The assembly of the valve is a process that combines all the parts of a valve, which is the last manufacturing process of a valve.
The process of assembling several parts to form a new part is the assembly of a part, while assemble several parts to a whole valve is the general assembly. The assembly greatly influences the quality of the valve. If the valve is assembled not well, the specific requirements can't be met even though there are accurate design and qualified parts. Leakages will even happen. It's important to assemble the valve correctly to make sure that the quality of the valve meets the requirement.
Three assembly methods for valves
The integrated method, adjustment method and selection method are the three commonly used assembly methods for valves.
The integrated method
Every part of a valve can be assembled without any adjustment and selection when a valve is assembled by the integrated method, which meets the specified technical requirements. However, the components of the valve should be manufactured completely based on the design requirements to obtain an accurate dimensional accuracy and geometric tolerance. The integrated method has advantages of simple and economical assembling, not requiring the workers to have much skill, high production efficiency of the assembling, easy organization of assembly lines as well as organized and professional production. When the integrated method is adopted, the requirement for the working accuracy of the component is high. This method is good for a valve with small and medium sizes and simple structure, such as check valves, globe valves, ball valves, etc.
The adjustment method
When the adjustment method is adopted, the part can be processed with economic accuracy. A certain size with functions of adjustment and compensation is adjusted to meet the requirement in the assembling process. For instance, the processing cost of wedges and valve bodies of wedge gate valves are high, so the adjustment method is adopted for most manufacturers. When the sealing surface of the valve plate is ground, it should match with that of the valve body, obtaining the requirement for sealing. The matching process is provided for the adjustment method, but it greatly simplifies the dimensional accuracy requirements in the previous process. The matching process is often performed by a dedicated worker, so the production efficiency won't be influenced. The assembly of valve parts and general assembly are conducted in the assembly workshop. All the needed parts will be sent to the assembly workshop. Generally, the assembling of parts and the whole valve is performed by many groups of workers, which can make the assembling time shorter. In addition, there is a low requirement for the skill of the operator.
The selection method
When the selection method is adopted for the valve, the whole valve can be processed according to economic accuracy. A certain size with functions of adjustment and compensation is selected and matched to achieve the purpose of the specified assembly accuracy in the assembling process. The principle of the selection method is similar to that of the adjustment method, except that the method of changing the size of the compensation ring is different. The selection method changes the compensation ring by choosing parts, while the adjustment method changes the compensation ring by adjusting parts.
The assembly processes
Preparation before assembly
Before the assembly of the valve, burrs caused by machining and welding slags are required to be removed; the valve needs to be cleaned and the packing and gasket should be cut.
The cleaning of valve components
Cleaning of valve parts
As a device controlling the fluid pipeline, the inner cavity ought to be clean, especially valves used for nuclear power, pharmaceuticals, and food industries. To make sure the purity of media and avoid contamination of media, higher requirements are put forward for the cleanliness of the inner cavity of the valve. The valve components are to be washed, including welding slags, chips, coolant, burrs and residual lubricating oil. Alkaline water or hot water can be used for cleaning the valve. Kerosene can also be used. Moreover, a valve can be cleaned in an ultrasonic cleaning machine. Parts should be cleaned after they are ground and polished, which is to remove the dirt on the sealing surface by gasoline. Dry them with compressed air and wipe them with a cloth.
Preparation of the gasket and packing
Graphite packing has advantages of good sealing performance, corrosion resistance, and low friction coefficient, which makes it widely used. Packing and gaskets are used to avoid media from leaking through the valve stem, bonnet and joint surfaces of flanges. They should be cut in advance before assembling valves.
The assembly of the valve
The components of valves should be inspected before assembly to prevent the parts which are not deburred and cleaned from the general assembly. The components of valves should be carried gently to prevent hitting and scratching as well as harming the operator. The industrial grease should be used for the valve's moving parts such as bearings and valve stems. The valve bonnet and flange in the valve body are mainly connected by bolts. The bolts should be tightened well, or leakages will happen due to uneven surrounding forces of the joint surface of the valve body and bonnet. The wrench used for tightening the bolts should not be too long to avoid the pre-tightening force from being too great and affecting the bolt's strength. If there is a strict requirement for the pre-tightening force, a torque wrench should be used to tighten the bolt based on the requirement. When the assembly of the valve is done, check whether or not the opening and closing parts are flexible. There should be no jamming. Check whether or not the installation direction of the valve bonnet, bracket and other parts of the pressure reducing valve meets the requirements for the drawing. Inspect the valve before conducting a test.
The process of assembling several parts to form a new part is the assembly of a part, while assemble several parts to a whole valve is the general assembly. The assembly greatly influences the quality of the valve. If the valve is assembled not well, the specific requirements can't be met even though there are accurate design and qualified parts. Leakages will even happen. It's important to assemble the valve correctly to make sure that the quality of the valve meets the requirement.
Three assembly methods for valves
The integrated method, adjustment method and selection method are the three commonly used assembly methods for valves.
The integrated method
Every part of a valve can be assembled without any adjustment and selection when a valve is assembled by the integrated method, which meets the specified technical requirements. However, the components of the valve should be manufactured completely based on the design requirements to obtain an accurate dimensional accuracy and geometric tolerance. The integrated method has advantages of simple and economical assembling, not requiring the workers to have much skill, high production efficiency of the assembling, easy organization of assembly lines as well as organized and professional production. When the integrated method is adopted, the requirement for the working accuracy of the component is high. This method is good for a valve with small and medium sizes and simple structure, such as check valves, globe valves, ball valves, etc.
The adjustment method
When the adjustment method is adopted, the part can be processed with economic accuracy. A certain size with functions of adjustment and compensation is adjusted to meet the requirement in the assembling process. For instance, the processing cost of wedges and valve bodies of wedge gate valves are high, so the adjustment method is adopted for most manufacturers. When the sealing surface of the valve plate is ground, it should match with that of the valve body, obtaining the requirement for sealing. The matching process is provided for the adjustment method, but it greatly simplifies the dimensional accuracy requirements in the previous process. The matching process is often performed by a dedicated worker, so the production efficiency won't be influenced. The assembly of valve parts and general assembly are conducted in the assembly workshop. All the needed parts will be sent to the assembly workshop. Generally, the assembling of parts and the whole valve is performed by many groups of workers, which can make the assembling time shorter. In addition, there is a low requirement for the skill of the operator.
The selection method
When the selection method is adopted for the valve, the whole valve can be processed according to economic accuracy. A certain size with functions of adjustment and compensation is selected and matched to achieve the purpose of the specified assembly accuracy in the assembling process. The principle of the selection method is similar to that of the adjustment method, except that the method of changing the size of the compensation ring is different. The selection method changes the compensation ring by choosing parts, while the adjustment method changes the compensation ring by adjusting parts.
The assembly processes
Preparation before assembly
Before the assembly of the valve, burrs caused by machining and welding slags are required to be removed; the valve needs to be cleaned and the packing and gasket should be cut.
The cleaning of valve components
Cleaning of valve parts
As a device controlling the fluid pipeline, the inner cavity ought to be clean, especially valves used for nuclear power, pharmaceuticals, and food industries. To make sure the purity of media and avoid contamination of media, higher requirements are put forward for the cleanliness of the inner cavity of the valve. The valve components are to be washed, including welding slags, chips, coolant, burrs and residual lubricating oil. Alkaline water or hot water can be used for cleaning the valve. Kerosene can also be used. Moreover, a valve can be cleaned in an ultrasonic cleaning machine. Parts should be cleaned after they are ground and polished, which is to remove the dirt on the sealing surface by gasoline. Dry them with compressed air and wipe them with a cloth.
Preparation of the gasket and packing
Graphite packing has advantages of good sealing performance, corrosion resistance, and low friction coefficient, which makes it widely used. Packing and gaskets are used to avoid media from leaking through the valve stem, bonnet and joint surfaces of flanges. They should be cut in advance before assembling valves.
The assembly of the valve
The components of valves should be inspected before assembly to prevent the parts which are not deburred and cleaned from the general assembly. The components of valves should be carried gently to prevent hitting and scratching as well as harming the operator. The industrial grease should be used for the valve's moving parts such as bearings and valve stems. The valve bonnet and flange in the valve body are mainly connected by bolts. The bolts should be tightened well, or leakages will happen due to uneven surrounding forces of the joint surface of the valve body and bonnet. The wrench used for tightening the bolts should not be too long to avoid the pre-tightening force from being too great and affecting the bolt's strength. If there is a strict requirement for the pre-tightening force, a torque wrench should be used to tighten the bolt based on the requirement. When the assembly of the valve is done, check whether or not the opening and closing parts are flexible. There should be no jamming. Check whether or not the installation direction of the valve bonnet, bracket and other parts of the pressure reducing valve meets the requirements for the drawing. Inspect the valve before conducting a test.
Next: Design Requirements for Main Parts of Nuclear Power Valves (Part One)
Previous: The Selection of Abrasive Materials and Tools of Valves