sealed Valve Used in Semiconductor Manufacturing Toxic Gas Lines

 

Figure 1: FITOK Bellows-Sealed Valve Used in Alkane Gas Lines

 

In piping systems, ball valves, needle valves, diaphragm valves, and bellows-sealed valves are all commonly used as globe valves; however, their sealing structures and performance characteristics differ significantly. Ball valves and needle valves typically rely on packing seals, which may generate particulates due to wear during frequent operation and usually require periodic adjustment to maintain sealing performance. By contrast, bellows-sealed valves employ welded metal bellows or metal gasket sealing structures, eliminating the need for routine seal maintenance. They are suitable for more extreme temperature conditions and provide cleaner flow paths. While diaphragm valves offer advantages in cleanliness, bellows-sealed valves achieve comparable cleanliness while delivering superior flow characteristics and a much wider operating temperature range due to their all-metal sealing design.

 

Typical Structure of a Bellows-Sealed Valve

 

 

A bellows-sealed valve primarily consists of a valve body, bellows, stem tip, bonnet nut, stem, and operating mechanism (handle or actuator), as shown in Figure 2. The bellows—being the core sealing component—is typically manufactured from 300-series stainless steel to ensure long service life and excellent compatibility with a wide range of media.

 

The valve body serves as the main pressure-bearing component and is commonly made of stainless steel or brass. It provides the flow path and end connections for the process media. The lower stem transmits operating mechanism motion into precise linear movement, driving the stem tip to achieve accurate valve opening, closing, or flow regulation. Furthermore, the FITOK SU Series incorporates a bellows-plus-packing dual-seal configuration. In the event of primary seal (bellows) failure, this design helps prevent rapid leakage of media into the external environment.

 

Typical Structure of the FITOK SW Series Bellows-Sealed Valve

 

Figure 2: Typical Structure of the FITOK SW Series Bellows-Sealed Valve

 

FITOK Bellows-Sealed Valve Features and Advantages

 

 

The bellows is the heart of a bellows-sealed valve, and its quality directly determines valve reliability and service life. FITOK employs advanced manufacturing technologies to produce bellows with uniform wall thickness and optimized residual stress distribution, significantly improving flexibility and fatigue resistance.

 

FITOK bellows-sealed valves offer the following advantages:

 

  • Advanced welding processes to extend bellows service life.
  • 316L stainless steel bellows provide excellent chemical compatibility and media purity, with optional alloy bellows available for highly corrosive media.
  • High sealing performance, with a maximum helium leak rate of 4 × 10⁻⁹ std·cm³/s.
  • Multiple series covering a wide range of working pressures, up to 3500 psig.
  • Extensive design and manufacturing expertise to ensure consistent product quality.
  • Broad application experience and one-stop fluid system solutions.

FITOK Bellows-Sealed Valve Used in High-Purity Gas Lines

 

Figure 3: FITOK Bellows-Sealed Valve Used in High-Purity Gas Lines

 

FITOK currently offers four series of bellows-sealed valves: SW, SU, SM, and SVH.Their key parameters are summarized in Table 1, providing solutions for a wide range of operating conditions and application requirements.

 

Table 1: Comparison of Main Parameters for FITOK Bellows-Sealed Valves

 

Table 1: Comparison of Main Parameters for FITOK Bellows-Sealed Valves

 

With their low leakage rates, long service life, and ease of maintenance, FITOK bellows-sealed valves have become a preferred choice across a wide range of industries.Through continuous technological innovation and rigorous quality control, FITOK delivers reliable sealing solutions that provide robust protection for the most demanding applications.

 

For more information, please refer to the bellows-sealed valves catalog. Should you have any questions, please leave a message online, and we will reach you as soon as possible!

Next：Floating Ball Valves vs. Trunnion Ball Valves
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