Use and classification of valves

Use and classification of valves
Shijiazhuang Jingjin Mechanical Equipment Installation Co., Ltd. --- Zhou Yanhui
(1) Shutdown class. This type of valve is only used to cut off or connect fluid, such as stop valve, gate valve, ball valve, etc.
(2) Regulation. This type of valve is used to regulate the flow or pressure of fluid, such as regulating valve, pressure reducing valve and throttle valve.
(3) Protection category. This type of valve is used for some protection, such as safety valve, check valve and quick closing valve.
Valves can be divided into:
(1) Low pressure valve, Pg ≤ 1.6MPa (16kg/cm2);
(2) Medium pressure valve, Pg=2.5~6.4 MPa (25~64 kg/cm2);
(3) High pressure valve, Pg=10~80MPa (100~800kg/cm2);
(4) Ultra high pressure valve, Pg ≥ 100 MPa (1000 kg/cm2);
(5) Vacuum valve, Pg is lower than atmospheric pressure.
The valves can be divided into: low temperature valve: t ＜ - 30 ℃ according to the working temperature; Medium temperature valve: 120 ℃≤ t ≤ 450 ℃; High temperature valve: t ＞ 450 ℃; Normal temperature valve: - 30 ℃ ≤ t ＜ 120 ℃.
The valve can be divided into manual valve, electric valve, pneumatic valve, hydraulic valve, etc. according to the driving mode.
The valves commonly used in the chemical system of the power plant mainly include: butterfly valve (including manual butterfly valve, pneumatic butterfly valve and electric butterfly valve), rubber lined diaphragm valve (manual and pneumatic), stop valve, gate valve, ball valve, check valve, pressure reducing valve, safety valve, etc.
1、 Butterfly valve
The butterfly valve is a valve that uses a round butterfly plate rotating with the valve stem as the opening and closing part to realize the opening and closing action. The butterfly valve is mainly used as a block valve, and can also be designed to have the function of adjustment or both. The butterfly valve is mainly used on low-pressure large and medium diameter pipelines.
Main advantages of butterfly valve:
(1) With simple structure, short length, small volume and light weight, the weight can be reduced by half compared with the gate valve, especially the advantages of the wafer butterfly valve.
(2) The fluid resistance is small. The butterfly valve with medium and large diameter has a large effective flow area when it is fully opened.
(3) The opening and closing are convenient, fast and labor-saving. The butterfly valve can be opened and closed by rotating 90 °. Since the force acting on the butterfly plates at both sides of the shaft by the medium is nearly equal, the torque direction generated is opposite, so the opening and closing torque is small.
(4) Good sealing at low pressure. Most butterfly valves use rubber sealing rings, so the sealing performance is good.
(5) The adjustment performance is good. The flow of medium can be better controlled by changing the rotation angle of the butterfly plate.
Main disadvantages of butterfly valves: limited by sealing ring materials, the range of operating pressure and temperature of butterfly valves is small. Most butterfly valves use rubber sealing rings, and the operating temperature is limited by rubber materials. With the development of sealing materials and metal sealing butterfly valves, the range of operating temperature and operating pressure of butterfly valves has been expanded.
2、 Gate valve
Gate valve is also called gate valve. It relies on the high smoothness, flatness and consistency of the sealing surface of the gate to prevent the medium from flowing, and on the top wedge to increase the sealing effect. The closing member moves up and down in a straight line along the vertical direction of the center line of the valve seat to connect or cut off the medium in the pipeline.
Main advantages of gate valve:
(1) The fluid resistance is small. The medium channel inside the gate valve body is straight through, and the medium does not change the flow direction when flowing through the gate valve, so the flow resistance is small.
(2) It is easier to open and close. When opening and closing, the ram movement direction is perpendicular to the medium flow direction. Compared with the globe valve, the opening and closing of the gate valve is labor-saving.
(3) The medium flow direction is generally unrestricted. The medium can flow through both sides of the gate valve in any direction to achieve the purpose of connection or cutoff.
(4) It is easy to install and applicable to the pipeline where the flow direction of the medium may change.
Main disadvantages of gate valve:
(1) The height is large and the opening and closing time is long. Because it is necessary to lift the gate completely above the valve seat channel when opening, and it is necessary to lower all the gates to block the valve seat channel when closing, the opening and closing travel of the gate is large, the lifting height is correspondingly increased, and the opening and closing time is long.
(2) The sealing surface is easy to scratch. When opening and closing, there is relative sliding between the two sealing surfaces contacting the gate and the valve seat, which is easy to cause scratches under the action of the medium, thus damaging the sealing performance and affecting the service life.
3、 Diaphragm valve
Diaphragm valve is a special type of block valve. The main difference between its internal structure and other valves is that it has no stuffing box. Its opening and closing parts are a diaphragm made of materials with high strength or wear resistance, which separates the inner cavity of the valve body from the inner cavity of the valve cover, thus eliminating the hidden danger of leakage caused by the erosion of the drive parts of the valve by media. Diaphragm valves are mainly used for equipment and pipeline systems containing hard suspended solids, corrosive media and high sealing requirements.
Features of diaphragm valve:
(1) The inner cavity of the lower valve body is separated from the inner cavity of the upper valve body by the diaphragm, so that the valve stem, valve clack and other parts above the diaphragm are not corroded by the medium, and the medium leakage will not occur, thus eliminating the stuffing box sealing structure.
(2) The diaphragm is made of soft sealing materials such as rubber or plastic, with good sealing performance. As the diaphragm is a vulnerable part, it should be replaced regularly according to the working conditions and medium characteristics.
(3) Limited by diaphragm material, diaphragm valve is applicable to equipment and pipelines with low pressure (PN ≤ 1.6MPa) and low temperature (t ≤ 190 ℃).
(4) It has good anti-corrosion characteristics.
4、 Stop valve
The stop valve is a commonly used block valve, which is mainly used to connect or cut off the medium in the pipeline. It is generally used for medium and small caliber pipelines, and is applicable to a wide range of pressures and temperatures. The stop valve is generally not used to regulate the medium flow. The structural forms of stop valve body include straight through type, direct flow type and angle type. The straight through type is the most common structure, but its fluid resistance is the largest; The flow resistance of the direct flow type is small, and it is mostly used for the fluid containing solid particles or with high viscosity; The angle valve body is usually forged, which is suitable for pipes with smaller diameter and higher pressure.
Main advantages of stop valve:
(1) The structure of the stop valve is relatively simple, and the manufacturing and maintenance are relatively convenient;
(2) The sealing surface is not easy to wear and scratch, with good sealing performance and long service life;
(3) When opening and closing, the valve disc travel is small, the opening and closing time is short, and the valve height is small.
Main disadvantages of stop valve:
(1) The fluid resistance is large, and the medium channel in the valve body is relatively tortuous, so the energy consumption is large.
(2) The opening and closing torque is large and the opening and closing are laborious. When closing, because the movement direction of the valve clack is opposite to the action direction of the medium pressure, the movement of the valve clack must overcome the force of the medium, so the opening and closing torque is large.
(3) The flow direction of the medium is generally limited by the requirement of flowing from bottom to top.
5、 Check valve
The check valve is a valve that can automatically prevent the flow back, also known as a check valve. The valve clack of the check valve is opened under the fluid pressure, and the fluid flows from the inlet side to the outlet side. When the pressure at the inlet side is lower than that at the outlet side, the valve clack automatically closes under the effect of factors such as fluid differential pressure and its own gravity to prevent fluid backflow. A check valve is usually used at the pump outlet.
Check valves are generally divided into lift type, swing type, butterfly type and diaphragm type. The structure of the lift check valve is generally similar to that of the globe valve. Its flap moves up and down along the centerline of the channel with reliable action, but the fluid resistance is large, and it is suitable for smaller caliber applications. The flap of swing check valve rotates around the rotating shaft, and its fluid resistance is generally less than that of lift check valve. It is suitable for large caliber applications. The disc of butterfly check valve is similar to butterfly valve, with simple structure, small flow resistance and low water hammer pressure. Diaphragm check valves have a variety of structural forms, all of which use diaphragm as the opening and closing part. Due to its good performance of waterproof hammer, simple structure and low cost, it has developed rapidly in recent years. However, the operating temperature and pressure of the diaphragm check valve are limited by the diaphragm material.
6、 Ball valve
Ball valve is a valve that uses a ball with a circular through hole as the opening and closing part, and the ball rotates with the valve stem to realize the opening and closing action. The main function of the ball valve is to cut off and connect the medium flow channel in the pipeline. Its working principle is to rotate the ball by 90 ° with the help of the handle or other driving devices, so that the through hole of the ball coincides with or is vertical to the centerline of the valve body channel, so as to complete the full opening or closing of the valve.
Advantages of ball valve:
(1) The fluid resistance is small. When the ball channel, valve body channel and connecting pipe are fully opened, their sectional areas are equal, and they are connected in a straight line. The medium flows through the ball valve, which is equivalent to flowing through a section of straight pipe. The valves through which the resin passes in the chemical water system are generally ball valves.
(2) It can be opened and closed quickly. When opening and closing, you only need to turn the ball 90 °, which is convenient and fast.
(3) Simple structure, small volume and light weight. In particular, its height is far less than that of gate valve and globe valve.
(4) Good sealing performance. Ball valves generally use flexible soft sealing rings.
Disadvantages of ball valve: small temperature range. The ball valve generally adopts soft sealing ring, and the service temperature is limited by the sealing ring material.
7、 Pressure reducing valve
The function of the pressure reducing valve is to reduce the pressure of the medium in the pipeline of the equipment to the required pressure. It relies on its sensing elements (diaphragm, spring, etc.) to change the position of the valve disc, increase the local resistance of the pipeline, and thus reduce the pressure of the medium.
8、 Safety valve
The safety valve is an automatic protection device for equipment and pipelines. In chemical water treatment equipment and pipelines, it is often used on pressure vessels such as steam pipelines, heaters, compressed air pipelines and gas storage tanks. When the medium pressure exceeds the specified value, the safety valve automatically opens to eliminate the excess medium pressure; When the pressure drops to the reseating pressure, it can be automatically closed to ensure the safety of production and operation.
Safety valves can be divided into straight through safety valves and pulse safety valves according to their structures. Straight through safety valves can also be divided into lever hammer safety valves and spring safety valves. Spring type safety valve is commonly used in chemical water system. Action principle of spring type safety valve: during normal operation, the downward force of the spring is greater than the upward force of the fluid on the valve core, and the safety valve is closed. Once the fluid pressure exceeds the allowable pressure, the upward force of the fluid acting on the door core increases, the door core is jacked open, and the fluid overflows. When the fluid pressure drops below the spring force, the spring presses the door core to force it to close.

(1) Shutdown class. This type of valve is only used to cut off or connect fluid, such as stop valve, gate valve, ball valve, etc.
(2) Regulation. This type of valve is used to regulate the flow or pressure of fluid, such as regulating valve, pressure reducing valve and throttle valve.
(3) Protection category. This type of valve is used for some protection, such as safety valve, check valve and quick closing valve.
Valves can be divided into:
(1) Low pressure valve, Pg ≤ 1.6MPa (16kg/cm2);
(2) Medium pressure valve, Pg=2.5~6.4 MPa (25~64 kg/cm2);
(3) High pressure valve, Pg=10~80MPa (100~800kg/cm2);
(4) Ultra high pressure valve, Pg ≥ 100 MPa (1000 kg/cm2);
(5) Vacuum valve, Pg is lower than atmospheric pressure.
The valves can be divided into: low temperature valve: t ＜ - 30 ℃ according to the working temperature; Medium temperature valve: 120 ℃≤ t ≤ 450 ℃; High temperature valve: t ＞ 450 ℃; Normal temperature valve: - 30 ℃ ≤ t ＜ 120 ℃.
The valve can be divided into manual valve, electric valve, pneumatic valve, hydraulic valve, etc. according to the driving mode.
The valves commonly used in the chemical system of the power plant mainly include: butterfly valve (including manual butterfly valve, pneumatic butterfly valve and electric butterfly valve), rubber lined diaphragm valve (manual and pneumatic), stop valve, gate valve, ball valve, check valve, pressure reducing valve, safety valve, etc.
1、 Butterfly valve
The butterfly valve is a valve that uses a round butterfly plate rotating with the valve stem as the opening and closing part to realize the opening and closing action. The butterfly valve is mainly used as a block valve, and can also be designed to have the function of adjustment or both. The butterfly valve is mainly used on low-pressure large and medium diameter pipelines.
Main advantages of butterfly valve:
(1) With simple structure, short length, small volume and light weight, the weight can be reduced by half compared with the gate valve, especially the advantages of the wafer butterfly valve.
(2) The fluid resistance is small. The butterfly valve with medium and large diameter has a large effective flow area when it is fully opened.
(3) The opening and closing are convenient, fast and labor-saving. The butterfly valve can be opened and closed by rotating 90 °. Since the force acting on the butterfly plates at both sides of the shaft by the medium is nearly equal, the torque direction generated is opposite, so the opening and closing torque is small.
(4) Good sealing at low pressure. Most butterfly valves use rubber sealing rings, so the sealing performance is good.
(5) The adjustment performance is good. The flow of medium can be better controlled by changing the rotation angle of the butterfly plate.
Main disadvantages of butterfly valves: limited by sealing ring materials, the range of operating pressure and temperature of butterfly valves is small. Most butterfly valves use rubber sealing rings, and the operating temperature is limited by rubber materials. With the development of sealing materials and metal sealing butterfly valves, the range of operating temperature and operating pressure of butterfly valves has been expanded.
2、 Gate valve
Gate valve is also called gate valve. It relies on the high smoothness, flatness and consistency of the sealing surface of the gate to prevent the medium from flowing, and on the top wedge to increase the sealing effect. The closing member moves up and down in a straight line along the vertical direction of the center line of the valve seat to connect or cut off the medium in the pipeline.
Main advantages of gate valve:
(1) The fluid resistance is small. The medium channel inside the gate valve body is straight through, and the medium does not change the flow direction when flowing through the gate valve, so the flow resistance is small.
(2) It is easier to open and close. When opening and closing, the ram movement direction is perpendicular to the medium flow direction. Compared with the globe valve, the opening and closing of the gate valve is labor-saving.
(3) The medium flow direction is generally unrestricted. The medium can flow through both sides of the gate valve in any direction to achieve the purpose of connection or cutoff.
(4) It is easy to install and applicable to the pipeline where the flow direction of the medium may change.
Main disadvantages of gate valve:
(1) The height is large and the opening and closing time is long. Because it is necessary to lift the gate completely above the valve seat channel when opening, and it is necessary to lower all the gates to block the valve seat channel when closing, the opening and closing travel of the gate is large, the lifting height is correspondingly increased, and the opening and closing time is long.
(2) The sealing surface is easy to scratch. When opening and closing, there is relative sliding between the two sealing surfaces contacting the gate and the valve seat, which is easy to cause scratches under the action of the medium, thus damaging the sealing performance and affecting the service life.
3、 Diaphragm valve
Diaphragm valve is a special type of block valve. The main difference between its internal structure and other valves is that it has no stuffing box. Its opening and closing parts are a diaphragm made of materials with high strength or wear resistance, which separates the inner cavity of the valve body from the inner cavity of the valve cover, thus eliminating the hidden danger of leakage caused by the erosion of the drive parts of the valve by media. Diaphragm valves are mainly used for equipment and pipeline systems containing hard suspended solids, corrosive media and high sealing requirements.
Features of diaphragm valve:
(1) The inner cavity of the lower valve body is separated from the inner cavity of the upper valve body by the diaphragm, so that the valve stem, valve clack and other parts above the diaphragm are not corroded by the medium, and the medium leakage will not occur, thus eliminating the stuffing box sealing structure.
(2) The diaphragm is made of soft sealing materials such as rubber or plastic, with good sealing performance. As the diaphragm is a vulnerable part, it should be replaced regularly according to the working conditions and medium characteristics.
(3) Limited by diaphragm material, diaphragm valve is applicable to equipment and pipelines with low pressure (PN ≤ 1.6MPa) and low temperature (t ≤ 190 ℃).

(4) It has good anti-corrosion characteristics.

4、 Stop valve
The stop valve is a commonly used block valve, which is mainly used to connect or cut off the medium in the pipeline. It is generally used for medium and small caliber pipelines, and is applicable to a wide range of pressures and temperatures. The stop valve is generally not used to regulate the medium flow. The structural forms of stop valve body include straight through type, direct flow type and angle type. The straight through type is the most common structure, but its fluid resistance is the largest; The flow resistance of the direct flow type is small, and it is mostly used for the fluid containing solid particles or with high viscosity; The angle valve body is usually forged, which is suitable for pipes with smaller diameter and higher pressure.
Main advantages of stop valve:
(1) The structure of the stop valve is relatively simple, and the manufacturing and maintenance are relatively convenient;
(2) The sealing surface is not easy to wear and scratch, with good sealing performance and long service life;
(3) When opening and closing, the valve disc travel is small, the opening and closing time is short, and the valve height is small.
Main disadvantages of stop valve:
(1) The fluid resistance is large, and the medium channel in the valve body is relatively tortuous, so the energy consumption is large.
(2) The opening and closing torque is large and the opening and closing are laborious. When closing, because the movement direction of the valve clack is opposite to the action direction of the medium pressure, the movement of the valve clack must overcome the force of the medium, so the opening and closing torque is large.
(3) The flow direction of the medium is generally limited by the requirement of flowing from bottom to top.
5、 Check valve
The check valve is a valve that can automatically prevent the flow back, also known as a check valve. The valve clack of the check valve is opened under the fluid pressure, and the fluid flows from the inlet side to the outlet side. When the pressure at the inlet side is lower than that at the outlet side, the valve clack automatically closes under the effect of factors such as fluid differential pressure and its own gravity to prevent fluid backflow. A check valve is usually used at the pump outlet.
Check valves are generally divided into lift type, swing type, butterfly type and diaphragm type. The structure of the lift check valve is generally similar to that of the globe valve. Its flap moves up and down along the centerline of the channel with reliable action, but the fluid resistance is large, and it is suitable for smaller caliber applications. The flap of swing check valve rotates around the rotating shaft, and its fluid resistance is generally less than that of lift check valve. It is suitable for large caliber applications. The disc of butterfly check valve is similar to butterfly valve, with simple structure, small flow resistance and low water hammer pressure. Diaphragm check valves have a variety of structural forms, all of which use diaphragm as the opening and closing part. Due to its good performance of waterproof hammer, simple structure and low cost, it has developed rapidly in recent years. However, the operating temperature and pressure of the diaphragm check valve are limited by the diaphragm material.
6、 Ball valve
Ball valve is a valve that uses a ball with a circular through hole as the opening and closing part, and the ball rotates with the valve stem to realize the opening and closing action. The main function of the ball valve is to cut off and connect the medium flow channel in the pipeline. Its working principle is to rotate the ball by 90 ° with the help of the handle or other driving devices, so that the through hole of the ball coincides with or is vertical to the centerline of the valve body channel, so as to complete the full opening or closing of the valve.
Advantages of ball valve:
(1) The fluid resistance is small. When the ball channel, valve body channel and connecting pipe are fully opened, their sectional areas are equal, and they are connected in a straight line. The medium flows through the ball valve, which is equivalent to flowing through a section of straight pipe. The valves through which the resin passes in the chemical water system are generally ball valves.
(2) It can be opened and closed quickly. When opening and closing, you only need to turn the ball 90 °, which is convenient and fast.
(3) Simple structure, small volume and light weight. In particular, its height is far less than that of gate valve and globe valve.
(4) Good sealing performance. Ball valves generally use flexible soft sealing rings.
Disadvantages of ball valve: small temperature range. The ball valve generally adopts soft sealing ring, and the service temperature is limited by the sealing ring material.
7、 Pressure reducing valve
The function of the pressure reducing valve is to reduce the pressure of the medium in the pipeline of the equipment to the required pressure. It relies on its sensing elements (diaphragm, spring, etc.) to change the position of the valve disc, increase the local resistance of the pipeline, and thus reduce the pressure of the medium.
8、 Safety valve
The safety valve is an automatic protection device for equipment and pipelines. In chemical water treatment equipment and pipelines, it is often used on pressure vessels such as steam pipelines, heaters, compressed air pipelines and gas storage tanks. When the medium pressure exceeds the specified value, the safety valve automatically opens to eliminate the excess medium pressure; When the pressure drops to the reseating pressure, it can be automatically closed to ensure the safety of production and operation.
Safety valves can be divided into straight through safety valves and pulse safety valves according to their structures. Straight through safety valves can also be divided into lever hammer safety valves and spring safety valves. Spring type safety valve is commonly used in chemical water system. Action principle of spring type safety valve: during normal operation, the downward force of the spring is greater than the upward force of the fluid on the valve core, and the safety valve is closed. Once the fluid pressure exceeds the allowable pressure, the upward force of the fluid acting on the door core increases, the door core is jacked open, and the fluid overflows. When the fluid pressure drops below the spring force, the spring presses the door core to force it to close.