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Introduce a double block and bleed valve's structure and working principle.The valve is superior to common gate and ball valves in terms of its sealing performance and service life.The valve has the functions of being fireproof, on-line maintenance, double block and bleed, cavity pressure relief, internal leak detection and others. Illustrate the double block and bleed valve's functions and applications in the oil and gas storage and transportation systems in combination with examples, which has opened new development potential for process design of oil and gas storage and transportation systems and solved many problems encountered in pipeline design. It has not only optimized the pipeline design and improved the product quality but also saved the pipeline operation costs.
STRUCTURAL FEATURES
1. In the valve's opening/closing process, there is no contact between the sealing surfaces of the valve body and the vane, so the sealing surfaces suffer neither friction nor wear, contributing to the valve's long service life and small opening/ closing torque;
2. For the valve's maintenance, there is no need to remove the valve from the pipeline but just remove its bottom cover to replace the vane pair, thus very easy for the maintenance;
3. The valve's body and plug are reduced-bore or full-bore so that the medium can flow through the valve without any flow resistance, and it's also possible to clean the pipeline with pigging to overcome the shortcomings of the reduced bore valve;
4. The cavity of the full-bore/reduced-bore general valve is plated with hard chrome and the sealing area is hard and smooth;
5. The elastic seal on the vane is made of the fluorine rubber and molded and formed in a groove of the vane surface. The fireproof metal-to-metal seal is used as the backing of the elastic seal;
6. The valve is provided with an automatic bleed device [optional] which can prevent the abnormal pressure rise of the valve cavity and check the valve's effect after the valve is completely closed;
7. The valve's opening/closing indicator is in sync with the opening/closing position and can accurately display the gear drive full-bore general valve's opening/dosing status.
WORKING PRINCIPLE
The action of two sealing vanes mounted on the cock is the key to the working principle of the double block and bleed valve.
THE VALVE CLOSE
To close the valve, first rotate the hand wheel to rotate the cock and the sealing vanes by 90°; then the cock will move downwards; the moving cock drives the sealing vanes to the sealing surfaces of the valve cavity until the elastic gasket ring is uniformly pressed to the upper and lower ends of the valve bore to achieve sealing.
THE VALVE OPEN
To open the valve, first rotate the hand wheel to lift the cock and pull the sealing vane back from the sealing surfaces on both sides of the valve body. When the vane is completely retracted and separated from the sealing surface of the valve body, continue to turn the hand wheel to rotate the cock and the sealing vane by 90°, The valve is in the open position.
ABOUT SEALING
The elastic gasket ring is molded and formed in the groove of the vanes, and as the sealing vanes move to the valve's inlet and outlet, the gasket ring is also gradually pressed into the groove. The machined vane surface forms a secondary metal-to- metal seal with the valve cavity which can prevent the elastic gasket ring from being further pressed and also have a fireproof function.
DOUBLE BREAK AND BLEED VALVE AND RELEASE
This is a way to achieve complete containment of both ends of the pipeline with two block valves and one bleed valve in between. When the two main valves are closed, closing/opening the bleed valve can improve the system's safety. If the first valve leaks, the leaked medium can be led out by the opened bleed valve.
DOUBLE SEALING MODES
The two separate sealing vanes are compressed on upper and lower ends of the valve bore(double block], and when the valve is closed, the bleed valve will be opened to check the sealing effect(bleed].
TECHNICAL SPECIFICASTION
| Structural style | BB-BG |
| Driving mode | Wrench wheeLworm worm gear |
| Design standard | API6D |
| Structure length | ANSI B 16.10 |
| Connecting flange | ANSI B 16.5 |
| Test and inspection | API598 |
Main parts materials
