Elastic Seated Eccentric Cylindrical Plug Valves

1. Structural forms
An elastic seated eccentric cylindrical plug valve is a new type of plug valve (Figure 5), which adopts an elastic seated eccentric structure. The plug is of crankshaft type, and the surface is completely covered with rubber. The valve seat is surfaced with corrosion-resistant alloy. There is a certain eccentric distance from the center of the plug’s sealing surface. The cross-section of the flow channel is rectangular.
 

Figure 5 Eccentric plug valves

1. Valve bodies 2. Plugs 3. Thrust washers 4. Bonnets 5. Packing 6. Gaskets 7. Glands 8. Brackets 9. Worm gears

 
2. Working principles
With this kind of elastic seated eccentric structure, the crankshaft cock not only has enough strength to withstand high pressure and transmit torque, but also can skillfully avoid the flow channel when the valve is fully open to obtain a large flow area. The surface-coated with rubber and the forming process of hot vulcanization molding is adopted, which ensures the firm adhesion between the rubber and the internal metal skeleton, the smooth outer surface, and the accurate sealing surface size, which improves the corrosion resistance and service life of the valve, and the reliability and interaction of the seal. A corrosion-resistant alloy surfacing welding seat is adopted and the sealing surface contact area is small; there is a certain eccentric distance from the center of the cock sealing surface, ensuring zero leakage of the seal, reducing the operating torque of the valve opening and closing, and prolonging the service life. Rectangular flow cross-section can obtain ideal linear regulation when the valve is used in a regulating device.
 
The closing and opening of the elastic seated eccentric plug valve are realized by the eccentric movement of the plug and valve body. The plug has an eccentric distance relative to the valve body, and the valve seat on the valve body also has an eccentric distance relative to the center of rotation of the cock body. When the cock body rotates 90° from a fully open to a fully closed position, the sealing surface of the plug body will fit the valve seat to close the valve and achieve the purpose of sealing. When the valve is in the open position, the entire plug body leaves the channel, and the full flow of fluid passes through. At this time, the flow capacity is the largest and the flow resistance is the smallest. When the valve is in the regulating position, a part of the plug blocks the channel, and the flow area changes, so that the flow is regulated. The plug does not contact the valve seat or the valve body when it rotates due to the eccentric movement, so there is no abrasion and no jamming. This feature is especially suitable as an automatic control valve. When the valve is in the closed position, the plug and the valve seat are in contact, and the sealing specific pressure between the plug and the valve seat increases with the increase in the input torque and medium pressure, and the sealing reliability is greatly improved.

 
Figure 6 Working principles

3. Characteristics of performance 
The elastic seated eccentric plug valve has made many improvements to the traditional plug valve and hemispherical valve to ensure the reliable function of the product. From the following characteristics of performance, we can understand the advanced function and structural design of the valve.
 

The sealing structure formed by the elastic plug and the corrosion-resistant valve seat ensures reliable sealing of the valve and zero leakage. It overcomes the defect that the metal seal of the traditional plug valve and the hemispherical valve is easy to leak.

Eccentric seal

The operating force only acts on the very short stroke when the sealing surface of the valve contacts or separates, and it decreases rapidly with the decrease in the working pressure; the sealing surface can be automatically compensated without wear. It solves the problem that traditional plug valves and ball valves require a great and lasting operating force and the sealing surface is severely worn due to the forced extrusion of the sealing surface during the full stroke.
 

The integral cocks of all sizes adopt the latest vulcanization process, and the outer surface is completely covered with high-performance rubber, which has good sealing elasticity and is resistant to fluid corrosion and high-speed fluid erosion. It overcomes the defect that the exposed metal cock of the traditional plug valve and the separated ball core of the hemispherical valve are susceptible to fluid corrosion.
 

The stainless steel or pure nickel surfacing valve seat is firmly combined with the valve body, which is resistant to the wear of solid particles, damage to corrosive media and the erosion of high-speed fluid. The interchangeability of the seal is good, and it can continue to be used only by replacing the valve cock. It overcomes the shortcomings of poor interchangeability of the floating seat sealing part of the hemispherical valve and difficult maintenance in the later period.
  

Straight-through flow channel has a small loss of fluid head. The rectangular cross-section can be used as manual, electric and pneumatic control valves, and the flow linear adjustment is very good. It overcomes the problem of unsatisfactory linear regulation of the circular cross-section when traditional ball valves and hemispherical valves are used as regulating valves.

One-piece bow-shaped valve shafts 

The valve shaft and the cock are integrally casted, with high transmission strength and good rigidity. The bow-shaped valve shaft can avoid the flow channel when the valve is fully opened, and the diversion effect is remarkable. It is lighter than traditional plug valves and hemispherical valves.

Removable valve bonnets

The valve bonnet and the valve body are connected by bolts, and the valve can be maintained on the pipeline only by removing the valve bonnet bolts. The traditional ball valve is a split or cylindrical valve body. When the valve fails, the whole valve must be removed from the pipeline for maintenance.
 

The valve body, bonnet and other pressure shells are made from high-strength ductile iron, which has high-pressure strength and good rigidity, and is lighter than gray cast iron traditional plug valves and hemispherical valves, and convenient for transportation and hoisting. At the same time, as the surfacing welding matrix of the sealing surface, it has good manufacturability in combination with the surfacing welding material of the sealing surface.

High-speed media

High-performance ductile iron shells, sealing rubber and overlay welding seats are suitable for scouring high-speed fluid. The working temperature of the medium can reach -50 to 135℃, especially suitable for various cold and hot water.

Corrosion-resistant surface treatment 

According to the corrosiveness of the medium and the working environment, the corresponding surface anti-corrosion treatment scheme can be flexibly selected to ensure a long service life under various harsh working conditions.