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Valve assembly method, steps and precautions

cowinns cowinns 2023-05-18 11:15:46
Valve assembly method, steps and precautions

ball valve.jpg

Several parts make up the parts of the valve (such as valve cover, valve disc parts, etc.). The assembly process of several parts to form a component is called component assembly, and the assembly process of several parts and components to form a valve is called general 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 will not meet the specified requirements, and even seal leakage will occur. Therefore, special attention should be paid to adopting reasonable assembly methods to ensure the final product quality of the valve. The assembly process defined in the form of documents in production is called the assembly process specification.

There are three commonly used assembly methods for valves, namely complete interchange method, repair method and matching method.

1

full swap

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 shape tolerance. The advantages of the complete interchange method are: the assembly work is simple and economical, the workers do not need a high level of skill, the production efficiency of the assembly process is high, and it is easy to organize assembly lines and organize specialized production. However, in absolute terms, when a complete replacement assembly is adopted, the machining accuracy of the parts is required to be high. It is suitable for valves with relatively simple structures such as globe valves, check valves, and ball valves, as well as medium and small-diameter valves such as 2500LB check valves.

2

matching method

The valve is assembled by matching method, the whole machine can be processed according to economical precision, and then a certain size with adjustment and compensation function is selected and matched during assembly to achieve the specified assembly accuracy. The principle of the matching method is the same as that of the repairing method, except that the way of changing the size of the compensation ring is different. The former is to change the size of the compensation ring by selecting accessories, and the latter is to change the size of the compensation ring by trimming accessories. For example: the top core and adjusting gasket of the control valve model double disc wedge gate valve, the adjusting gasket between the two bodies of the split ball valve, etc., are to choose special parts as compensation parts in the dimensional chain related to assembly accuracy, through Adjust the thickness of the gasket to achieve the required assembly accuracy. In order to ensure that the fixed compensation parts can be selected in different situations, it is necessary to pre-manufacture a set of gaskets and bushing compensation parts of different thickness sizes for hydraulic control valve models for selection during assembly.

3

repair method

The valve is assembled by the repairing method, and the parts can be processed according to economical precision. During assembly, a certain size with adjustment and compensation functions is repaired to achieve the specified assembly target. For example, the gate plate and valve body of the wedge gate valve, because the processing cost required to realize the interchange is too high, most manufacturers adopt the repair method. That is, when the gate sealing surface is finally ground to control the opening size, it is necessary to match the plate with the opening size of the valve body sealing surface to achieve the ultimate sealing requirement. Although this method increases the board matching process, it greatly simplifies the dimensional accuracy requirements of the previous processing steps. The special personnel in the board matching process are skilled in operation, and generally speaking, it will not affect the production efficiency. Assembly process of valves: individual valves are assembled in a fixed site, valve parts and components assembly and general assembly are carried out in the assembly workshop, and all the required parts and components are transported to the assembly work site. Usually component assembly and general assembly are carried out by multiple 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 relatively low requirements for the technical level of workers.

Some manufacturers or high-tech valves also adopt the mode of assembling suspension lines or assembling rotary tables.

After mastering the valve assembly method, we also need to understand the valve assembly steps.

1.   Preparatory work before assembly Before
assembly, the valve parts need to remove the burrs formed by machining and the welding slag left by welding, clean and cut packing and gaskets.

2.   Cleaning of valve parts

3.   As a valve installed as a fluid pipeline control, the inner cavity must be clean. Especially for valves used in nuclear power, medicine, and food industries, in order to ensure the purity of the medium and avoid medium contamination, the requirements for the cleanliness of the valve cavity are more stringent. The valve parts should be cleaned before assembly, and the chips, residual lubricating oil, coolant and burrs, welding slag and other dirt on the parts should be washed and cleaned. Valves are usually cleaned with alkali-added water or hot water (kerosene can also be used for scrubbing) or cleaned in an ultrasonic cleaner. The parts need to be cleaned after grinding and polishing. The final cleaning is usually to brush the sealing surface with gasoline, then dry it with compressed air and wipe it with a cloth.

4.   Packing and Gasket Preparation

Graphite packing is widely used due to its advantages of corrosion resistance, good sealing performance and small friction coefficient. Packing and gaskets are used to prevent medium from leaking through the stem, bonnet and flange joint. These accessories must be prepared for cutting and receiving before valve assembly.

5.    Assembly of the valve

Valves are usually assembled in the sequence and method specified by the process with the valve body as the reference part. Parts and components should be inspected before assembly to prevent undeburred and uncleaned parts 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 active parts of the valve (such as valve stems, bearings, etc.) should be coated with industrial butter. The valve cover and the flange in the valve body are mostly connected by bolts. When tightening the bolts, they should be tightened symmetrically, alternately, repeatedly and evenly, otherwise the joint surface of the valve body and the valve cover will cause the flow control valve to be damaged due to uneven force around it. leakage. The wrench used for tightening should not be too long to prevent excessive pre-tightening force from affecting the bolt strength. For valves with strict requirements on the pre-tightening force, a torque wrench should be used to tighten the bolts according to the specified torque requirements. After the final assembly is completed, the control mechanism should be rotated to check whether the movement of the valve opening and closing parts is flexible and whether there is any jamming. Whether the installation direction of the pressure reducing valve bonnet, bracket and other parts meets the requirements of the drawings, and the valves that have passed all inspections can be tested.