Common assembly methods of valves
Valve assembly is the last stage in the manufacturing process. Valve assembly is the process of combining all parts and components of the valve together to make it a product according to the specified technical premise.
The whole machine is the most basic unit of valve assembly, and several parts constitute the valve parts (such as valve cover, valve disc parts, etc.). The assembly process of several parts is called component assembly, and the assembly process of several parts and components is called 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 improper, the valve can not meet the requirements of the regulations, and even produce valve seal leakage. Therefore, special attention should be paid to the use of fair assembly methods 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 common assembly methods for valves, namely complete replacement method, repair method and selection method.
Complete interchange method
When the valve is assembled by complete interchange method, each part of the valve can be assembled without any repair and selection, and the assembled product can meet the specified technical requirements. At this time, the valve parts should be processed in full accordance with the design requirements to meet the requirements of dimensional accuracy and geometric tolerance. The advantages of the complete exchange method are: the assembly work is simple and economical, the workers do not need a high degree of skills, the production efficiency of the assembly process is high, and it is easy to organize the assembly line and professional production. However, absolutely speaking, when complete replacement assembly is adopted, the machining accuracy of parts is required to be higher. It is applicable to globe valve, check valve, ball valve and other valves with simple structure, as well as medium and small diameter valves.
The valve is assembled by selection method, and the whole machine can be processed according to the economic precision. When assembling, a certain size with adjustment and compensation effect can be selected to achieve the specified assembly precision. The principle of the selection method is the same as that of the repair method, but the way of changing the size of the compensation ring is different. The former is to change the size of compensation ring by selecting accessories, while the latter is to change the size of compensation ring by trimming accessories. For example: the top core and adjusting gasket of the control valve type double ram wedge gate valve, the adjusting gasket between the two bodies of the split ball valve, etc., is to choose the special parts as compensation parts in the dimension chain related to the assembly accuracy, and 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 washer and shaft sleeve compensation parts with different thickness and size in advance for hydraulic control valve model selection during assembly.
The valve is assembled by repair method, the parts can be processed according to the economic precision, and then a certain size with adjustment and compensation effect can be repaired during assembly, so as to achieve the specified assembly goal. For example, the gate and valve body of wedge gate valve, because of the high processing cost of realizing the exchange requirements, most manufacturers adopt the repair process. That is to say, in the final grinding of the gate sealing surface to control the opening size, the plate should be matched according to the opening size of the valve body sealing surface, so as to achieve the ultimate sealing requirements. This method increases the plate matching process, but greatly simplifies the dimensional accuracy requirements of the previous processing process. The skilled operation of the plate matching process by special personnel will not affect the production efficiency on the whole. Valve assembly process: the valves are individually assembled in a fixed site. The assembly of parts and components and the general assembly of the valves are carried out in the assembly workshop, and all the necessary parts and components are transported to the assembly site. Usually, how many groups of workers are responsible for the assembly of parts and the General Assembly 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 the technical level of workers.
Some foreign manufacturers or high-tech grade valves also adopt the mode of assembly suspension line or rotary table.
Preparation before assembly
Before assembly of valve parts, it is necessary to remove the burr formed by machining and welding residue, clean and cut the filler and gasket.
Cleaning of valve parts
As a fluid pipeline control installation of the valve, the cavity must be clean. Especially for the valves used in nuclear power, medicine and food industries, in order to ensure the purity of medium and avoid medium infection, the requirements for the cleanliness of valve cavity are more stringent. Before assembly, the valve parts should be cleaned, and the chips, residual smooth oil, coolant and burr, welding slag and other dirt on the parts should be cleaned. Valve cleaning is usually done with water or hot water with alkali (kerosene can also be used for cleaning) or in ultrasonic cleaning machine. Parts need to be cleaned after grinding and polishing. The final cleaning is usually to brush the sealing face with gasoline, then blow dry with compressed air and wipe it with cloth.
Preparation of packing and gasket
Graphite packing is widely used because of its corrosion resistance, good sealing performance and low friction coefficient. Packing and gasket are used to prevent leakage of medium between valve stem, valve cover and flange joint face. These accessories should be prepared for cutting and receiving before valve assembly.
Valve is usually the valve body as a benchmark parts, according to the order and method of process requirements for assembly. The parts and components should be reviewed before assembly to avoid the parts without deburring and cleaning entering the final assembly. In 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 stem, bearing, etc.) should be coated with industrial grease. The flange in the valve cover and the valve body are connected by bolts. When tightening the bolts, they should be tightened in response, interweave, repeatedly and evenly. Otherwise, the joint surface of the valve body and the valve cover will produce leakage of the flow control valve due to the uneven stress around. The handle used for fastening should not be too long to prevent the bolt strength from being affected by the excessive pre tightening force. For valves with strict requirements for preload, torque handle shall 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 jamming. Whether the installation direction of the valve cover, bracket and other parts of the pressure reducing valve meets the requirements of the drawing, and the valve can be tested only after all the reviews have passed.
Source: China Valves Manufacturer – Yaang Pipe Industry Co., Limited (www.pipelinedubai.com)
(Yaang Pipe Industry is a leading manufacturer and supplier of nickel alloy and stainless steel products, including Super Duplex Stainless Steel Flanges, Stainless Steel Flanges, Stainless Steel Pipe Fittings, Stainless Steel Pipe. Yaang products are widely used in Shipbuilding, Nuclear power, Marine engineering, Petroleum, Chemical, Mining, Sewage treatment, Natural gas and Pressure vessels and other industries.)
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