Optimized Intermediate Flange Structure of Nuclear Grade Large Diameter Gate Valves (Part Two)

3.2 Reducing center of gravity, dead-weight and heights of the part and whole valve
The main factors affecting the anti seismic performance of the valve are dead-weight and center of gravity of the valve extension mechanism. The main components include the valve body extension, bonnet, bracket and electric actuator. Compared with a split flange structure, the main structural changes are the valve bonnet and bracket for the valve adopting an integral intermediate flange structure. The integral intermediate flange structure simplifies the bonnet, reduces the height, center of gravity of the bonnet and its own weight, but at the same time expands the size of the flange connecting to the bracket and bonnet, making dead-weight of the bracket of the integral intermediate flange structure (Figure 7) increased compared with dead-weight of the bracket with split flange structure (Figure 8).

Figure 7 Integral intermediate flange structure brackets
 
Figure 8 Split type integral intermediate flange structure brackets
 
The dead weight, height and longitudinal center of gravity of bonnets and brackets of the two structures are compared. The specific data are shown in Table 1.
 
Table 1 A comparison of partitioning data

 
It can be concluded from Table 1 that when the gate valve adopts the integral intermediate flange structure, the mass of the bracket increases by 28.1kg, but it is far less than the weight reduction value of the valve bonnet of 66.5kg. In addition, the partitioning height and longitudinal center of gravity of the valve bonnet and bracket of the integral flange structure are less than or equal to corresponding parameters of the split flange structure, which is beneficial to guaranteeing the anti seismic performance of the valve. Then compare the two structures from the height, size of longitudinal center of gravity and dead-weight of the whole valve. See Table 2 for specific data.
 
Table 2 Data comparison of the whole valve

 
It can be concluded from Table 2 that when the valve adopts the integral intermediate flange structure, the height, size of longitudinal center of gravity and quality of the whole valve are all reduced, that is, the integral intermediate flange structure helps to ensure the anti seismic performance of the valve.
 
3.3 Increasing the cross-sectional area, moment of inertia, bending modulus and torsional modulus of the dangerous section
Compared with the split flange structure, the main change is the 4-4 bracket root section for the valve adopting the integral intermediate flange structure. The integral intermediate flange structure expands the flange size of the bracket connected to the valve bonnet so that the outer circle size of the bracket can be maximized. The cross-sectional properties of the two structures are compared in Table 3.
 
Table 3 Comparison of 4-4 section properties of bracket roots

 
It can be seen from Table 3 that when the gate valve adopts the integral intermediate flange structure, the cross-sectional area, moment of inertia, bending modulus, torsional modulus and other parameters of the 4-4 bracket root section have a great increase, which are more conducive to ensuring the anti seismic performance of the gate valve.

4 Test verification
4.1 Theoretical analysis
The analysis model is DN250 large diameter electric high-pressure gate valve with both integral intermediate flange structure and split flange structure. The electric actuator is set as a mass point, and the constraint condition of the valve inlet and outlet is set as a fixed constraint. Each model is meshed separately. Through calculation, natural frequency of the integral intermediate flange structure is 54.8HZ (Figure 9), and natural frequency of the split flange structure is 44.8HZ (Figure 10).

 
Figure 9 Natural frequency analysis of the integral type


Figure 10 Natural frequency analysis of the split type
 
From the perspective of modal analysis, it can be concluded that natural frequency of the integral flange structure is higher, which is more conducive to ensuring the anti seismic performance of the valve.
 
4.2 Prototype test verification
In order to verify that the large diameter electric high-pressure gate valve with a size of DN250 and integral intermediate flange structure has good anti seismic performance, the valve is subjected to a detection test of dynamic characteristics and seismic static load test (Figure 11).

 
Figure 11 Identification test

The test results show that the natural frequencies of the three orthogonal directions of valves are all greater than 44HZ, and the valve opens and closes normally, runs smoothly and can keep the pressure boundary intact under load. It can be concluded that the electric high-pressure gate valve with a large diameter of DN250 and integral intermediate flange structure has good anti seismic performance.
 

5. Conclusion
1. The weight of the whole gate valve is reduced by 49kg for electric high-pressure gate valves with a large diameter of DN250 adopting an integral intermediate flange structure, and the weight reduction ratio is 23%, which have achieved the effect of reducing costs.

 

2. Valves with integral flange structure only need to tighten one set of nuts, while two sets of nuts need to be tightened to connect the valve body, bonnet and bracket for valves with split flange structure, which increase work efficiency.

 
3. The electric high-pressure gate valve with large diameters can have good anti seismic performance by adopting the integral intermediate flange structure; the integral intermediate flange structure can be used as an effective measure to ensure the anti seismic performance of the electric high-pressure gate valve with large diameters, and it can also play the role of cost reduction and efficiency enhancement.