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Large Caliber Bellow Globe Valves

Release time:

Aug 27,2024

large-diameter bellows globe valves are prone to instability during use due to the long bellows stroke, which causes friction between the inner wall of the bellows and the valve stem and affects the service life of the bellows. In addition, the flat key, which guides the stem to move axially and prevents the stem from rotating, is often easily damaged due to the increased vertical axial shear stress caused by excessive opening of the valve. According to the working conditions, a new type of large-diameter bellows globe valves is designed.

Large Caliber Bellow Globe Valves

1. Overview

In petroleum and chemical installations, in order to prevent the transmission of harmful, toxic or flammable liquid media leakage, pipeline often use bellows globe valves. However, large-diameter bellows globe valves are prone to instability during use due to the long bellows stroke, which causes friction between the inner wall of the bellows and the valve stem and affects the service life of the bellows. In addition, the flat key, which guides the stem to move axially and prevents the stem from rotating, is often easily damaged due to the increased vertical axial shear stress caused by excessive opening of the valve. According to the working conditions, a new type of large-diameter bellows globe valves is designed.

2. Structural characteristics

Large-diameter bellows globe valve is mainly composed of valve body, valve flap, valve stem, bellows and bonnet with stuffing box and other parts. Between the valve body and the bonnet there is an extension tube connected with a stud to form an extended valve cavity. The lower part of the valve stem is located in the valve cavity, and its end is secured to the valve flap by a counter nut. The upper part of the stem passes through the stuffing box on the bonnet, and the externally threaded portion of the upper part of the stem engages the stem nut. The stem nut is fixed in the seat hole of the upper part of the bonnet with a bearing and bearing gland connection. The handwheel is mated with the square head of the stem nut by a square hole. The stem lift is limited by the bonnet. The bonnet is connected to the top part of the stem nut with internal threads, and the bonnet, stem nut and handwheel are locked and fixed together with the round nut that engages with the external threads on the bonnet. The packing is placed in the packing box and pressurized by the packing gland to maintain the original packing seal of the globe valve and prevent leakage of the liquid medium.

1、Body   2、Plate   3、Shift   4、Bellows   5、Connecting flange  6、Flat key   7、Boneet     8、Packing    9、Hat of the cover

3. Performance

The large diameter bellows globe valve is a bellows assembly added to the stem part of the ordinary globe valve cavity to prevent stem seal failure. The bellows seal and packing seal work together to form a double seal, ensuring the reliability of the axial dynamic seal. Packing is prone to leakage during long time use, the design adopts loaded packing compression mechanism to make the packing seal more durable and reliable. The large diameter bellows globe valve adopts two sections of bellows in series, which not only ensures the stroke requirement, but also prevents the bellows from destabilizing. In order to prevent the bellows from twisting during the opening and closing of the valve, an anti-rotation flat key is set on the valve stem. The flat key has both anti-rotation and guiding functions. During the valve opening process, the flat key is subject to both the horizontal shear stress in the anti-rotation direction and the vertical shear stress in the restriction direction, which makes it extremely easy to be damaged. Therefore, a nut with a cap is added at the top of the valve stem to restrict the opening position of the valve and to reduce the force on the flat key.

4.Conclusion

By adopting the combination bellows, the large diameter bellows globe valve solves the problem of pipe wall abrasion caused by the instability of the bellows with too long a stroke, and also solves the problem of eliminating the axial vertical shear stress of the flat key.

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