Abstract: The seal structure was discussed about stainless steel spherical valve, the factors of the key seal structure and the seal material of spherical valve that affected the sealing and using performance and the reliability was analyzed, and the combination seal structure of distensible circle and labial structure of PTFE was proposed.
Keywords: Spherical valve; Seal structure; Combination seal structure
Ball valve with its well-known, widely used in various pipeline systems quickly cut off, change the media flow and control, can use manual, electric or pneumatic drive means. Figure 1 shows a typical valve structure (not to consider drive mode).
Figure 1
Performance in the ball valve, the seal is one of its main targets. Figure 1 shows that the valve sealing structure consists of three parts, one of the main seal between the vice body, the sealing gasket to adjust to achieve; the other between the main valve body and valve stem seals, from the standard "V" -shaped filler or 0 -ring to achieve, the composition of the outer valve seal structure. The third was the main sphere, deputy seal between valve body, achieved by the seal seat to form the main valve seal structure. The main valve seal structure affect the work of sealing performance, are the key design and manufacture of ball valve sealing structure. This article will focus on non-metallic sealing ball valve main seal (also known as soft-sealed) structure.
A valve sealing requirements
Ball valve seal leakage and external indicators of leakage from the requirements within the established national standard non-metallic sealing ball valve sealing by GB/T13927 " Universal Valve Pressure Test " A-level implementation, calling for " sustained period of time without trial Visible leakage "; aerospace industry standard for gas piping systems provides ground ball "in 0.05MPa and 1.1 times the nominal pressure of the air pressure conditions, the holding pressure 3min, internal leakage rate should not exceed 3 × 10-5Pa · m3/ S (no bubbles escape); at 1.1 times the nominal pressure of the air pressure conditions, the holding pressure 3min, external leakage rate should not exceed 1 × 10-5Pa · m3/ S (no bubbles escape). "
2 in the main due to valve tightness
Factors affecting the main factors valve seal sealing surface roughness and roundness parameters sphere. As we all know, regardless of how advanced processing technology, can not completely eliminate ball roundness error and the sealing surface defects, so in order to achieve good sealing effect, and Bao Zheng Guo Cheng processing can be realized, must determine the appropriate sealing surface roughness And ball roundness parameter values. Information recommendation, ball sealing surface roughness Ra value of the maximum allowable value of 0.4μm; sealed Block roughness Ra value with PTFE sealing material for the maximum allowable value of 0.8μm. Spherical roundness tolerance, according to GB/T1184 accuracy of Schedule 2 of 6 more appropriate.
3 ball valve sealing structure of the main
Early valve, commonly used as a sealing structure of metal material (or seal), with the engineering plastics technology, particularly the emergence of poly ethylene atmosphere, so that valve seal structure has an ideal sealing material. Common seal structure of the main valve seal in the form of soft rigid sealing seat, with elastic components of seal seat, PTFE lip seal seat and flexible expansion ring and PTFE lip seal seat of a combination of seal seat Form. Block lip seal with the lip structure, it has good flexibility in use to ensure the sealing surface of the pre-compression on the sealing surface can be pre-compression and better than the rigid structure of compensation. But the use of found, PTFE plastic deformation and temperature conditions in the stability is still not very satisfactory, and tend to have large cold; the same time, the use of valve pressure varies from Therefore, the use of PTFE as a sealing material of the lip seal seat, in the low pressure conditions, or long-term use is still easy to produce leakage. Way to solve this problem using flexible expansion ring and PTFE lip seal seat of a combination of seal seat, it can rely on flexible metal expansion ring good plastic deformation, plastic deformation to enhance their overall ability and compensation, raise of sealing ability.
3.1 Ball Valve seal condition
To ensure the required sealing ball valve requirements, to promote the ball with the pressure medium (floating ball) or the seal seat (fixed ball valve) produces small displacement, so that sealing seat surface of some plastic deformation, the formation of the necessary Than the pressure seal. Seal than the seal pressure is too high will cause Block suffered more than the material than the allowable pressure than the pressure and damage to seal failure, will result in increased operating torque affect movement performance; too low then will seal the surface of the shells Block Deformation, not compensate the sphere of processing error, causing the main seal can not achieve the required sealing requirements.
Of sealing conditions : qMF <Q <[q]
Type in : qMF – ensure that the sealing surface must be sealed by the specific pressure; [q] – sealing surface of the allowable specific pressure; q – calculating the actual ratio of pressure.
3.2 Floating ball seal mechanism
Figure 1 (a) shows, as ball bearing at the bottom without a fixed, floating ball valve closed, pressure in the medium, the ball will produce a certain amount of float (displacement), left -side sealing seat and pressed the population in the export Side sealing seat, so sealing medium in the Block by block the export side. That is actually floating ball valve seat seal only outlet to play a seal, while the population of end seal between the seat and the ball float to maintain a small gap.
3.3 Fixed ball valve seal mechanism
High-voltage or nominal diameter DN ≥ 200mm of the ball, often with fixed structure. Fixed ball valve floating ball does not produce the amount of guaranteed two-way sealing, reduced torque operation of the valve; sealing seat load less volatile. Fixed ball valve can be divided into pre-sealed (sealed the population) and the ball after the sealed (export sealed) ball valve, shown in Figure 2.
Figure 2
3.4 Ball valve consider the pre-compression seal seat
To ensure the ball low in the medium working pressure sealing, and sealing ball seat must be a certain degree of pretension between the specific pressure.
In the rigid sealing seat, the valve working right choice depends on the reliability and service life of the pre-compression seal seat. Insufficient pre-compression and can not guarantee that the low pressure valve seal; excessive pre-compression, will result in ball and seat seal friction torque between the increase in performance affect ball movement; and may cause the plastic deformation of sealing seat, resulting in seal Failure. PTFE seal for the seat, the sealing pressure ratio should normally be for the 0.1PN, and not less than 1.02MPa. Pre-compression of rigid seal seat adjustments by changing the thickness of the sealing gasket to adjust to achieve, sealing gasket to adjust the error will affect the adjustment process results; reasonable assembly and adjustment is the key to get a good seal. In use, the sealing seat wear, the preload pressure autoregulation capacity than the poor, so rigid valve seat for sealing relatively short life.
One way to solve the problem by sealing seat with elastic components. At this point, pre-compression is no longer rely on the acquisition and adjustment of sealing gasket to adjust to achieve by the elastic element. Seal seat with elastic elements necessary than available pre-compression and also, for the elastic deformation of the elastic element within the sealing pressure ratio compensation, therefore, the ball valve ‘s service life longer.
3.5 Sealed with elastic element seat structure
(L) for the butterfly spring elastic element sealing seat, shown in Figure 3.
Figure 3, the sealing seat with butterfly spring
(2) elastic element sealing seat for the spring, shown in Figure 4.
Figure 4, the seal with cylindrical coil spring seat
Figure 3, Figure 4 shows with a butterfly spring or spiral spring with a cylindrical seal seat valve in non-corrosive media is widely used. However, because of the difficulty chosen to be resistant to corrosive media, while also has good material Yiji flexible elastic elements such materials heat treatment process is relatively Fuza, such sealing seat structure in the strong corrosive medium ball in Yingyong not Duo.
(3) Combined lip seal seat
Figure 5 a combination of elastic expansion ring -type lip seal seat
Figure 5 shows the flexible expansion ring and PTFE lip seal seat combination seal seat. Expandable elastic material choice 1Cr18Ni9Ti or 1Cr18Ni9, in order to achieve compatibility with corrosive media. Figure 6 for the flexible expansion ring structure; Figure 7 for the PTFE lip seal seat structure. From Figure 6, Figure 7 can be seen, poly ethylene atmosphere lip seal lip design seat angle 30°, while the flexible expansion ring lip for 34°.
Figure 6 Block elastic expansion seal ring structure chart
Figure 7 PTFE lip seal seat chart
In the medium pressure, the elastic ring expansion elastic force to compensate for a single seat PTFE seal plastic deformation of the shortcomings of inadequate capacity, improve reliability and service life of valve seal. Low pressure in the medium case, because flexible expansion ring and PTFE lip lip lip seal seat angle difference and the existence of strong metal Expandable plastic deformation, so that PTFE lip seal seat Elastic Expandable elastic force formed outside the sheets tend to the ball compression, resulting in pre-compression force, the compensation medium pressure lower than the pressure caused by inadequate sealing. As long as the elastic expansion of the elastic force within the ring, you can ensure that the pressure conditions in the lower valve reliable seal.
3.6 Floating ball seal seat structure
Floating ball seal seat structure shown in Figure 8.
Figure 8 rigid seal seat
Figure 8 shows the rigid seal seat itself is not flexible deformation, ball Wanquanyikao the sealing medium Yali Xingchengbixu specific pressure The architecture is significant change in temperature of, sealing and operation of torque Yishou temperature change.
Figure 9 Block lip seals
Lip seal shown in Figure 9 Block because the elastic deformation of the lip has a certain ability to seal between the seat and ball there is always a certain size of the pre-compression force, can compensate for temperature changes causes changes in the pre-compression force, so that ball Good seal.
In summary, the key to solve the ball valve sealing structure sealing seat and seal seat material selection. Depending on the structure and use requirements, a reasonable choice seal seat of the structure, to ensure a good seal seat of the processing Gong Yi Xing; choose properties excellent, Shi Ying requirements of sealing materials used, Manzu valve sealing requirements, Tigaoqiufa the reliability of the And life, is the ball valve design should focus on consideration.