Problem description:
Is globe valve a general term for gate valve and butterfly valve?
What is the sign of difference?
What's the use?
Analysis:
As far as I know, global valves and ball valves refer to ball valves. There is a saying that "Global valve" should be written as "Globe valve".
It's hard to say whether globe valve is a general term for gate valve and butterfly valve. It depends entirely on how terms are defined, because these terms are all common names now, and there are no strict definitions and standards.
■■■■■ A saying:
Discussion on valve classification method
At present, due to the different classification methods of valves, there are many names of valves. This brings a lot of inconvenience to the theoretical research, scientific research and development, basic teaching, naming standards and operation of valves, resulting in conceptual confusion. For example, there are regulations in foreign countries to divide valves into 8 categories. Namely, ball valve, butterfly valve, gate valve, globe valve, pinch valve, poppet valve (including safety valve or lifting check valve), plug valve and swing check valve. This is because of the problem of classification method, which leads to conceptual confusion. For example, the stop valve is named after the function or use of the valve itself. In this sense, ball valves, butterfly valves, gate valves, pinch valve and plug valves also have such functions and functions. So, can these valves also be called globe valves? The name of poppet valve comes from the opening and closing way of valve opening and closing parts (or disc), and the opening and closing parts of gate valves and globe valves are also opened and closed in a lifting way. Can it also be called a poppet valve?
Domestic valve classification also has the above problems. For example, the general classification divides valves into eleven or twelve types, namely gate valves, globe valves, plug valves, ball valves, butterfly valves, diaphragm valves, check valves, throttle valves, safety valves, steam traps and regulating valves. This classification method takes into account the principle, function, structure and other factors, but it also causes the problem of unclear concept. Because:
From the functional analysis, gate valves, globe valves, plug valves, ball valves and butterfly valves can also be used as throttle valves, and butterfly valves, ball valves and globe valves can also be used as regulating valves. From the structural analysis, diaphragm valve can also be used as safety valve and pressure reducing valve. Theoretically, both plug valves and ball valves are valves whose opening and closing parts rotate around a fixed shaft, but the rotating bodies of the opening and closing parts have different shapes, such as conical, cylindrical and spherical.
■■■■■ Another way of saying (with definitions and characteristics of several valves attached):
Valves are widely used and classified in many ways. According to the different purposes of the valve, it can be divided into:
1. opening and closing function: used to connect or cut off pipeline media, such as globe valves, gate valves, ball valves and butterfly valves.
2. Non-return purpose: used to prevent medium from flowing back, such as check valve.
3. Adjustment: used to adjust the pressure and flow of medium, such as regulating valve and reducing valve.
4. Distribution: used to change the flow direction of medium and distribute medium, such as three-way cock, distribution valve and slide valve.
5. Safety valve: When the medium pressure exceeds the specified value, it is used to discharge excess medium to ensure the safety of pipeline system and equipment, such as safety valve and accident valve.
6. His special uses: such as steam traps, exhaust valves, sewage valves, etc.
Introduction of stop valve
The opening and closing part of the globe valve is a plug-shaped disc, the sealing surface is flat or conical, and the disc moves linearly along the fluid center line. The movement forms of the valve stem are lifting rod type (the valve stem moves up and down, and the handwheel does not move up and down) and lifting rotary rod type (the handwheel rotates up and down with the valve stem, and the nut is installed on the valve body). Globe valves are only suitable for full opening and full closing, and adjustment and throttling are not allowed.
Globe valve is a kind of forced sealing valve, so when the valve is closed, pressure must be exerted on the disc to force the sealing surface not to leak. When the medium enters the valve 6 from below the disc, the resistance to be overcome by the operating force is the friction between the valve stem and the packing and the thrust generated by the pressure of the medium. The force to close the valve is greater than the force to open the valve, so the diameter of the valve stem should be larger, otherwise the valve stem will bend. In recent years, since the appearance of self-sealing valve, the medium flow direction of stop valve has turned from above the disc to the valve cavity. At this time, under the action of medium pressure, the force to close the valve is small, while the force to open the valve is large, and the diameter of the valve stem can be reduced accordingly. At the same time, under the action of medium, this valve is also sealed. China's valve "three for one" has stipulated that the flow direction of cut-off valve is from top to bottom.
When the stop valve is opened, when the opening height of the disc is 25% ~ 30% of the nominal diameter, the flow rate has reached the maximum, indicating that the valve has reached the full open position. Therefore, the full open position of the stop valve should be determined by the stroke of the disc.
Globe valves have the following advantages:
Simple structure and convenient manufacture and maintenance.
Short working stroke and short opening and closing time.
Good sealing performance, small friction between sealing surfaces and long service life.
The disadvantages of globe valves are as follows:
The fluid resistance is large, and the force required for opening and closing is large.
Not suitable for media with particles, high viscosity and easy coking.
Poor regulation performance.
According to the position of valve stem thread, the types of globe valves are divided into external thread type and internal thread type. According to the flow direction of the medium, there are straight-through, direct-flow and angular. Globe valves are divided into sealing forms, including packing sealing globe valves and bellows sealing globe valves.
The installation and maintenance of stop valve should pay attention to the following matters:
Hand wheel and handle operated globe valves can be installed anywhere in the pipeline.
Handwheels, handles and actuators are not allowed to be used for lifting.
The flow direction of the medium should be consistent with the direction of the arrow shown on the valve body.
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Introduction of gate valve
The opening and closing part of the gate valve is the gate, and the movement direction of the gate valve is perpendicular to the direction of the fluid. Gate valves can only be fully opened and closed, and cannot be adjusted or throttled. The gate has two sealing surfaces, and the two sealing surfaces of the most commonly used mode gate valve form a wedge shape. The wedge angle varies with the valve parameters, usually 50, and 2 52' when the medium temperature is not high. The gate of wedge gate valve can be made into a whole, called rigid gate; It can also be made into a ram that can produce a small amount of deformation to improve its manufacturability and make up for the deviation of sealing surface angle during machining. This kind of hammer is called elastic hammer.
When the gate valve is closed, the sealing surface can only be sealed by medium pressure, that is, the sealing surface of the gate is pressed on the valve seat on the other side by medium pressure to ensure the sealing surface, which is self-sealing. Most gate valves are forced to seal, that is, when the valve is closed, the gate is forced to press against the valve seat by external force to ensure the tightness of the sealing surface.
The gate of the gate valve moves linearly with the valve stem, which is called lifting rod gate valve (also called lifting rod gate valve). Usually, there are trapezoidal threads on the lifting rod. Through the nut at the top of the valve and the guide groove on the valve body, the rotary motion is changed into linear motion, that is, the operating torque is changed into operating thrust.
When the valve is open, when the lifting height of the gate is equal to 1: 1 times the diameter of the valve, the fluid channel is completely unblocked, but the position cannot be monitored during operation. In actual use, the valve stem vertex is marked, that is, the position that cannot be opened is taken as its full open position. In order to consider the locking phenomenon caused by temperature change, it is usually the position where the valve is fully opened after opening to the top position, and then it goes back to 1/2- 1. Therefore, the fully open position of the valve is determined according to the position (i.e. stroke) of the gate.
In some gate valves, the stem nut is arranged on the gate, and the rotation of the handwheel drives the stem to rotate, so that the gate can be lifted. This valve is called rotary stem gate valve or hidden stem gate valve.
Gate valves have the following advantages:
The fluid resistance is small, and the sealing surface is corroded by the medium.
Opening and closing is labor-saving.
The flow direction of the medium is unrestricted, the flow is not disturbed, and the pressure is not reduced.
Simple shape, short structural length, good manufacturing technology and wide application range.
The disadvantages of gate valves are as follows:
It is easy to cause erosion wear between sealing surfaces and difficult to maintain.
The overall size is large, it needs a certain space to open, and the opening and closing time is long.
The structure is more complicated.
The types of gate width can be divided into wedge gate valves and parallel gate valves according to the configuration of sealing surfaces, and wedge gate valves can be divided into single gate valves, double gate plates and elastic gate valves. Parallel gate valves can be divided into single gate type and double gate type. According to the thread position of the valve stem, it can be divided into two types: open stem gate valve and hidden stem gate valve.
The installation and maintenance of gate valves should pay attention to the following matters:
Handwheel, handle and transmission mechanism are not allowed to be lifted, and collision is strictly prohibited.
Double-gate gate valves should be installed vertically (i.e. the valve stem is in the vertical position and the handwheel is at the top).
The gate valve with bypass valve should open the bypass valve before opening (to balance the pressure difference between the inlet and outlet and reduce the opening force).
The gate valve with transmission mechanism shall be installed as specified in the product manual.
If the valve is frequently opened and closed, lubricate it at least once a month.
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Brief introduction of butterfly valve
Butterfly valve is a disc-shaped butterfly plate, which rotates around its own axis in the valve body to realize opening, closing or adjustment. The butterfly valve is usually less than 90 degrees from full opening to full closing, and the butterfly valve and the butterfly valve stem are not self-locking. In order to locate the butterfly plate, a worm gear reducer should be installed on the valve stem. Using worm gear reducer can not only make the butterfly plate have self-locking ability, make the butterfly plate stop at any position, but also improve the working performance of the valve.
Industrial butterfly valve has the characteristics of high temperature resistance, wide applicable pressure range, large nominal diameter, carbon steel valve body and valve plate using metal ring instead of rubber ring. Large-scale high-temperature butterfly valve is welded by steel plate, which is mainly used for flue gas pipeline of high-temperature medium.
The advantages of butterfly valves are as follows:
Convenient and quick opening and closing, labor-saving, low fluid resistance and frequent operation.
Simple structure, small volume and light weight.
Mud can be transported, and the liquid accumulated at the nozzle is the least.
Good sealing can be achieved at low pressure.
Good regulation performance.
The disadvantages of butterfly valves are as follows:
The range of use pressure and working temperature is small.
Poor sealing.
Butterfly valves can be divided into offset, vertical, inclined plate and lever type according to their structural forms. According to the sealing form, it can be divided into two types: relative sealing type and hard sealing type. Soft seal type generally adopts rubber ring seal, and hard seal type generally adopts metal ring seal.
According to the connection type, it can be divided into flange connection and clamp connection; According to the transmission mode, it can be divided into manual, gear transmission, pneumatic, hydraulic and electric.
The installation and maintenance of butterfly valves should pay attention to the following matters:
During installation, the disc should stop in the closed position.
The opening position should be determined by the rotation angle of the butterfly plate.
Butterfly valves with bypass valves should be opened before opening.
The installation shall be carried out according to the manufacturer's installation instructions, and the heavy butterfly valve shall be provided with a solid foundation.
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Introduction of ball valve
Ball valve is a kind of valve which uses a ball with a circular passage as the opening and closing part, and the ball rotates with the valve stem to realize the opening and closing action. The opening and closing part of the ball valve is a sphere with a hole, which rotates around the axis perpendicular to the channel, thus achieving the purpose of opening and closing the channel. Ball valves are mainly used to open and close pipelines and equipment media.
The main advantages of ball valves are as follows:
Suitable for frequent operation, quick and light opening and closing.
Fluid resistance is small.
Simple structure, small relative volume, light weight and easy maintenance.
Good sealing performance
Not limited by the installation direction, the flow direction of the medium can be arbitrary.
No vibration, low noise.
The main disadvantages of ball valves are as follows:
Ball valves can be divided into floating ball valves, fixed ball valves, elastic ball valves and oil-sealed ball valves according to their structural forms; According to the channel, it can be divided into straight energy type, angle type and three-way type, and the three-way type can be divided into two types: T type and L type. According to the connection mode, it can be divided into three types: threaded connection, flange connection and welding.
Ball valve installation and maintenance should pay attention to the following matters:
Leave the position where the valve handle rotates.
Can't be used for throttling.
Ball valve with transmission mechanism should be installed vertically.