Introduction to the Advantages and Disadvantages of Bellows Globe Valves

Release date:

2021-02-08

The opening and closing part of the bellows globe valve is a plug-shaped disc, with the sealing surface being flat or conical. The disc moves linearly along the fluid centerline. The valve stem movement types include rising stem (the stem rises and falls, but the handwheel does not) and rising and rotating stem (the handwheel rotates and rises with the stem, with the nut mounted on the valve body). Globe valves are only suitable for fully open or fully closed positions and are not allowed for regulation or throttling.

The bellows globe valve is a forced sealing valve, so when the valve is closed, pressure must be applied to the valve disc to ensure the sealing surface does not leak. When the medium enters the valve from below the valve disc, the operating force must overcome the friction between the valve stem and packing as well as the thrust generated by the medium pressure. The force required to close the valve is greater than that to open it, so the valve stem diameter should be larger; otherwise, the stem may bend. In recent years, since the advent of self-sealing valves, the flow direction of the medium in bellows globe valves has changed from above the valve disc to inside the valve chamber. At this time, under the action of medium pressure, the force to close the valve is small, but the force to open it is large, allowing the valve stem diameter to be correspondingly reduced. Meanwhile, under the medium's effect, this valve is also relatively tight. China's valve "three-in-one" standard once stipulated that the flow direction of bellows globe valves should be from top to bottom.

When the bellows globe valve is opening, the flow reaches its maximum when the valve disc opening height is 25% to 30% of the nominal diameter, indicating that the valve has reached the fully open position. Therefore, the fully open position of the bellows globe valve should be determined by the stroke of the valve disc.

Advantages of bellows globe valves:

1. Simple structure, easy to manufacture and maintain.

2. Short working stroke, short opening and closing time.

3. Good sealing performance, low friction between sealing surfaces, and long service life.

Disadvantages of bellows globe valves:

1. High fluid resistance, requiring large force to open and close.

2. Not suitable for media with particles, high viscosity, or prone to coking.

3. Poor regulatory performance.

Types of bellows globe valves are divided based on the position of the valve stem thread into external thread type and internal thread type. According to the flow direction of the medium, there are straight-through, straight-flow, and angle types. Bellows globe valves are classified by sealing form, including packing-sealed globe valves and bellows-sealed globe valves.

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