The spring set elastic valve seat is a valve sealing structure in which a set of compression springs are evenly arranged on the circumference of the cross section of the valve fluid passage, and the sealing force is brought into close contact with the ball by the thrust of the spring to achieve a pre-tight sealing function.
    When the spring set elastic seat is used in a fixed ball valve, an elastic seat is placed in front of and behind the valve of the ball valve. Such an arrangement can realize the valve front seal of the ball valve, the post-valve seal and the double-sided seal of the valve front valve in the case of changing the geometric parameters of the ball valve. For these three types of seals, the structure is similar but the characteristics are different, which can meet different work needs. Therefore, the spring set elastic seat is used in the fixed ball valve, regardless of high temperature, low temperature and normal temperature.
   2 spring set elastic seat
    The spring set elastic valve seat is a valve sealing structure that uses a spring set to achieve a pre-tightened contact seal and relies on fluid pressure to achieve a seal. The specific structure diagram is shown in Figure 1.
1. Valve body 2. Spring 3. Seat seal 4. Seat
5. Ball seal ring 6. sphere
Figure 1 spring set elastic seat
    Where d 1 is the median diameter of the valve body contact surface; d 2 is the median diameter of the ball contact surface. The relationship between the size of d 1 and d 2 is the key to determining the three sealing forms of the spring set elastic seat. When d 1 >d 2 , the spring group elastic valve seat is the valve front sealing valve seat; when d 1 <d 2 , the spring group elastic valve seat is the valve rear sealing valve seat; when d 1 >d 2 ;d 1 ' For <d 2 ' , the spring set spring seat is a double-sided sealed seat.
   2.1 spring group elastic seat valve front seal
    When d 1 >d 2 , the spring group elastic valve seat is a spring group valve front sealing elastic valve seat structure as shown in FIG. 2 . At this time, the fluid pressure receiving area A1 of the valve seat is larger than the reverse pressure receiving area A2 of the ball sealing ring. At this time, the valve front seat is under the action of the spring pre-tightening sealing force and the pressure difference between the pressure of the A1 and A2 pressure receiving surfaces, and the spherical sealing ring is tightly attached to the ball to achieve the sealing of the valve. At this point, the valve seat does not seal.
Figure 2 Spring group valve front sealing elastic seat
    There is no clear definition of the structure of the valve seat behind the valve. The design needs to be determined according to the pressure relief form of the valve body cavity. For the body cavity pressure relief fluid of this structure before the pressure relief fluid is discharged to the valve, a large part of the body cavity fluid cannot be eliminated due to the pressure of the fluid in the valve body. After the pressure relief fluid is discharged to the valve, the downstream pressure drop can remove most of the fluid in the body cavity when the valve is closed. When the pressure relief fluid is discharged to the rear structure of the valve, the valve seat structure must adopt a structure in which the pressure receiving area A3 of the cavity is larger than the pressure receiving area of ​​the outer valve seat A4, as shown in FIG.
Figure 3 valve rear seat structure
    This structure: d 1 ' > d 2 ' ; A 3 > A 4 . When the pressure in the middle chamber rises, the pressure seat area A3 of the fluid seat is larger than the reverse pressure receiving area A4 of the valve seat. Under the action of the differential pressure thrust of the fluid, the ball and the ball seal are pushed open, and the high pressure medium cavity fluid is discharged into the valve after the valve. Go and achieve pressure relief.
    For the valve front seat seal, the advantages are: the stuffing box of the valve, the valve cover and most of the valve body do not need to withstand the pressure of the fluid; the valve body cavity does not have a large amount of medium erosion filler, valve cover, etc.; when the body cavity is unexpectedly boosted, The fluid is quickly drained to avoid impact on the valve; no fluid build-up area is formed after the valve. Therefore, the valve front seat seal is particularly suitable for corrosive media and cryogenic liquid gasification. Disadvantages: the sealing force acts on the sphere, the torque load required to rotate the sphere is large, and the valve stem is subjected to a large driving thrust; the calculation accuracy of the sealing specific pressure is high, and when the sealing ratio is too large, it will cause The valve seat overload and the ball rotation torque are large; when the sealing specific pressure is small, the valve seat seal will be invalid; it can only be used within a certain pressure range.
 2.2 spring group elastic valve seat valve rear seal
    When d 2 >d 1 , the spring group elastic valve seat is a spring group valve and the sealing elastic valve seat structure is as shown in FIG. 4 .
Figure 4 Spring set valve rear seal elastic seat
    When d 1 > d 2 , the front seat fluid pressure receiving area A 1 is smaller than the ball seal reverse pressure receiving area A 2 . At this time, under the action of the pressure difference between the pressures of A 1 and A 2 , the fluid pushes the ball seal away from the sphere, creating a fluid gap passage, and the fluid enters the body cavity of the ball valve. Then, the fluid pressure receiving area A 3 of the valve seat is smaller than the pressure receiving area A 4 . Into the medium in the chamber, is generated in the pressure-receiving surface A3 and A 4 pressure thrust, the rear valve seat ring firmly attached to the ball, sealing the valve.
    For the valve rear sealing spring group valve rear sealing elastic valve seat, the valve front valve seat and the valve rear valve seat structure are basically the same. Valve front seat: d 1 <d 2 ; A 1 <A 2 . Valve rear seat: d 1 ' <d 2 ' ; A 3 <A 4 .
    For valve rear seat seals, the advantage is that the fluid enters the body cavity and is sealed with the rear seat. Therefore, the effective force of the fluid pressure on the ball and the valve seat is small, the torque required for the rotation of the ball is small, and the force on the stem bearing is small. Therefore, it is suitable for high pressure and large diameter applications. The bearings are self-lubricating. Disadvantages: The fluid always exists in the body cavity, which is unfavorable for the packing, the bonnet seal and the valve body; it is not suitable for controlling corrosive fluids; it cannot be automatically relieved, and the low pressure liquid gasification occasion must be used, and the pressure relief device must be provided; To ensure d2>d1, the flow diameter is reduced or the size of the sphere and valve body is increased.
  2.3 spring group elastic valve seat double-sided seal
    When d 1 >d 2 ;d 1 ' <d 2 ' , the spring group elastic valve seat is a spring group double-sided sealing elastic valve seat structure as shown in FIG. 5.
Figure 5 Spring set double-sided sealing elastic seat
    The spring group double-sided sealing elastic valve seat is actually a combination of the spring group elastic valve seat valve front and the valve rear seal. Valve front seat: d1>d2; A1>A2; valve seat: d1'<d2'; A3<A4. In this way, whether the fluid in the body cavity is not infiltrated or the more or less fluid is infiltrated above or below the pressure of the fluid in the pipe, the sealing effect of the ball seal on the valve can be achieved.
    For the double-sided seat seal, the advantages are: the sealing performance is reliable; there will always be more or less fluid entering the middle cavity, and a certain pressure will be exerted on the ball and the valve seat, and the rotational torque load of the ball is small. Therefore, it is used in places where sealing requirements are high. Disadvantages: Double-sided seat seals cannot achieve automatic pressure relief. Therefore, when controlling the liquefied gas, it is necessary to provide a pressure relief device.
  3 conclusions
    Fixed ball valve spring set The elastic seat is a sealing structure involving high, low and normal temperature and is widely used. The three types of sealing structures have different characteristics and must be selected correctly when applied. The sealing pressure ratio is affected by the pressure difference driving force of the pressure receiving area, the preloading spring force and the sliding friction force. At the same time, it is greatly affected by the pressure difference of the pressure area. However, the diameters of the two pressure-receiving surfaces are generally not much different. Therefore, accurate calculations must be made during design.
    (1) The relationship between the diameter d 1 of the valve body contact surface of the elastic ball seat of the fixed ball valve spring group and the diameter d2 of the ball contact surface determines the three sealing forms of the valve.
    (2) The sealing specific pressure of the elastic valve seat of the fixed ball valve spring group (that is, the reliability of the sealing) mainly depends on the proportional relationship between the diameter d1 of the valve body contact surface and the diameter d 2 of the ball contact surface .
    (3) For the three sealing structures, the valve seat seat seal can be used in the corrosion and liquefied gas with pressure P≤10MPa and the valve diameter is large; the valve seat seal is usually used for pressure P ≥16MPa 80-100 diameter valve; double-sided seal, especially for dangerous places with high sealing requirements. Three fine valve technology provides
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