What is the difference between a stop valve and a gate valve?
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With the development of society, the demand for valves is increasing steadily. Whether in construction, industry, or people’s daily lives, valves can be seen everywhere, and their role has become absolutely essential. Similarly, as their applications become more widespread, there are also more manufacturers of valves, and the range of products developed and produced is increasing. Among these, globe valves and gate valves are two of the most popular types within the valve family. I. Structural principle of globe valves: Principle Globe valves are among the most widely used types of valves, and they are very popular among users. During operation, the globe valve does not generate excessive frictional pressure, ensuring reliable sealing performance and long durability. Its simple design leads to significant cost savings. This valve can be used in both low-pressure and high-pressure applications. The closing element of a globe valve is a plug-shaped disc that moves along the center line of the valve body; the pressure applied by the valve stem enables the disc to fit tightly against the sealing surface of the valve seat. The flow direction of a globe valve is fixed. The regulations regarding valves in China stipulate that the flow direction of globe valves should always be from top to bottom; therefore, they must be installed in accordance with these requirements. Structural diagram: http://www.cnbgfm.com/includes/editor/attached/image/20141215/20141215020909_67524.jpg II. Structural principle of gate valves: Principle Gate valves are types of valves that provide automatic sealing. Traditional gate valves generally use a forced-sealing mechanism. With the advancement of valve technology, modern gate valves can rely on the pressure generated by the flow of the medium to press the sealing surface against the seating surface on the other side, thereby bringing the two sealing surfaces into close contact and ensuring good sealing – this is what is known as self-sealing in gate valves: http://www.huaguangv.com The closing element of a gate valve is the gate, which can only be in a fully open or fully closed position. The direction of movement of the gate is perpendicular to the direction of flow of the medium. The gate valve moves in a straight line along with the valve stem; typically, the lift rod is equipped with triangular threads. These threads convert rotational motion into linear motion through the nut located at the top of the valve and the guide groove above the valve body. In simple terms, this process converts the operating torque into an operating thrust. Structural diagram: http://www.cnbgfm.com/includes/editor/attached/image/20141215/20141215020849_76217.jpg III. Differences between globe valves and gate valves: What are the differences between globe valves and gate valves? They can be determined based on the following points. ①Sealing surface: The sealing of a globe valve is mandatory; pressure from an external source is required to achieve sealing. In a fully closed state, the valve plug of a globe valve comes into contact with the sealing surface. However, since there is little contact between them, the amount of relative sliding is small, so wear on the sealing surface is minimal. Most wear on sealing surfaces is caused by high-speed flow of the fluid and impurities present on the sealing surface itself. A gate valve, on the other hand, is self-sealing; it relies on the pressure generated by fluid flow to press the sealing surface against that of the valve seat, ensuring a tight fit between them. ②Flow direction: In accordance with **regulations**, the flow in globe valves must be from top to bottom; gate valves, on the other hand, have no specific requirement regarding the direction of inlet or outlet. ③Coefficient of resistance: The coefficient of resistance for ordinary globe valves is approximately 3.5 to 4.5. The flow resistance coefficient of a standard gate valve is approximately 0.08~0.12. Summary of differences: Compared to gate valves, globe valves are simpler and lighter, have better sealing performance, and are easier to maintain; however, gate valves have a shorter opening and closing stroke, operate faster, and experience less resistance from the fluid. Both of these types of valves are designed for full open or full closed operation; they cannot be used to regulate the flow of fluid, but only to shut off or connect the medium. Nevertheless, they have a very wide range of applications, serving as control devices in pipelines carrying air, water, steam, various corrosive substances, mud, oils, and other fluids.
Thank you to the original poster for sharing! My understanding of gate valves and globe valves has improved, especially regarding the issue of self-sealing in gate valves. May I ask when approximately the transition period between forced sealing and self-sealing technologies took place? In recent years, we have used some gate valves equipped with electric actuators as shut-off valves, and overall the results have been good; this approach has solved some problems associated with the improper use of triple-eccentric butterfly valves in certain applications. At the same time, self-sealing will reduce the output force of the actuator, thereby lowering costs.
What does it mean that for globe valves, the flow of the medium must be from top to bottom?
Medium flow requires a top-to-bottom direction, as can be seen from the structural diagram; however, there are also cases where it flows bottom-to-top.
Spherical valve (gate type): The valve stem drives the valve core to move up and down in a straight line, and overcoming significant unbalanced forces is required to open or close the valve. It is mainly used for the rapid on/off control and regulation of fluids. Due to the fluid redirection, there is a significant pressure drop; it is suitable for gases, and especially appropriate for steam. The actuator and operation method can be manual, electric, pneumatic, or hydraulic. It is typically used in high-pressure or high-flow systems, and due to cost reasons it is rarely used with fibrous, viscous, or contaminated fluids. Plunger valve: Plunger valves are generally suitable for full-open or full-closed operation; they can be used with various fluids, and are especially appropriate for fluids that cause wear on valve seats. They are usually operated manually, with a small number of electric and pneumatic versions available. It is usually used in places where it is used for a long time with little maintenance. Globe valve: The valve stem of a globe valve drives the valve disc to move up and down in a straight line; when fully open, it causes little disturbance to the fluid, resulting in very low pressure drop ； Triple-sealed, with poor sealing performance and prone to leakage ； It requires a lot of maintenance and has a large travel distance; it usually cannot be opened partially. It is mainly used for fluids with high viscosity, as well as large-diameter steam systems of DN200 and above. It is not recommended for use in throttling; solid wedge gate valves are not affected by vibrations caused by the fluid, while double-sided parallel gate valves are commonly used in steam systems.
Gate valves are generally installed from bottom to top; only large-diameter gate valves, considering the torque required for closing and the forces acting on the valve stem, use a top-to-bottom design and installation method. The gate valve shown in the image above should be referred to as a single-sided forced-seal type, while self-sealing relates to the sealing that prevents leakage from the internal chamber
The explanation was very detailed and meaningful
It should generally be bottom-up, rather than being mandated to be top-down
Most globe valves are installed from bottom to top; only those with large diameters are installed from top to bottom
Can a stop valve also regulate flow?
In practical use, globe valves can also be used to regulate pressure or flow, but this is done on a rough level; generally, globe valves are not used for precise regulation purposes.