Structure and functional characteristics
The design and manufacture of high-pressure slab gate valves for anti high sulfur natural gas gathering and transportation projects are in accordance with API6D standards. The flow direction of the medium is unlimited. The key to its structural design is to ensure zero leakage sealing, and to obtain valve self-cleaning, self-relief in the middle cavity and fire prevention, anti static and other functions. See the Figure 1.
Figure 1 High-pressure slab gate valves dedicated anti high sulfur natural gas gathering and transportation projects
1. Discharge plug screws 2. Valve bodies 3. Seal rings 4. Valve seats 5. Valve wedges 6. Springs 7. Valve stems 8. Packing boxes 9. Metal sealing rings 10. Four opening rings 11. Packing spacers 12. Packing 13. Pressure plates 14. Bolts 15. Nuts 16. Brackets 17. Packing pressure plates 18. Dust covers
The structure of the valve wedge
The valve adopts a parallel single wedge with metal sealing structure, and the surface of the wedge is spray welded with hard alloys to ensure a reasonable thickness. Usually, it is not feasible to spray tungsten carbide on the wedge and the thickness should be more than 0.2mm as specified in the bidding, because the thickness of the sprayed layer being too thin will cause the sealing surface to be easily worn and not resistant to medium corrosion. The parallel single wedge has a diversion hole structure and adopts an operation mode with self-cleaning function. The slab gate valve is closed when the wedge is raised, and the gate valve is opened when the wedge is lowered. This kind of operation can make the dirt in the medium attach to the wedge hole and on the plane during the opening of the slab gate valve, and the dirt will be carried away by the medium flow, in stead of falling into the valve cavity in large quantities. At the same time, clogging and corrosion caused by the deposition of elemental sulfur in the medium are avoided.
The structure of the valve seat
The sealing surface of the valve seat adopts build up welding hard alloys, which is consistent with the sealing surface of the wedge to ensure a reasonable thickness. The structure design of the valve seat is flexible and can have characteristics of having different sealing. When the piston floating structure is adopted by the valve seat, a double sealing structure of O ring and wedge shaped sealing ring is adopted between the valve body and valve seat to ensure that impurities cannot enter behind the valve seat. At the same time, the use of wedge shaped sealing ring expands the application range of the elastic valve seat in the high temperature and high pressure area. There is a spring or disc spring structure behind the valve seat. In general, when the DN is smaller than 50, a disc spring is used. When the DN is bigger than or equal to 50, a spring is used. The anti sulfur valve seat does not have a grease injection port. This structure has a self relief function. When the pressure in the middle cavity is high, under the action of the medium in the middle cavity, the floating valve seat at the inlet end will be pressed to the direction of the valve seat groove to compress the spring, and the pressure in the middle cavity will be released to keep the valve cavity pressure in balance with the pipeline pressure at the inlet end. The sealing of the floating valve seat can realize the double functions of cutting off and release (DBB). When the valve seat adopts a non-piston fixed structure, an O ring seal is used between the valve body and the valve seat. Under the action of the medium, the wedge presses the valve seat to form a sealing specific pressure. The higher the pressure is, the better the sealing performance becomes. This structure requires high processing precision of the sealing surface of the wedge and valve seat, which is a single side forced seal. The fixed valve seat has a simpler structure in comparison with the elastic valve seat and the machining process is simplified, but it is not suitable for high-pressure slab gate valves for high sulfur natural gas gathering and transportation projects.
The design and manufacture of high-pressure slab gate valves for anti high sulfur natural gas gathering and transportation projects are in accordance with API6D standards. The flow direction of the medium is unlimited. The key to its structural design is to ensure zero leakage sealing, and to obtain valve self-cleaning, self-relief in the middle cavity and fire prevention, anti static and other functions. See the Figure 1.
Figure 1 High-pressure slab gate valves dedicated anti high sulfur natural gas gathering and transportation projects
1. Discharge plug screws 2. Valve bodies 3. Seal rings 4. Valve seats 5. Valve wedges 6. Springs 7. Valve stems 8. Packing boxes 9. Metal sealing rings 10. Four opening rings 11. Packing spacers 12. Packing 13. Pressure plates 14. Bolts 15. Nuts 16. Brackets 17. Packing pressure plates 18. Dust covers
The structure of the valve wedge
The valve adopts a parallel single wedge with metal sealing structure, and the surface of the wedge is spray welded with hard alloys to ensure a reasonable thickness. Usually, it is not feasible to spray tungsten carbide on the wedge and the thickness should be more than 0.2mm as specified in the bidding, because the thickness of the sprayed layer being too thin will cause the sealing surface to be easily worn and not resistant to medium corrosion. The parallel single wedge has a diversion hole structure and adopts an operation mode with self-cleaning function. The slab gate valve is closed when the wedge is raised, and the gate valve is opened when the wedge is lowered. This kind of operation can make the dirt in the medium attach to the wedge hole and on the plane during the opening of the slab gate valve, and the dirt will be carried away by the medium flow, in stead of falling into the valve cavity in large quantities. At the same time, clogging and corrosion caused by the deposition of elemental sulfur in the medium are avoided.
The structure of the valve seat
The sealing surface of the valve seat adopts build up welding hard alloys, which is consistent with the sealing surface of the wedge to ensure a reasonable thickness. The structure design of the valve seat is flexible and can have characteristics of having different sealing. When the piston floating structure is adopted by the valve seat, a double sealing structure of O ring and wedge shaped sealing ring is adopted between the valve body and valve seat to ensure that impurities cannot enter behind the valve seat. At the same time, the use of wedge shaped sealing ring expands the application range of the elastic valve seat in the high temperature and high pressure area. There is a spring or disc spring structure behind the valve seat. In general, when the DN is smaller than 50, a disc spring is used. When the DN is bigger than or equal to 50, a spring is used. The anti sulfur valve seat does not have a grease injection port. This structure has a self relief function. When the pressure in the middle cavity is high, under the action of the medium in the middle cavity, the floating valve seat at the inlet end will be pressed to the direction of the valve seat groove to compress the spring, and the pressure in the middle cavity will be released to keep the valve cavity pressure in balance with the pipeline pressure at the inlet end. The sealing of the floating valve seat can realize the double functions of cutting off and release (DBB). When the valve seat adopts a non-piston fixed structure, an O ring seal is used between the valve body and the valve seat. Under the action of the medium, the wedge presses the valve seat to form a sealing specific pressure. The higher the pressure is, the better the sealing performance becomes. This structure requires high processing precision of the sealing surface of the wedge and valve seat, which is a single side forced seal. The fixed valve seat has a simpler structure in comparison with the elastic valve seat and the machining process is simplified, but it is not suitable for high-pressure slab gate valves for high sulfur natural gas gathering and transportation projects.
Next: Classifications & Working Principles of Some Kinds of Gate Valves
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