[Abstract] Valves are an important part of the pipeline system, which can not be neglected. The author of the valve principle has carried on the detailed introduction, and has put forward the corresponding suggestion, hoped that the related staff carries on the valve installment in the maintenance process according to the actual situation carries on the scientific, the reasonable choice.
Key words: valve; failure; maintenance; suggestion CLC: TH14 Document code: A Article ID: 1009-914X (2017) 19-0269-01
1. Introduction to the valve 1.1 Nominal diameter and nominal pressure Two important indicators of the valve is the nominal diameter and nominal pressure. The nominal diameter: "DN + number" said the valve diameter, but it is not the actual value of the valve diameter, according to the provisions of national standards, the measured value is greater than or equal to 95% of the nominal diameter value. General valve metric, American standard valve for the British system; and nominal pressure: it is used "PN + number" that the size of the pressure, the nominal pressure is not equal to the actual measured value of the valve, which is the valve at the reference temperature allows the maximum working pressure, the choice of Should be closer to this value.
1.2 The characteristics of the valve The characteristics of the valve is mainly manifested in the use and structure, including the use of features including the type of valve, structure, material, etc., the use of different characteristics of the valve used in the scope and performance are different; the use of structural features Mainly including the size of the valve, the connection and the structure of the valve stem, etc., different structures of the valve required maintenance and repair methods are different, which need to be selected according to the actual situation.
1.3 Performance Specifications Valve performance indicators include flow coefficient, cavitation coefficient and sealing performance of these three areas. First of all, the flow coefficient is a measure of valve flow capacity indicators, the greater the flow coefficient, the pressure loss through the valve when the medium is smaller; Second, the cavitation coefficient: measured according to the use of conditions to be obtained; Finally, the sealing performance of the valve seal media Leak size of an indicator, divided into two kinds of internal leakage and leakage. Internal leakage refers to "lax off", leakage refers to the flow from the valve outside the valve.
1.4 Casting defects Casting process for the production of valves, and sometimes inevitably have some defects, such as trachoma, porosity, porosity, slag and other hole-type defects; cold and hot-type defects; structural shape and size defects.
1.5 Production Standards Valve production is divided into two kinds of national standard and enterprise standards, valve Ming must be marked with the national standard number or enterprise-level instructions. The valve manual must be marked: specifications, working pressure, manufacturing standards, stem material, sealing material, packing material, fluid flow, manufacturer name, date of manufacture, the serial number, installation and maintenance precautions and so on.
2. Advantages and disadvantages of pipeline valves Analysis of different conditions, different environments, different media and different requirements, gave birth to various forms of various valves. Here are several commonly used valves, for example, simply analyze their advantages and disadvantages.
2.1 gate valve
Gate valve works mainly through the pressure valve, close and drain the fluid. With a small loss of fluid pressure, fluid flow is not restricted, the physical structure is simple, durable, but also has the advantages of mature manufacturing technology. But the disadvantage is bulky, bulky open higher height, large installation space, sealing surface prone to scratches, gate and stem easily fall off, high-speed flow will cause local open gate vibration conditions. For infrequent opening and closing of the piping system.
2.2 stop valve
The working principle of the stop valve is mainly the valve flap moves along the center of the valve, and the valve is opened and closed. The advantage is that high temperature, wear-resistant, manufacturing technology is better, easy maintenance. The disadvantage is the fluid pressure loss, slow opening. Only allow one-way flow of medium, the sealing is slightly worse. Scope of application: Suitable for heating and steam systems, in the pipeline system, the need to cut off the flow of the general use of globe valve.
2.3 butterfly valve
The working principle of the butterfly valve is the disc is a disc, the valve stem reciprocates within the range of 0 ° ~ 90 ° to achieve the valve opening and closing. The advantage is that the structure is simple, small size, light weight, simple operation, small fluid pressure loss. The disadvantage is that the flow adjustment range is not large, poor sealing performance, valve plate erosion by the larger media. Scope: Suitable for small space, large diameter pipe system.
3. The installation and use of the valve 3.1 Check valve installation Check valve is divided into lifting type, swing type two. DN ball valve or gate valve for easy access; for pipe sections fitted with a backflow preventer, there is no need to install a check valve.
3.2 decompression valve installation and installation of pressure reducing valve in general need to increase the bypass pipe. However, the water supply system in the partition need to add pressure relief valve, the bypass pipe must not be added, but to set up two sets of the same configuration of the pressure relief valve, one by one prepared. Pressure relief valve to be installed upright in the horizontal pipe, can not be tilted.
3.3 control valve
Sometimes in order to regulate the control fluid pressure, flow and other parameters, the need to install the adjustment mechanism (control valve), the principle is to change the valve disc and valve seat area of ​​circulation, in order to achieve the purpose of regulation, the control generally electric, pneumatic Type, hydraulic type and so on. Commonly used control valves are electric control valve , pressure reducing valve, pneumatic control valve , pressure regulator valve.
3.4 The principle of selection and use of valves Stop valve is generally used for DN ≤ 50mm water supply pipe network, air-conditioning pipe to minimize the use of globe valve. Gate valve is usually used for opening and closing often do not need, and long-term to keep the gate fully open or fully closed case. Gate valve can not be used as a regulation of flow, generally not used for transporting medium such as slurry pipeline. Gate valve in a small opening, the closing speed must be slow, otherwise it will have a water hammer. Under normal circumstances, the butterfly valve diameter 150mm worm gear (D371X, D341X). When the butterfly valve is used as regulating flow, it should not be used for a long time within the opening of 15 °, which will cause vibration and cavitation. Other features of the valve selection. ①close the valve required to close: the globe valve, plunger valve , ball valve; ② flow control valve: globe valve, plug valve , ball valve; ③ change the direction of the valve: plug valve, ball valve; ④ with suspended particles of the fluid Valve: ball valve and plug valve; ⑤ full open, fully closed the most convenient valve: ball valve, gate valve; ⑥ installation space should be used in small places of the valve: butterfly valve, ⑦ pump import and export should adopt the valve: butterfly valve; , The valve used between the water collector: differential pressure bypass valve; ⑨ directional valves: cut-off valve, throttle valve , pressure reducing valve, check valve; ⑩ variable flow valve system used in heating projects: Balance valve .
3.5 Valve Installation Water supply valve wall paint must be non-toxic, the valve for sewage engineering should be corrosion-resistant, easy to plug. The quality of the valve installation directly affects the quality of the results, if not properly installed, the valve performance may decline, it must be taken seriously.
First, the valve before installation, you must carefully read the valve manual; distinguish the direction and position of the valve.
Second, the valve hoisting, the rope should be tied in the bonnet and valve body flange connection, not tied to the hand wheel or stem.
Third, the valve and pipe counterparts connected, shall not be forced to pull hard to force counterparts. Flange bolts to diagonal fastening, and then tighten the order.
Fourth, the entire process of valve installation corner not too much.
Fifth, the valve part of the installation to ensure the stability of hemp silk, along the hemp along the paint to reduce the accumulation of rust, which will affect the safety of the use of the valve.
Sixthly, in the installation of steam-type pipe, the fixed valve bracket must be installed to set the correct location and proper installation and use rules to ensure that changes in the pipe expansion and contraction will not cause the valve to burst.
References [1] Qiu Yeqin. Analysis of valve design in the field of knowledge problems [J] Science and Technology Innovation, 2010.12: 17-19.
[2] Liu Jin. Causes of valve failures and treatment methods [J]. Technology Innovation Herald, 2011.09: 38-40.
[3] Chen Changjun, Wang Wei, Wang Haitao, Che Kwok. Common valve failures and maintenance of research [J]. Electrical and Mechanical Information, 2012.11: 33-35.
Key words: valve; failure; maintenance; suggestion CLC: TH14 Document code: A Article ID: 1009-914X (2017) 19-0269-01
1. Introduction to the valve 1.1 Nominal diameter and nominal pressure Two important indicators of the valve is the nominal diameter and nominal pressure. The nominal diameter: "DN + number" said the valve diameter, but it is not the actual value of the valve diameter, according to the provisions of national standards, the measured value is greater than or equal to 95% of the nominal diameter value. General valve metric, American standard valve for the British system; and nominal pressure: it is used "PN + number" that the size of the pressure, the nominal pressure is not equal to the actual measured value of the valve, which is the valve at the reference temperature allows the maximum working pressure, the choice of Should be closer to this value.
1.2 The characteristics of the valve The characteristics of the valve is mainly manifested in the use and structure, including the use of features including the type of valve, structure, material, etc., the use of different characteristics of the valve used in the scope and performance are different; the use of structural features Mainly including the size of the valve, the connection and the structure of the valve stem, etc., different structures of the valve required maintenance and repair methods are different, which need to be selected according to the actual situation.
1.3 Performance Specifications Valve performance indicators include flow coefficient, cavitation coefficient and sealing performance of these three areas. First of all, the flow coefficient is a measure of valve flow capacity indicators, the greater the flow coefficient, the pressure loss through the valve when the medium is smaller; Second, the cavitation coefficient: measured according to the use of conditions to be obtained; Finally, the sealing performance of the valve seal media Leak size of an indicator, divided into two kinds of internal leakage and leakage. Internal leakage refers to "lax off", leakage refers to the flow from the valve outside the valve.
1.4 Casting defects Casting process for the production of valves, and sometimes inevitably have some defects, such as trachoma, porosity, porosity, slag and other hole-type defects; cold and hot-type defects; structural shape and size defects.
1.5 Production Standards Valve production is divided into two kinds of national standard and enterprise standards, valve Ming must be marked with the national standard number or enterprise-level instructions. The valve manual must be marked: specifications, working pressure, manufacturing standards, stem material, sealing material, packing material, fluid flow, manufacturer name, date of manufacture, the serial number, installation and maintenance precautions and so on.
2. Advantages and disadvantages of pipeline valves Analysis of different conditions, different environments, different media and different requirements, gave birth to various forms of various valves. Here are several commonly used valves, for example, simply analyze their advantages and disadvantages.
2.1 gate valve
Gate valve works mainly through the pressure valve, close and drain the fluid. With a small loss of fluid pressure, fluid flow is not restricted, the physical structure is simple, durable, but also has the advantages of mature manufacturing technology. But the disadvantage is bulky, bulky open higher height, large installation space, sealing surface prone to scratches, gate and stem easily fall off, high-speed flow will cause local open gate vibration conditions. For infrequent opening and closing of the piping system.
2.2 stop valve
The working principle of the stop valve is mainly the valve flap moves along the center of the valve, and the valve is opened and closed. The advantage is that high temperature, wear-resistant, manufacturing technology is better, easy maintenance. The disadvantage is the fluid pressure loss, slow opening. Only allow one-way flow of medium, the sealing is slightly worse. Scope of application: Suitable for heating and steam systems, in the pipeline system, the need to cut off the flow of the general use of globe valve.
2.3 butterfly valve
The working principle of the butterfly valve is the disc is a disc, the valve stem reciprocates within the range of 0 ° ~ 90 ° to achieve the valve opening and closing. The advantage is that the structure is simple, small size, light weight, simple operation, small fluid pressure loss. The disadvantage is that the flow adjustment range is not large, poor sealing performance, valve plate erosion by the larger media. Scope: Suitable for small space, large diameter pipe system.
3. The installation and use of the valve 3.1 Check valve installation Check valve is divided into lifting type, swing type two. DN ball valve or gate valve for easy access; for pipe sections fitted with a backflow preventer, there is no need to install a check valve.
3.2 decompression valve installation and installation of pressure reducing valve in general need to increase the bypass pipe. However, the water supply system in the partition need to add pressure relief valve, the bypass pipe must not be added, but to set up two sets of the same configuration of the pressure relief valve, one by one prepared. Pressure relief valve to be installed upright in the horizontal pipe, can not be tilted.
3.3 control valve
Sometimes in order to regulate the control fluid pressure, flow and other parameters, the need to install the adjustment mechanism (control valve), the principle is to change the valve disc and valve seat area of ​​circulation, in order to achieve the purpose of regulation, the control generally electric, pneumatic Type, hydraulic type and so on. Commonly used control valves are electric control valve , pressure reducing valve, pneumatic control valve , pressure regulator valve.
3.4 The principle of selection and use of valves Stop valve is generally used for DN ≤ 50mm water supply pipe network, air-conditioning pipe to minimize the use of globe valve. Gate valve is usually used for opening and closing often do not need, and long-term to keep the gate fully open or fully closed case. Gate valve can not be used as a regulation of flow, generally not used for transporting medium such as slurry pipeline. Gate valve in a small opening, the closing speed must be slow, otherwise it will have a water hammer. Under normal circumstances, the butterfly valve diameter 150mm worm gear (D371X, D341X). When the butterfly valve is used as regulating flow, it should not be used for a long time within the opening of 15 °, which will cause vibration and cavitation. Other features of the valve selection. ①close the valve required to close: the globe valve, plunger valve , ball valve; ② flow control valve: globe valve, plug valve , ball valve; ③ change the direction of the valve: plug valve, ball valve; ④ with suspended particles of the fluid Valve: ball valve and plug valve; ⑤ full open, fully closed the most convenient valve: ball valve, gate valve; ⑥ installation space should be used in small places of the valve: butterfly valve, ⑦ pump import and export should adopt the valve: butterfly valve; , The valve used between the water collector: differential pressure bypass valve; ⑨ directional valves: cut-off valve, throttle valve , pressure reducing valve, check valve; ⑩ variable flow valve system used in heating projects: Balance valve .
3.5 Valve Installation Water supply valve wall paint must be non-toxic, the valve for sewage engineering should be corrosion-resistant, easy to plug. The quality of the valve installation directly affects the quality of the results, if not properly installed, the valve performance may decline, it must be taken seriously.
First, the valve before installation, you must carefully read the valve manual; distinguish the direction and position of the valve.
Second, the valve hoisting, the rope should be tied in the bonnet and valve body flange connection, not tied to the hand wheel or stem.
Third, the valve and pipe counterparts connected, shall not be forced to pull hard to force counterparts. Flange bolts to diagonal fastening, and then tighten the order.
Fourth, the entire process of valve installation corner not too much.
Fifth, the valve part of the installation to ensure the stability of hemp silk, along the hemp along the paint to reduce the accumulation of rust, which will affect the safety of the use of the valve.
Sixthly, in the installation of steam-type pipe, the fixed valve bracket must be installed to set the correct location and proper installation and use rules to ensure that changes in the pipe expansion and contraction will not cause the valve to burst.
References [1] Qiu Yeqin. Analysis of valve design in the field of knowledge problems [J] Science and Technology Innovation, 2010.12: 17-19.
[2] Liu Jin. Causes of valve failures and treatment methods [J]. Technology Innovation Herald, 2011.09: 38-40.
[3] Chen Changjun, Wang Wei, Wang Haitao, Che Kwok. Common valve failures and maintenance of research [J]. Electrical and Mechanical Information, 2012.11: 33-35.
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