Metal Bellows Sealed Valves
Metal Bellows Sealed Valves are type of valve that incorporates a metal bellows assembly into the stem system, serving as the primary dynamic sealing element. Its core design objective is to achieve absolute zero leakage at the valve stem to meet the most demanding operational requirements.
Core Structure and Working Principle
Structure:
The metal bellows is a flexible sealing element capable of axial compression and extension.
One end is welded to the valve body or bonnet, and the other end is welded to the valve stem, forming a all-metal sealed barrier.
This structure completely isolates the valve stem from the process medium.
Working Principle:
When operating the valve (opening or closing), the valve stem moves up and down or rotates.
At this time, instead of the valve stem sliding within a stuffing box, the metal bellows undergoes compression, extension, or torsional elastic deformation to accommodate the stem's movement.
Consequently, the process medium is entirely confined within the valve body cavity and the bellows chamber, fundamentally eliminating any possibility of leakage through the stem packing.
Main Types
The bellows seal design can be applied to various types of valves, the most common being:
Bellows Sealed Globe Valve
The most common type. Utilizes the bellows to seal the stem, while relying on the contact between the disc and seat for shut-off sealing. Suitable for applications requiring precise flow control and absolute sealing.
Bellows Sealed Gate Valve
Integrates a bellows into the stem area of a gate valve. Due to the long stroke of gate valves, the requirements for the bellows' stroke and fatigue life are extremely high. Primarily used for fully open/fully closed applications demanding zero leakage.
Bellows Sealed Ball Valve
A more high-end design. Often employs a "bellows + packing" dual-seal arrangement, providing an additional safety layer for ball valves handling extremely hazardous media.
Bellows Sealed Control Valve
Used in automated process control applications where precise flow control is required and medium leakage is unacceptable.
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