Straight-through globe valve relies on the pressure of the valve stem so that the sealing surface of the valve flap and the sealing surface of the valve seat are closely combined to stop the flow of media. In the opening and closing process between the sealing surface, friction is small, wear-resistant, small opening height, good manufacturing process performance, and other characteristics. Compared with the gate valve, the structure of the globe valve is simpler, and manufacturing and maintenance are more convenient. The seal surface is not easy to wear, abrasion, sealing performance is better, longer life. Smaller flap stroke when opening and closing, shorter opening and closing time.
Die-forged valve body or free forging valve body will usually import and export channels and pipeline centerline at an angle, that is, to form a Z-shaped flow channel, and often processed to reduce the diameter, however, the reduced aperture and zigzag flow channel will greatly increase the fluid pressure loss, in addition, it should be noted that the sharp angle of the turn in the fluid service will have cavitation phenomenon.
2. Angular globe valve
Tracing the history of the development of the globe valve, the initial development of the angular globe valve, and then gradually developed into a straight-through globe valve. Today, although the straight-through globe valve is more commonly used, the angle globe valve still has some unique advantages.
Angle shut-off valve opening and closing member is a plug-shaped valve, sealing surface is flat or tapered, the valve along the centerline of the fluid for linear motion. The movement of the valve stem in the form of a lift rod (stem lift, handwheel does not lift), but also lift rotary rod (handwheel and stem together with the rotation of lift, the nut is located on the valve body). Angle shut-off valve open, the opening height of the valve flap, 25% to 30% of the nominal diameter, the flow has reached the maximum, that the valve has reached the fully open position.
Small copper alloy threaded connection angle shut-off valves are widely used in clean water service. Most industrial angle globe valves are of the bolted bonnet type and are manufactured in cast steel, but bronze, stainless steel, and duplex materials are also used.
Angular globe valves are commonly available in sizes and pressure ratings from DN50 to 250 (NPS 2 to 10) and Class 150 to 800, beyond which balanced flaps are often used to reduce the axial thrust of the fluid on the stem.
A Three-way globe valve is usually used in a high-pressure system as a reversing valve. Such as power station boiler high temperature and high-pressure water supply valve. Reversing is usually used for start-up, shutdown, or failure time.
Another more common application as a reversing valve is a pressure relief system. Two safety valves are mounted on a three-way shut-off valve so that when one of the safety valves needs to be isolated or repaired, the other one can operate normally. Due to the internal structure, the three-way shut-off valve has a high flow resistance. The change of fluid direction will cause a large reaction force on the large diameter three-way globe valve.
Three-way globe valve bodies are generally cast steel or alloy steel. Valves used in power plants generally have butt-welded connections to overcome the problem of leakage that can occur with flanged connections.
4. Direct current type globe valve
DC globe valve is also known as a Y-shaped globe valve or oblique globe valve, which can become an intermediate state between straight-through and angle-type valves. In order to change the straight-through zigzag fluid passage, the seat hole and the valve body are designed at an angle so that the flow path becomes more straight with the axis to reduce pressure loss, so-called “DC”. This structure is popular in most applications and is used in steam systems. DC type fluid resistance is small and solids transfer capability has been greatly improved, mostly used for fluids containing solid particles or high viscosity.
Valves with flat flaps and valves with claw-guided flaps can be fitted with a wiper to clean the valve seat before sealing or with a rubber seal to improve the sealing performance of the valve.
The direct flow globe valve is usually cast and forged for high-pressure valves. According to the needs of different working conditions, such duplex stainless steel and other special materials can be used to manufacture.
5. Bellows sealed globe valve
The bellows-sealed globe valve is shown in the figure above. The bellows globe valve is mainly a packing seal replaced by a bellows seal. The upper part of the outer surface of the bellows is welded together with the valve body so as to form a confined space, and the liquid is in this confined space. The stem is inserted inside the bellows, the bottom of the bellows is connected to the spool, and the bellows expand and contract to control the opening of the spool. So there is no leakage if the bellows are not cracked. Bellows seal reliability is very high and can be used in toxic media or gas. Such as chlorine gas. To prevent leakage.
Bellows disconnecting valve is suitable for petroleum, chemical, pharmaceutical, fertilizer, electric power, and other industries in a variety of working conditions on the pipeline, used to cut off or connect the pipeline medium.
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