One, the advantages of butterfly valve
1.convenient and rapid opening and closing, labor saving, small fluid resistance, can be often operated.
2.simple structure, small size, short structure length, small volume, light weight, suitable for large diameter valve.
3. It can transport mud and accumulate the least liquid at the pipe mouth.
4. Good sealing can be achieved under low pressure.
5. Good adjustment performance.
6. When fully open, the effective flow area of the valve seat channel is large and the fluid resistance is small.
7, the opening and closing torque is small, because the butterfly plate on both sides of the rotating shaft is basically equal by the medium, and the direction of the torque is opposite, so the opening and closing is less force.
8, sealing surface materials are generally rubber, plastic, so the low pressure sealing performance is good.
Two, butterfly valve shortcomings
1. the use of pressure and working temperature range is small.
2. the sealing is poor. Butterfly valve materials are polymer and metal, polymer seat is mainly suitable for low temperature conditions, metal seal seat butterfly valve can meet higher temperature and pressure conditions, but the elasticity of metal seat is lower than polymer seat, sealing performance is poor
3.The improvement of butterfly valve performance is closely related to its continuous improvement. In order to solve the extrusion problem of butterfly plate and seat of ordinary butterfly valve, a single eccentric butterfly valve is produced. Single eccentric butterfly valve stem centerline and sealing the centerline stagger, form the asymmetric structure, so as to not through the rubber lining sealing surface, caused the butterfly valve sealing surface to become a complete continuous circular arc surface, so for the sealing surface processing and manufacturing is very convenient, and disc and seat can also for grinding, for the butterfly valve sealing performance have sufficient guarantee. The upper and lower ends of the butterfly plate are no longer rotary axis, which reduces the excessive extrusion between the upper and lower ends of the butterfly plate and the seat, and can quickly leave the sealing surface and reduce the friction between the matching surface. However, due to the single eccentric structure in the entire switching process of the valve, the butterfly plate and seat scraping phenomenon has not disappeared, so it is not used much. The structure of the double eccentric butterfly valve is characterized by the shaft of the valve stem away from the center of the sealing surface of the seat, but also away from the pipeline and the center line of the valve. The effect of double eccentricity makes the valve open, the butterfly plate can quickly out of the seat, greatly eliminating the butterfly plate and the seat of unnecessary excessive extrusion and scraping phenomenon, reduce the opening torque, reduce wear, improve the life of the seat. The scratch is greatly reduced, but also makes the double eccentric butterfly valve can also use metal valve seat, improve the applicable temperature of butterfly valve, but because its sealing principle belongs to the position sealing structure, that is, the butterfly plate and the sealing surface of the valve seat for line contact, through the butterfly plate extrusion valve seat caused by elastic deformation, sealing effect, Therefore, the closing position is very demanding (especially the metal seat), the bearing capacity is low, and the friction phenomenon of the butterfly plate or valve body sealing surface is very serious.
Triple Offset butterfly valve is in the double eccentric stem axis position eccentric at the same time, coupled with the conical sealing surface center line relative to the center line of the valve deflection Angle, forming a third eccentric. The circumference of the sealing line of the seat increases with the increase of the Angle eccentricity. When the seat is worn and damaged, the sealing effect can be achieved again by changing the closing valve position in the closing direction, that is, the elastic compression of the Angle eccentricity and the seat is increased. Through the butterfly plate valve seat opening and closing running, eliminate the damage of the valve seat, and the use of the floating valve seat can ensure the best sealing position between the butterfly plate and the valve seat after the change of the closing valve position. The third eccentricity can make the valve seat and the butterfly plate in the entire stroke of the valve completely detached, butterfly plate and the valve seat contact is only in the sealing moment, so it greatly reduces the friction between the valve seat and the butterfly plate in the switching process, reduces the wear, prolongs the service life. Because the sealing is achieved by the extrusion between the valve seat and the seal ring on the butterfly plate, the sealing pressure can be applied by the stem torque, if the valve structure design is reasonable, it can achieve a very high sealing effect. The reasonable design of the third eccentricity can eliminate the possibility of the valve sticking, thus improving the reliability of operation. Compared with the general butterfly valve, three eccentric butterfly valve usually uses metal hard seal seat, to solve the problem of high temperature resistance. A MULTI-layer sealing ring made of stainless steel sheet and graphite sheet is installed around the butterfly plate, which has the dual advantages of metal hard seal and flexible soft seal, and solves the leakage problem. Three eccentric butterfly valve as a high performance valve, with its unique structural characteristics and performance advantages become the first choice in the regulator market.
