Analysis of the external pressure of the gate valve

Key words: gate valve; valve seat; external pressure; stress analysis

1 Introduction

A gate valve is a commonly used shut-off valve that is used to turn the medium in the line on or off, but is not suitable for regulating the flow of the medium. Its opening and closing member (valve) moves up and down in a plane perpendicular to the center line of the valve inner passage, and cuts off the medium like a gate, so it is called a gate valve. According to the valve flap structure, the gate valve can be divided into a wedge-type elastic gate, a wedge-shaped rigid single gate, a wedge-shaped rigid double gate, a parallel rigid single gate, a parallel double gate, and the like.

Let's take the wedge-type rigid double gate as an example to introduce the force of the gate valve seat.

2 gate valve seat force analysis

The double-sided sealed gate valve is realized by enhancing the thrust of the valve flap to the valve seat, and the contact pressure should be greater than the pressure of the inlet fluid. The disadvantage of this kind of gate valve is that if it is closed in the cold state and then enters the hot state, the valve flap will expand, so that the closed position is clamped, and when the valve is opened again, it will be difficult. This situation is commonly known. "Let's go down." Well-functioning gate valves are all single-sided seals. The parallel gate valve can only be sealed to the seat at the outlet position. The same is true for the standard wedge valve gate valve, where the pressure deforms the inlet side flap and the fluid flows through the inlet side flap until the valve chamber is pressure balanced. This leads to the problem of the strength of the valve seat at the outlet caused by the external pressure of the medium.

As shown in Fig. 1, after the medium enters the cavity of the valve body, it acts on the valve flap on the outlet side (left side), forming a sealing specific pressure at the sealing surface of the left valve seat and the valve disc to prevent the circulation of the medium. At the same time, the medium acts on the gap between the valve body and the left valve seat, so that the outside of the left valve seat is subjected to the medium pressure. In the calculation of the strength of the left seat, it is necessary to analyze the state of the valve seat subjected to external pressure, and the design method using the rule design can not solve such a complicated problem. In this paper, the design of the analytical design is used to check the strength of the wedge double gate valve seat.

Through the analysis of the force of the valve seat, it can be known that the welding between the valve seat and the valve body is a fixed constraint, and the outer cavity of the valve seat is subjected to the pressure of the medium, and the sealing surface of the valve seat is subjected to the sealing pressure of the valve flap.

Transfer the solid model to ANSYS for analysis, select the brick hexahedral element Solid45, the elastic modulus of the input material and the Poisson's ratio (as shown in Table 1), use the free meshing model, and solve the default solver. Stress cloud and strain cloud diagram of the valve seat.

"Table 1" material is 12Cr1MoV

Modulus of elasticity (MPa)	2.140e+006
Bossonby	0.286
Mass density (Kg/mm 2 )	7.86e-012
Yield tensile strength (MPa)	255
Ultimate tensile strength (MPa)	470

According to the stress analysis cloud diagram, the large stress of the valve seat appears in the welded joint between the valve seat inner cavity and the valve seat and the valve body. The shape of the valve seat changes sharply at this position and there is a sharp angle, which should belong to the peak stress. Select the stress evaluation line, classify the stress on the stress assessment line according to the stress classification principle of JB4732-95 (as shown in Table 2), and obtain the film stress and bending stress on the evaluation line, respectively, and compare with the limit value. , you can see whether the seat design is reasonable.

Table 2 Limitations of various stress levels

category	symbol	Calculated	Limit value
Primary film stress	MEMBRANE	Pm	Sm
Primary film + bending stress	MEM+BEND	Pm+Pb	1.5Sm

3 Conclusion Through the stress analysis design method, the stress intensity check of the gate valve seat can be checked, and it can be concluded whether the valve seat design is reasonable.