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Common assembly methods for valves

Date: 2019-10-14        Clicks: 1771

Valve assembly is the final stage in the manufacturing process. Valve assembly is the process of combining the various parts and components of the valve to make it a product according to the prescribed technical premise. The whole machine is the most basic unit of valve assembly, and several parts make up the components of the valve (such as valve cover, disc member, etc.). The assembly process of several parts is called component assembly, and the assembly process of several parts and components that make up the valve is called the total assembly. Assembly work has a great impact on product quality. Even if the design is accurate and the parts are qualified, if the assembly is not proper, the valve will not meet the specified requirements, and even seal leakage will occur. Therefore, special attention should be paid to the use of fair assembly methods to ensure the final quality of the valve. The assembly process defined in document form during production is called the assembly process specification.
Common assembly methods for valves
There are three common assembly methods for valves, namely the complete exchange method, the repair method and the matching method.
(1) Complete interchange method: When the valve is assembled by the full interchange method, each part of the valve can be assembled without any modification and selection, and the assembled product can meet the specified technical requirements. At this point, the valve parts must be machined in accordance with the design requirements, with satisfactory dimensional accuracy and shape tolerance requirements. The strength of the complete interchange method is that the assembly work is simple and economical, the workers do not need a high degree of skill, the assembly process has a high production efficiency, and it is easy to organize the assembly line and organize specialized production. However, in absolute terms, when the complete replacement assembly is adopted, the machining accuracy of the parts is required to be high. It is used for valves such as globe valves, check valves, ball valves, etc., which are absolutely simple in construction, and valves with medium and small diameters.
(2) Matching method: The valve is assembled by the matching method. The whole machine can be processed according to economic precision. When assembling, the size of a certain adjustment and compensation function can be selected to reach the specified assembly precision. The principle of the matching method is similar to the repair method, but it differs in the way of changing the size of the compensation ring. The former uses the method of selecting accessories to change the size of the compensation ring, and the latter uses the method of trimming the accessories to change the size of the compensation ring. For example, the top core of the control valve type double gate wedge gate valve and the adjusting gasket, the adjusting gasket between the two sides of the open ball valve, etc., are the special parts selected in the dimensional chain related to the assembly precision as the compensation component. Adjust the thickness of the gasket to achieve the required assembly accuracy. In order to ensure that the fixed compensating parts can be selected under different conditions, it is necessary to pre-manufacture a set of washers and bushing compensating parts hydraulic control valve models of different thicknesses for assembly.
(3) Repairing method: the valve is assembled by the repairing method, the parts can be processed according to economic precision, and a certain size with adjustment and compensation effect is repaired during assembly to achieve the specified assembly target. For example, the gate and valve body of the wedge gate valve, because the processing cost of implementing the interchange requirement is too high, most manufacturers adopt the repairing process. That is, when the final opening of the sealing surface of the gate is controlled, the opening size of the valve body sealing surface is to be matched with the opening size of the valve body sealing surface to achieve the ultimate sealing requirement. Although this method adds a plate-making process, it greatly simplifies the dimensional accuracy requirements of the previous processing steps, and the person skilled in the plate-making process is skillful to operate, and overall does not affect the production efficiency. Valve assembly process: The valves are individually assembled in a fixed field. The zeros, component assembly and total assembly of the valves are carried out in the assembly shop, and the required parts and components are transported to the assembly work site. Usually, the assembly of components and the total assembly are determined by how many groups of workers are simultaneously performed, which shortens the assembly cycle and facilitates the application of special assembly tools, and the requirements for workers' technical grades are relatively low.
Some foreign manufacturers or high-tech grade valves also adopt the mode of assembling suspension wire or assembling rotary table.
(1) Preparations before assembly: Before the assembly, the valve parts must be removed from the burrs and welding residues of the machining process, and the fillers and gaskets should be cleaned and cut.
(2) Cleaning of valve parts: As a valve for holding the fluid pipe, the inner cavity must be clean. Especially for nuclear power, medicine, food industry valves, in order to ensure the purity of the medium and avoid medium infection, the requirements for the cleanliness of the valve cavity are more stringent. Respond to the valve parts for cleaning before assembly, and clean the chips, residual smooth oil, coolant and burrs, welding slag and other dirt on the parts. The cleaning of the valve is usually carried out with alkaline or hot water (also kerosene) or in an ultrasonic cleaner. After the parts are ground and polished, they need to be finally cleaned. The final cleaning is usually to clean the sealing surface with gasoline, then dry with tight air and wipe with a cloth.
(3) Preparation of filler and gasket: Graphite filler is widely used due to its corrosion resistance, good sealing performance and small friction coefficient. Fillers and gaskets are used to prevent media leakage through the stem and bonnet and flange joint surfaces. These parts must be prepared for cutting and receiving before the valve is assembled.
(4) Assembly of valves: Valves are usually assembled in the order and method specified by the process with the valve body as the reference part. Zero and parts should be reviewed before assembly to avoid parts that are not deburred and not cleaned. During the assembly process, the parts should be handled gently to avoid bumping and scratching the processing personnel. The active parts of the valve (such as valve stems, bearings, etc.) should be coated with industrial butter. The bonnet and the flange of the valve body are mostly connected by bolts. When tightening the bolts, the rivet is called, interwoven, repeated, and evenly tightened. Otherwise, the joint surface of the valve body and the bonnet will be flow-controlled by the surrounding force. leakage. The hand used for fastening should not be too long to prevent the pre-tightening force from being too large and affecting the bolt strength. For valves that have a strict request for pre-tightening force, torque should be applied and the bolts should be tightened according to the specified torque requirements. After the final assembly is completed, the holding mechanism should be rotated to check whether the movement of the valve opening and closing member is maneuverable and whether there is any jamming. Whether the device direction of the valve cover, bracket and other parts of the pressure reducing valve meets the requirements of the drawings, and the valves after passing the review can be tested.