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Technical Characteristics Analysis of Metal Plane Seal Pneumatic Butterfly Valve
1 Foreword In recent years, with the development of modern industry, the use of butterfly valves has expanded from low pressure water supply to media with temperature higher than 538 ℃ and low to -184 ℃. The pressure is also from low to high, which is widely used in air separation, chemical industry , Metallurgy, sewage treatment and other fields. And the growing caliber, higher performance requirements, longer service life requirements. At present, most of the butterfly valves produced at home and abroad are rubber seals and plastic seals, which are easily worn and aged and fail to reach the continuous operation cycle of the equipment. Taking the air separation as an example, in today's air separation plant mainly based on cryogenic separation principle, the process adopts a molecular sieve pre-purification process, the working pressure is 0.5 to 0.9 MPa, the medium temperature varies from 10 to 200 ° C., and the switching valve is used Large temperature, large caliber, switching frequently, the valve rubber seal is easy to wear and aging, and replacement is more difficult. In response to these circumstances, developed a series of enhanced metal piston seal pneumatic butterfly valve series. This new type of butterfly valve has obtained national practical patent (patent number: z.3). 2 metal seal pneumatic butterfly valve features (1) the use of lever-type opening and closing structure, so that the relative seal between the relatively small slide, reducing the relative wear and tear. (2) The implementing agency uses the connecting rod augment mechanism. This mechanism in the butterfly valve is closed, the drive can output the maximum torque, and has self-locking performance, safe and reliable. (3) the use of metal seal structure, with strong corrosion resistance and wear resistance, suitable for high temperature environment, long service life. (4) The key components were optimized, so that the total number of valve opening and closing can reach 1 × 106 times or more. (5) The valve control system uses non-contact electromagnetic reed switch, not subject to environmental conditions, and the signal sensitivity, high accuracy, remote remote control, pneumatic control and automatic control, and equipment can also be achieved without supporting People operate. 3 Structure and working principle 3.1 Lever type opening and closing structure Lever type opening and closing structure. When the butterfly valve is closed, the spindle and the lever taper pin fastened, counterclockwise around the o-point rotation, the lever with a hole pin drive disc ab, driven by the compression spring disc fixed to the fulcrum n of the lever, with the spindle lever Rotate and turn. When the butterfly valve b and the upper end of the sealing surface all the contacts to seal. The opening process is the opposite. In the opening and closing process, the seal relative sliding between the small, reducing the relative wear and tear. In the closed state for the axial pressure seal, changing the traditional external force squeeze seal. 3.2 Connecting rod force type actuator Connecting rod force type actuator, the piston moves to the right under the action of air pressure, the piston rod carries the power arm to slide in the box, the connecting rod affects the rocker to rotate clockwise to output the torque. The connecting rod and rocker length (h) the same, are equal to the tank slot heart to the output center distance. According to the analysis of force, we can see that p = q / cosαα = sin-1 (1-sinβ) m = phcos (90-α-β) = qhsin (α + β) / cos (α + β) It can be seen from the above equation that the β angle decreases, the α angle increases, and the m torque value increases accordingly. When β = 0 °, α = 90 ° (the butterfly valve is closed), the drive outputs the maximum torque while the torque during opening and closing is small. This feature in the curve just inclusive of the butterfly valve operating torque curve to meet the butterfly valve in the closed or open state required sealing torque. 3.3 Flat seal structure Pneumatic butterfly valve sealing the past, the general use of spherical seals, sealing pressure is the radial extrusion force, the sealing interference can not be adjusted, the sealing performance depends on the amount of sealing material interference, therefore, the choice of design Sealing materials and the amount of interference is very important. In the work, especially in the molecular sieve pre-purification process, the switching valve work in the 10 ~ 200 ℃ range, the rubber ring, the rubber linear expansion coefficient is large, affected by temperature changes, the amount of interference is difficult to accurately determine. If the interference is large, not only increase the friction, and often appear "bite the edge" and "tongue" phenomenon, so that the seal failure, a small amount of interference leakage occurs. Even if the choice of interference reasonable, and this frequent valve switching, after a period of operation will wear out due to wear and tear. If using non-rubber sealing materials, as far as we know from the present information, their elastic deformation is very small, radial sealing interference is difficult to control, manufacturing is quite complicated and the cost is very high. At the same time the rubber seal material, the temperature changes, the rubber seal ring due to fatigue damage caused by premature aging, for large air separation plant equipped with large-diameter pneumatic butterfly valve, the replacement of the seal is very difficult. The new sealed pneumatic butterfly valve is the use of metal seal structure, the valve as a non-wearing parts made of stainless steel surfacing carbide, seat ring sealing ring made of copper-based alloy or stainless steel welding cobalt alloy, they have strong corrosion resistance and Wear resistance, the use of temperature range, long-term use between -40 ~ 300 ℃, therefore, the service life is much larger than the rubber seal. Because the movement of the valve plate adopts the lever form, when the valve plate is closed, the valve plate and the valve seat become a plane contact seal, then the lever is equivalent to the cam mechanism. If the main shaft continues to rotate, the valve plate continues to shift forward to balance the force , The working medium pressure, but also to achieve self-sealing, to ensure the reliability of the seal. When the entire sealing surface wear, but also has automatic compensation for seal wear characteristics, thereby extending the service life. Due to the rational structure of the valve, its performance is better than other domestic valves, has been able to replace similar foreign products.