Take you to fully understand globe valves

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　　The closing element of a globe valve is a plug-shaped disc, whose sealing surface is either flat or conical; the disc moves in a straight line along the centerline of the fluid. The movement pattern of the valve stem can be of the lift-type (where the valve stem moves up and down while the handwheel does not move), or it can be of the lift-rotate type (where both the handwheel and the valve stem rotate and move up and down, with the nut located on the valve body). 　　Globe valves are classified as forcibly sealed valves; therefore, when the valve is closed, pressure must be applied to the valve disc to ensure that the sealing surface does not leak. When the medium enters the valve from below the valve disc, the resistance that the operating force must overcome consists of the friction between the valve stem and the packing, as well as the thrust generated by the pressure of the medium. The force required to close the valve is greater than that needed to open it; therefore, the diameter of the valve stem must be large, otherwise the valve stem may bend. In recent years, since the advent of self-sealing valves, the flow direction of the medium in globe valves has changed to enter the valve chamber from above the valve disc. As a result, under the pressure of the medium, the force required to close the valve is smaller, while the force required to open it is greater; consequently, the diameter of the valve stem can be reduced accordingly. At the same time, under the influence of the medium, this type of valve is also more airtight. China’s regulations on valve design specified that for globe valves, the flow direction should always be from top to bottom. 　　According to the position of the valve stem thread, stop valves are divided into external-thread type and internal-thread type. Classified by the flow direction of the medium, there are straight-through type, direct-current type, and angled type. Based on the sealing type, globe valves are divided into gland-sealed globe valves and diaphragm-sealed globe valves. Installation and maintenance of globe valves: Globe valves operated by handwheels or handles can be installed at any position in the pipeline. Handwheels, handles, and actuating mechanisms must not be used for lifting purposes. The flow direction of the medium should be in line with the arrow indicated on the valve body. 　　When the globe valve is opened, when the opening height of the valve disc reaches 25%–30% of the nominal diameter, the flow rate has reached its maximum, indicating that the valve is in its fully open position. Therefore, the fully open position of the stop valve should be determined by the travel of the valve disc. Globe valves have the following advantages: 1. They have a simple structure, making them easy to manufacture and maintain. 2. The working stroke is small, and the opening and closing time is short. 3. It has good sealing performance, low friction between the sealing surfaces, and a long service life. The disadvantages of globe valves are as follows: 1. High fluid resistance, and significant force is required to open and close them. 2. Not suitable for media containing particles, with high viscosity, or prone to coking. 3. The regulation performance is poor. 　　According to the position of the valve stem thread, stop valves are divided into external-thread type and internal-thread type. Classified by the flow direction of the medium, there are straight-through type, direct-current type, and angled type. Based on the sealing type, globe valves are divided into gland-sealed globe valves and diaphragm-sealed globe valves. Installation and precautions for globe valves: 1. Globe valves operated by handwheels or handles can be installed at any position in the pipeline. 2. Handwheels, handles, and actuating mechanisms shall not be used for lifting purposes. 3. The flow direction of the medium should be consistent with the arrow indicated on the valve body. Structural features of the globe valve: 1. The internal chamber of the valve features a pressure-self-sealing structure, resulting in excellent sealing performance. 2. The sealing surfaces of the valve disc and seat are made by spray welding Stellite cobalt-based superalloys, offering good wear resistance, high-temperature resistance, corrosion resistance, and scratch resistance. 3. It is designed to resist high-temperature creep. 4. The valve stem has an integrally forged structure and undergoes quenching and tempering as well as surface nitriding treatment, giving it good corrosion resistance and scratch resistance. 5. The depth of the valve cover packing box is optimized; the packing contains corrosion inhibitors, ensuring reliable sealing. It is suitable for use in pipelines in power plants, petrochemical industries, metallurgy, and other fields where high temperatures and pressures are present, for shutting off or connecting fluids such as water, steam, oils, and superheated steam.