The Structure of Nuclear-grade Large-diameter Ultra-long Distance Gate Valves

1. The structure design of the valve 
The valve is a non-rising stem elastic wedge gate valve. The valve body and bonnet adopt integral casting. The body cover is connected by a middle flange and a bolt, which is sealed with 304L flexible graphite plates. The middle cavity of the body cover is an elliptical structure. A reinforcing rib is provided to make the valve bonnet’s external part have enough strength and rigidity (analyzed with ANSYS). The connection between the bonnet and the upper bonnet is a flange and a bolt structure, and a wound gasket plus an anti-overpressure sealing structure is adopted. The valve stem is sealed with packing, and the valve end is a flange structure, which meets the requirements of ASME B16.47. All fasteners are securely locked with double lug stop washers and the manual operating device is set on the water.
 
The remote transmission mechanism adopts a rigid shaft remote transmission mechanism, using about 6 steel pipes with a size of 60×1500mm. On the remote operating mechanism, one IE level limit switch is installed in the fully open and fully closed positions, and the opening and closing position indicator is installed on the valve. The remote operating mechanism is designed with a failure breaking point at the handwheel. When the breaking occurs, the torque at the handwheel is 450N·m. The hand wheel on the remote operating mechanism can be removed, and the hand wheel can be installed again for operation when required.
 
The valve and the remote transmission, and the remote transmission and the manual device are all connected by keys. The momentary moment of torque is 504.8N·m when the valve is opened, and the moment of torque in the opening of the valve is 100N·m. The momentary moment of torque when the valve is closed is 978.27N·m calculated based on the maximum pressure difference of 406.8kPa. The transmission efficiency of the remote operation mechanism is about 80%; the transmission ratio of the manual device is 6:1, and the transmission efficiency is 4.83 (about 80.5%). The handwheel operating force is less than and equal to 450N when the valve is opened. The handwheel operating force is less than and equal to 100N in the opening process of the valve, and the handwheel operating force is less than and equal to 850N when the valve is closed. The valve and the remote operating mechanism need to carry out linkage tests, and after the linkage test, the valve with linkage operations should also be tested for sealing. The total stroke of the valve is about 790mm, and the number of rotations of the handwheel is 174, which meets the requirement for 200 turns.
 
1.1 The structure of valve bodies and bonnets 
The valve body and bonnet of the valve adopt the casting structure. While ensuring the minimum wall thickness, the valve body and bonnet are casted with reinforcing ribs to ensure strength and rigidity of the valve body and bonnet. Restricted by the valve structure length of 559mm, the middle cavity adopts a quasi-elliptical structure, and the middle cavity gasket adopts a 304L flexible graphite plate. The guide rib on the valve body adopts a split structure; the surface of the guide rib is surfacing with STL21, and then the guide rib is welded to the valve body. In terms of quality control, radiographic testing and liquid penetrant testing should be carried out in strict accordance with non-destructive testing regulations.
 
1.2 The structure of the wedge 
The wedge adopts an integral casting structure. The wedge is elastic, and its sealing surface is surfacing with STL6 hard alloys. After processing, the thickness of the alloy layer is not less than 3.2mm. The wedge of the guide groove is surfacing with STL21 hard alloys, and the thickness of the alloy layer after processing is not less than 3.2mm.
 
1.3 The structure of the stem
The valve stem seal adopts low-torque group packing, which is reliable in sealing and can reduce valve torque. The middle part of the valve stem is designed with a boss to prevent the valve stem from moving up and down, and the thrust bearings of corrosion-resistant materials are arranged on the upper and lower sides of the valve stem boss, which can reduce the torque. The middle part is equipped with a shaft sleeve made of QAl9-4, which can not only reduce the torque but also play the role of radial support.
 
1.4 The analysis and calculation of the design of the valve 
Carry out the following analysis and calculation on the valve, so that the product performance can be verified in theory:
(1) Calculating the strength of main parts: According to ASME, perform strength calculation and stress analysis of main parts such as valve bodies, wedges, valve stems, valve bonnets and valve seats.
(2) Calculating natural frequency. The natural frequency of the whole valve is calculated, and the calculated natural frequency of the valve is greater than the 33Hz required by the specification.
(3) Analyzing the risk section: The equivalent static method is used to carry out seismic analysis on the dangerous section of the valve according to the load combination of design pressure, self-weight, dynamic load and valve driving force. The stress of each dangerous section is within its allowable stress range and meets the design requirements.
(4) Analyze the middle flange and bolt.
(5) Analyze the strength and deformation of the valve body and bonnet.
(6) Analyze the anti-seismic theory for remote operation.
(7) Carry out the calculation of the valve torque, and select appropriate remote operating mechanisms and manual devices according to parameters such as torque.