Common Assembly Methods of Valves
It is the most basic unit for valve assembly of the whole machine, and several parts make up the components of the valve (such as bonnet and disc components, etc.). The assembly process of several parts as components is called a component assembly, and the assembly process of several parts and components as valves is called general assembly. The assembler has a great influence on the product quality. Even if the design is accurate and the parts are qualified, if the assembly is improper, the valve will not meet the specified requirements, and even leak the seal. Therefore, special care should be taken to adopt a fair assembly method to ensure the final product quality of the valve. The assembly process defined in the form of documents in production is called assembly process specification.
Common assembly methods of valves: There are three commonly used valve assembly methods, namely, complete replacement method, repair method and matching method.
1. Complete Interchange Method
When the valve is assembled by the complete interchange method, each part of the valve can be assembled without any trimming and selection, and the assembled product can meet the specified technical requirements. At this time, the valve parts should be processed completely according to the design requirements to meet the requirements of dimensional accuracy and form and position tolerance. The advantages of the complete interchange method are: assembly work is simple and economical; workers do not need a high degree of skill; the production efficiency of the assembly process is high, and it is easy to organize assembly lines and specialized production. However, absolutely speaking, the machining accuracy of parts is required to be higher when completely exchanging assembly is adopted. It is suitable for valves with absolutely simple structures, such as globe valves, check valves and ball valves, and valves with medium and small caliber.
2. Matching Method
The valve is assembled by the matching method, and the whole machine can be processed according to economic precision. When assembling, a certain size with adjustment and compensation functions is matched to achieve the specified assembly precision. The principle of the matching method is similar to that of the repairing method, but it is different in the way of changing the size of the compensation ring. The former is to change the size of the compensation ring by selecting accessories, while the latter is to change the size of the compensation ring by trimming accessories. For example, the jacking core and adjusting gasket of the control valve type wedge gate valve with double gate plates, adjusting gasket between the two bodies of split ball valves, etc. are to choose special parts as compensation parts in the dimension chain related to assembly accuracy and to achieve the required assembly accuracy by adjusting the thickness of the gasket. In order to ensure that the fixed compensation parts can be selected in different situations, it is necessary to manufacture a set of hydraulic control valve models of washers and shaft sleeve compensation parts with different thickness sizes in advance for assembly.
3. Repair Method
The valve is assembled by the repair method, and the parts can be processed according to economic precision. When assembling, repair a certain size with adjustment and compensation function to achieve the specified assembly goal. For example, for the gate and valve body of the wedge gate valve, because the processing cost to realize the interchange requirement is too high, most manufacturers adopt the repair process. That is, in the final grinding of the gate sealing surface to control the opening size, the plate should be matched with the opening size of the valve body sealing surface to achieve the ultimate sealing requirement. Although this method adds the plate matching procedure, it greatly simplifies the dimensional accuracy requirements of the previous processing procedure, and the special person in the plate matching procedure is skilled in operation. Generally speaking, it will not affect production efficiency. The assembly process of valves: valves are individually assembled on a fixed site. The assembly of parts and components of valves and general assembly are carried out in the assembly workshop, and all necessary parts and components are transported to the assembly workplace. Usually, component assembly and general assembly are carried out by many groups of workers at the same time, which not only shortens the assembly cycle, but also facilitates the application of special assembly tools, and has low requirements for workers' technical level.
Some foreign manufacturers or high-tech valves also adopt the mode of assembling suspension lines or turntables.
1. Preparation before Assembly
Before the valve is assembled, the burr formed by machining and welding residue should be removed, and the packing and gasket should be cleaned and cut.
2. Cleaning of Valve Parts
As a valve installed by the fluid pipeline, the inner cavity must be clean. Especially the valves used in nuclear power, medicine and food industries, in order to ensure the purity of the medium and avoid medium infection, the requirements for the cleanliness of the inner cavity of the valve are more stringent. Before assembly, the valve parts should be cleaned, and the chips, residual smooth oil, coolant and burrs, welding slag and other contaminants on the parts should be cleaned. The valves are usually cleaned by spraying with alkaline water or hot water (kerosene can also be used for cleaning) or by ultrasonic cleaning machines. After grinding and polishing, the parts need to be cleaned for the last time. In the final cleaning, the sealing surface is usually cleaned with gasoline, then dried with compressed air and wiped with a cloth.
3. Packing and Gasket Preparation
Graphite filler is widely used because of its corrosion resistance, good sealing performance and low friction coefficient. And the packing and gasket are used to prevent the medium from leaking through the joint surfaces of the valve stem, the valve cover and the flange. These fittings should be prepared for cutting and collecting before valve assembly.
4. Assembly of Valves
Valves are usually assembled according to the sequence and method specified in the process with the valve body as the reference part. Before assembly, parts and components should be reviewed to avoid parts that are not deburred or cleaned from entering the final assembly. During the assembly process, the parts should be handled with care to avoid bumping and scratching the processing personnel. The moving parts of the valve (such as valve stem, bearing, etc.) should be coated with industrial butter. The valve cover is bolted to the valve body. When the bolts are tightened, they should be weighed, interwoven, repeatedly and evenly. Otherwise, the joint surface of the valve body and valve cover will leak due to the uneven stress around it. The handle used for fastening should not be too long, so as to prevent the excessive pre-tightening force from affecting the bolt strength. For valves with strict requirements for preload, torque should be used to tighten bolts according to specified torque requirements. After the final assembly, the holding mechanism should be rotated to check whether the movement of the valve opening and closing parts is mobile and whether there is any jamming. The valve can be tested only after the valve cover, bracket and other parts meet the requirements of the drawings.
Common assembly methods of valves: There are three commonly used valve assembly methods, namely, complete replacement method, repair method and matching method.
1. Complete Interchange Method
When the valve is assembled by the complete interchange method, each part of the valve can be assembled without any trimming and selection, and the assembled product can meet the specified technical requirements. At this time, the valve parts should be processed completely according to the design requirements to meet the requirements of dimensional accuracy and form and position tolerance. The advantages of the complete interchange method are: assembly work is simple and economical; workers do not need a high degree of skill; the production efficiency of the assembly process is high, and it is easy to organize assembly lines and specialized production. However, absolutely speaking, the machining accuracy of parts is required to be higher when completely exchanging assembly is adopted. It is suitable for valves with absolutely simple structures, such as globe valves, check valves and ball valves, and valves with medium and small caliber.
2. Matching Method
The valve is assembled by the matching method, and the whole machine can be processed according to economic precision. When assembling, a certain size with adjustment and compensation functions is matched to achieve the specified assembly precision. The principle of the matching method is similar to that of the repairing method, but it is different in the way of changing the size of the compensation ring. The former is to change the size of the compensation ring by selecting accessories, while the latter is to change the size of the compensation ring by trimming accessories. For example, the jacking core and adjusting gasket of the control valve type wedge gate valve with double gate plates, adjusting gasket between the two bodies of split ball valves, etc. are to choose special parts as compensation parts in the dimension chain related to assembly accuracy and to achieve the required assembly accuracy by adjusting the thickness of the gasket. In order to ensure that the fixed compensation parts can be selected in different situations, it is necessary to manufacture a set of hydraulic control valve models of washers and shaft sleeve compensation parts with different thickness sizes in advance for assembly.
3. Repair Method
The valve is assembled by the repair method, and the parts can be processed according to economic precision. When assembling, repair a certain size with adjustment and compensation function to achieve the specified assembly goal. For example, for the gate and valve body of the wedge gate valve, because the processing cost to realize the interchange requirement is too high, most manufacturers adopt the repair process. That is, in the final grinding of the gate sealing surface to control the opening size, the plate should be matched with the opening size of the valve body sealing surface to achieve the ultimate sealing requirement. Although this method adds the plate matching procedure, it greatly simplifies the dimensional accuracy requirements of the previous processing procedure, and the special person in the plate matching procedure is skilled in operation. Generally speaking, it will not affect production efficiency. The assembly process of valves: valves are individually assembled on a fixed site. The assembly of parts and components of valves and general assembly are carried out in the assembly workshop, and all necessary parts and components are transported to the assembly workplace. Usually, component assembly and general assembly are carried out by many groups of workers at the same time, which not only shortens the assembly cycle, but also facilitates the application of special assembly tools, and has low requirements for workers' technical level.
Some foreign manufacturers or high-tech valves also adopt the mode of assembling suspension lines or turntables.
1. Preparation before Assembly
Before the valve is assembled, the burr formed by machining and welding residue should be removed, and the packing and gasket should be cleaned and cut.
2. Cleaning of Valve Parts
As a valve installed by the fluid pipeline, the inner cavity must be clean. Especially the valves used in nuclear power, medicine and food industries, in order to ensure the purity of the medium and avoid medium infection, the requirements for the cleanliness of the inner cavity of the valve are more stringent. Before assembly, the valve parts should be cleaned, and the chips, residual smooth oil, coolant and burrs, welding slag and other contaminants on the parts should be cleaned. The valves are usually cleaned by spraying with alkaline water or hot water (kerosene can also be used for cleaning) or by ultrasonic cleaning machines. After grinding and polishing, the parts need to be cleaned for the last time. In the final cleaning, the sealing surface is usually cleaned with gasoline, then dried with compressed air and wiped with a cloth.
3. Packing and Gasket Preparation
Graphite filler is widely used because of its corrosion resistance, good sealing performance and low friction coefficient. And the packing and gasket are used to prevent the medium from leaking through the joint surfaces of the valve stem, the valve cover and the flange. These fittings should be prepared for cutting and collecting before valve assembly.
4. Assembly of Valves
Valves are usually assembled according to the sequence and method specified in the process with the valve body as the reference part. Before assembly, parts and components should be reviewed to avoid parts that are not deburred or cleaned from entering the final assembly. During the assembly process, the parts should be handled with care to avoid bumping and scratching the processing personnel. The moving parts of the valve (such as valve stem, bearing, etc.) should be coated with industrial butter. The valve cover is bolted to the valve body. When the bolts are tightened, they should be weighed, interwoven, repeatedly and evenly. Otherwise, the joint surface of the valve body and valve cover will leak due to the uneven stress around it. The handle used for fastening should not be too long, so as to prevent the excessive pre-tightening force from affecting the bolt strength. For valves with strict requirements for preload, torque should be used to tighten bolts according to specified torque requirements. After the final assembly, the holding mechanism should be rotated to check whether the movement of the valve opening and closing parts is mobile and whether there is any jamming. The valve can be tested only after the valve cover, bracket and other parts meet the requirements of the drawings.
