The Optimal Structural Design of the Large Wedge Gate Valve (Part Two)

Aug 19, 2021

2.3 The design and verification of valve stems
A valve stem is the main part of a valve. If the valve is deformed or broken during use, it will cause an accident. Therefore, the strength of the valve must be checked to ensure that it can withstand the force within a certain range. 20Gr13 is used as the valve's material, which has good plasticity, toughness and wear resistance after heat treatment. The outer diameter of the valve is set to 70 mm, and the inner diameter 52 mm. The gate valve has two states, that is a closed state and an open state, so it is necessary to realize the force analysis in different states. The analysis of axial force is focused on in this article. When the valve is opened, the formula for calculating the axial force on the valve stem is QFZ=Q+QT-QP. When the valve is closed, the calculation formula of the axial force on the valve stem is QFZ=Q +QP-QT. The QP in the formula refers to the axial force applied by the medium to the valve. The formula is QP=( π-4)dF2P=4.52kN. The dF in the formula is the diameter of the valve stem. P means the medium pressure, and QT is the friction between the valve stem and filling material. The calculation formula is QT=π dFhTuTP=1.36kN. The hT in the formula refers to the total height of the filler; uT is the friction coefficient between the filler and valve stem, which is calculated by asbestos, and the friction coefficient is set to 0.15.

Through the above formulas, the axial force is calculated to be 109.6kN when the valve stem is closed, and the axial force is 161.84kN when the valve stem is opened. In this way, the final result is obtained. The axial forces are 115.48kN and 158.68kN when the valve is opened or closed.

It can be seen that the shear force should be checked in the verification process of the stem's strength to fully verify whether the stem head's strength meets actual needs.

2.4 The design of stress intensity
When the parameter reaches a certain value, the stress value is the smallest. The variable optimization result is obtained. The three-dimensional graph is the actual response graph, and the global solution in the range of relief constraints is obtained. Through stress design and strength stress analysis, the thickness of the ribs on both sides of the valve body and the thickness of the valve body specified will affect the maximum stress of the valve body, followed by the rounding radius where the middle cavity interface shape intersects with the circle.

3. Optimized results
The influence of the finite element optimization program on the strength of the valve body is optimized. Table 1 shows the improved results of the valve body's structure. After the modification, the large circle radius of the valve body cavity's section is reduced, and the radius of the intersection of the large and small circles is increased; the section's shape is similar to an ellipse. The interface bears force uniformly. The lateral length of the reinforcing rib's shape outside of the valve body is reduced, and the bearing force of the valve body cavity is guaranteed, which can reduce the stress concentration of the valve body. The improvement results show that this improvement can ensure the strength of the valve body and meet the actual work requirements.

Table 1 The improvement results of valve body's structure

Design variable	Before improvement	After improvement
Big radius circles of sections of middle valve cavities/mm	2100	2075
The thickness of the three reinforcing ribs on the outside of the valve body D1/mm	35	35
The thickness of the valve body/mm	32	32
The lateral length L1 of the interface shape of the three reinforcing ribs on the outside of the valve body /mm	93	88
Distances between the first reinforcing rib and the middle flange/mm	60	60
Distances between the second and third reinforcing ribs/mm	95	92.5
The thickness of the ribs on both sides of the valve body/mm	30	60
The weight of the valve body/kg	1280	1284.5
Maximum equivalent stress	143	116.5
The rounding radius R2 of the intersection of large and small circles of the middle valve cavity /mm	40	45

4. Conclusion
The wedge gate valve with large diameters is optimized in this article. Select various parts reasonably, and optimize each size. In addition, the stress analysis of various parts and the strength check of the design standards indicate that the design can meet the required strength.