Globe valve basics

The opening and closing part of the stop valve is a plug-shaped valve flap, and the sealing surface is a plane or a cone surface, and the valve flap moves linearly along the centerline of the fluid. The valve stem is in the form of a lifting rod (the stem moves up and down, the hand wheel does not lift), and there is also a lifting and rotating rod type (the hand wheel rotates and lifts together with the valve stem, and the nut is arranged on the valve body). Shut-off valves are only suitable for full opening and full closing and do not allow adjustments and throttling. The shutoff valve is a forced seal type valve, so when the valve is closed, pressure must be applied to the valve flap to force the seal surface not to leak. When the medium enters valve 6 from below the valve flap, the resistance to be overcome by the operating force is the friction force of the stem and packing and the thrust generated by the pressure of the medium. The force of closing the valve is greater than the force of opening the valve, so the valve The diameter of the rod must be large, otherwise a failure of the stem bending may occur. In recent years, after the emergence of the self-sealing valve, the medium flow of the stop valve has been changed from above the valve flap into the valve chamber. At this time, under the pressure of the medium, the force to close the valve is small, and the force to open the valve is large. The diameter can be reduced accordingly. At the same time, this type of valve is also tighter under the influence of the medium. China's valve "three to give" has stipulated that the flow direction of the globe valve shall be adopted from top to bottom. When the stop valve is opened, the opening height of the valve flap is 25% to 30% of the nominal diameter, and the flow rate has reached the maximum, indicating that the valve has reached the fully open position. Therefore, the fully open position of the stop valve should be determined by the stroke of the disc.

Globe valves have the following advantages:
1, simple structure, manufacturing and maintenance more convenient.
2, the work schedule is small, opening and closing time is short.
3, good sealing, low friction between the sealing surface, long life.

The disadvantages of the globe valve are as follows:
1. The fluid resistance is large, and the force required when opening and closing is large.
2, does not apply to particles, viscosity, easy to coke the medium.
3, poor regulation performance.

The type of globe valve is divided into male thread type and female thread type according to the position of the stem thread. According to the flow direction of the media, there are straight-through, direct-flow, and angled. The shut-off valve is divided according to the form of the seal. There are packing seal cut-off valve and bellows sealed shut-off valve.

For the installation and maintenance of globe valves, please note the following:
1. The handwheel and handle operated stop valve can be installed anywhere on the pipe.
2. Handwheels, handles and vigor mechanisms shall not be used for hoisting.
3, the direction of flow of the medium should be consistent with the direction of the arrow shown in the valve body.