When is a stop valve used?

Globe valves, like gate valves, have the function of shutting off flow, but they also offer a certain degree of regulation, whereas gate valves cannot regulate flow. Its structural design determines that its size cannot be too large; it is generally smaller than DN200. Gate valves, on the other hand, can be made quite large – I have even seen ones with a diameter of 3 meters – which is why gate valves are used for large-diameter pipes. Its structure is more complex than that of gate valves, with flow from bottom to top, which provides better sealing for the valve stem. However, it isn’t absolutely impossible to install it in reverse; for example, in the case of a sewage outlet on a pressure vessel that leads directly into a drain, where the inside of the vessel is under pressure while the discharge end is at atmospheric pressure, and such outlets are used infrequently. In such situations, the stop valve needs to be installed in reverse, as installing it in the normal orientation would cause the shaft seal to be under constant pressure and thus prone to leakage. The conditions under which reverse installation is possible are determined based on the characteristics of the stop valve. As for the issue of valves not sealing properly, this is not just a problem specific to globe valves; it’s an old issue with domestic valves. In chemical plants, it’s almost impossible to find valves that do not leak. Gate valves, which are used solely for shutting off flow rather than regulating it, are better than globe valves, as the fit between the valve core and the seat in globe valves may not be optimal. Of course, if precise control of flow is required, needle valves and control valves are better choices than flow stop valves.

Stop valves have the function of shutting off flow, but they also offer some degree of regulation; those with a diameter of less than 200 are generally used for gases, liquefied gases, and as branches in control valve systems

Control valves can be used to regulate flow rates; they are commonly employed in situations where frequent adjustment of flow is not necessary. For example, they are used on auxiliary lines, and their specifications generally do not exceed DN200, with larger sizes being more expensive.

Now, globe valves can be manufactured up to DN300, and many manufacturers are producing them

From an economic perspective, gate valves are cheap while globe valves are expensive~

Stop valves are generally used in pipelines with a nominal diameter of DN150 or less, and can serve to regulate flow rate to a certain extent

Stop valves can regulate flow, while gate valves are generally used in pipelines that need to be either fully closed or fully open, and are not used for regulating flow

In most cases, the function of a globe valve is to regulate flow, while the function of a gate valve is to shut off flow!

The closing element of a stop valve (or globe valve) is a plug-shaped valve disc, whose sealing surface is either flat or conical; the valve 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). Stop valves are only suitable for full open and full closed positions; they cannot be used for regulation or throttling. 　　Globe valves are classified as valves with forced sealing; 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. 　　When the globe valve is opened, the flow rate reaches its maximum when the opening height of the valve disc is 25% to 30% of the nominal diameter, indicating that the valve has reached its fully open position. Therefore, the fully open position of the stop valve should be determined by the travel of the valve disc. 　　Classification of globe valves 1. Based on the direction of the flow in the globe valve, they can be classified as: 1) Straight-through globe valves 2) Angle-type globe valves: In angle-type or Y-shaped globe valves, the flow channel within the valve body is at an angle to the main flow direction; this results in less disruption to the flow pattern compared to conventional globe valves, and consequently, the pressure loss across the valve is also lower. 　　3) Angle-type globe valve: In an angle-type globe valve, the fluid only needs to change direction once, resulting in a lower pressure drop across this valve compared to globe valves with conventional designs. 　　4) Plunger-type globe valve: This type of globe valve is a variant of the conventional globe valve. In this valve, the valve disc and seat are typically designed based on the plunger principle. The valve disc is polished to form a plunger that connects with the valve stem, and sealing is achieved through two elastic sealing rings fitted over the plunger. The two elastic sealing rings are separated by a collar, and the sealing rings surrounding the plunger are pressed firmly in place by the load applied to the valve cover by the valve cover nut. The elastic sealing ring can be replaced and is made from a variety of materials. This valve is primarily used for opening or closing, but it also features a specially designed plunger or special rings that allow for flow regulation. 　　2. Based on the position of the threads on the stem of the globe valve, they can be classified as: 1) Globe valves with upper-threaded stems: The threads on the stem of such globe valves are located outside the valve body. Its advantage is that the valve stem is not subject to erosion by the medium, making lubrication easier; this type of structure is quite commonly used. 　　2) Lower-threaded valve stem globe valve: The threads of the globe valve stem are located inside the valve body. In this type of structure, the valve stem threads are in direct contact with the medium, making them susceptible to erosion and unable to be lubricated. This type of structure is used in applications with small diameters and low temperatures. 　　Globe valves have the following advantages: 1. 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 a large amount of force is required to open and close them. 　　2. Not suitable for media containing particles, with high viscosity, or prone to coking. 　　3. The adjustment performance is poor. 　　According to the position of the valve stem thread, stop valves are classified 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 their sealing mechanism, globe valves are divided into globe valves with packing seals and those with diaphragm seals. 　　Structural forms of globe valves: The structural forms of the globe valve body include straight-through type, parallel flow type, and right-angled type. The straight-through type is the most common structure, but it experiences the greatest fluid resistance. DC flow has low fluid resistance and is often used for fluids containing solid particles or those with high viscosity. Right-angle valve bodies are usually forged and are suitable for globe valves with smaller diameters and higher pressures. 　　The following points should be noted regarding the installation and maintenance of 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. 　　Main standards for globe valves:
1. GB12233-89 “General valves – Iron globe valves and lift-type check valves”
2. GB12235-89 “General valves – Flanged steel globe valves and lift check valves”
3. JB/T53174-94 “Globe valves – Product quality grading”
4. JB/T53165-92 “High-pressure balanced globe valves”
5. GB/T587-93 “Marine flanged bronze globe valves”
6. GB/T590-93 “Marine flanged cast iron globe valves”
7. GB8464-87 “Gate valves, globe valves, ball valves, check valves with internal thread connections – Basic dimensions – Iron globe valves”
8. GB8465.2-87 “Gate valves, globe valves, ball valves, check valves with internal thread connections – Basic dimensions – Iron globe valves”

Brother upstairs, if you don’t understand something, don’t pretend to do so; don’t rush to copy things from the internet just for points. Let’s not cause visual fatigue either.

When a gate valve can be used, there is no need for a globe valve, as the torque required to open and close a globe valve is relatively high

　Globe valves are classified as valves with forced sealing; 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.

Gate valves are relatively expensive, but they are not prone to internal leakage; they are durable, and they are used in applications with high pressures. The nominal diameter of globe valves is small, making it relatively difficult to open and close them.

Our principle is: use globe valves for steam, and gate valves for all liquids

In one sentence: It should be used in all places where backflow needs to be prevented

In my opinion, globe valves are generally used for gases to ensure good sealing, while gate valves are used for liquids.

Look up the internal construction diagrams of their valves and you’ll know the differences between them

The most important function of a stop valve is to shut off flow. The valve core is not prone to damage. Gate valves can also be used to shut off flow, but their valve cores are prone to erosion over time, which can lead to damage.

Stop valves are generally used in pipelines with a nominal diameter of DN150 or less, and they can serve to regulate flow rate to a certain extent. Used in high-pressure applications.

Generally, globe valves can withstand high pressures