Dual-seal track valve

Ah, track valves can also have double sealing. Are there any diagrams? I’d like to ask about the principle, thank you~~~ Ball valves excel in preventing blockages and also offer good sealing performance under pressure differences, but I’m not sure how dual sealing is achieved~~~

Could you explain the principle and the conditions of use?

Dual-seal track valves do require some technical expertise. Are they also expensive? What’s the price? Could the original poster provide information on their performance and price? Thanks

It is recommended that the original poster upload the relevant images online; it’s more convenient to discuss while sharing them! ! ! ! :handshake :victory:

Overview of the handwheel-driven double-seal guide rail valve TG4X: The TG4X type handwheel-driven double-seal guide rail valve is a new type of valve that our company has successfully developed through its own design efforts, drawing on advanced technologies from around the world. This valve features optimal dual-shutoff and venting functions, enabling complete shutdown of the pipeline. It is widely used in crude oil and other product pipelines, refineries, metering systems, the petrochemical industry, liquefied petroleum gas pipelines, **facilities, marine transportation, and other fields. Operation principle and structure description: The opening or closing of the double-seal guide rail valve is achieved through the radial movement of the valve disc as well as 90-degree rotation to the left and right. It turns on when rotating left (counterclockwise) and turns off when rotating right (clockwise). To operate a valve with a handwheel, it generally requires 4 to 6 turns to open or close it. The valve is open when its indicator is parallel to the pipeline axis, and closed when it is perpendicular to the axis.

The dual-seal structure of the double-seal plug valve is not only reflected in the two valve discs; more importantly, each valve disc’s sealing surface features both soft and hard sealing elements. The hard seal serves to protect the soft seal, which not only ensures zero leakage from the valve but also endows it with fire-resistant properties. As shown in Figure 2, Figure a depicts the shape of the soft seal in the open state ； Figure b shows the shape of the soft seal in the closed state. As can be seen from the diagram, the soft seal (rubber) is embedded in the groove of the valve disc, with a protrusion in the middle and recesses on both sides ； This facilitates the compression of the soft seal during the closing process, allowing it to flow into the grooves on both sides, thereby ultimately forming a hard seal ； Its advantage is that it protects the soft seal from being damaged, while ensuring the implementation of the hard seal. The excellent sealing performance of the double-seal valve ensures stable operation of the pump and prevents the occurrence of \"air blocking flow,\" a fact that has been confirmed by users on numerous occasions. The greatest advantage is its long service life and very low maintenance rate. Figure 2: Sealing type. 2. Fixing of the soft seal: The soft seal is formed using a molding and vulcanization process; nitrile rubber is vulcanized once, while fluororubber is vulcanized twice ； Firmly embedded, it will never fall off. 3. Leak prevention design: In addition to the O-ring seals between the valve end cover and the valve body, as well as between the bottom plate and the middle flange of the valve body, flexible graphite gaskets are also used between the contacting surfaces, thereby achieving double-layer sealing. Figure 3 shows the leak prevention design ； In addition to the flexible graphite packing in the valve stem section, an O-ring seal is also added at the part where the packing gland meets the valve stem and the end cap ； The connection between the pressure relief section and the discharge plug and the valve body section is designed with tapered pipe threads, and sealed with copper gaskets. All these measures effectively ensure the reliability of sealing and prevent any external leakage (as shown in Figure 3). 4. It features dual shutdown and discharge functions: This is a method for preventing two different fluids in the pipeline from mixing with each other. The traditional process design is shown in Figure 4a: the medium is isolated using two isolation valves (gate valves or ball valves), and a drain valve is installed between these two isolation valves ； When the isolation valve experiences internal leakage, the leaking fluid will be discharged through the relief valve, without passing through the other isolation valve and causing mixing of the two fluids. If a double-sealed plug valve is used, only one valve is required to achieve the aforementioned functions. As shown in Figure 4b, the bottom of the double-sealed guide rail valve has a drain plug; this plug is removed once the valve is closed ； If internal leakage occurs in one of the valve petals, the leaking fluid is discharged through the plug hole, thereby preventing the mixing of the two fluids. Another important function of the drain plug is to remove waste and water: when the medium is dirty, sediment can be regularly removed through the drain plug ； Before freezing weather arrives, the water accumulated in the interior can be drained through the drain plug to prevent the valve from being damaged by freezing. Figure 4: Principle of dual shutdown and drainage functions. 5. Online maintenance capability: When the soft seal is damaged due to impurities or other reasons, or when the actuator malfunctions, it is possible to carry out repairs or replacements without removing the valve from the pipeline, with the entire process taking no more than 1 hour. 6. Function for detecting internal leakage: It is possible to determine whether the main seal ensures zero leakage by using the needle valve 1 of the \"pressure relief system\"; for more details, see \"7. Internal chamber pressure relief function\". 7. Medium-chamber pressure relief function: The API 6D standard stipulates that \"for all double-sealed valves, when used in liquid media, they must have a pressure differential relief function,\" with the pressure differential resulting from changes in ambient temperature. In the normally closed state of a double-seal valve, the pressure in the middle chamber increases rapidly as the temperature rises ； If this pressure difference is not relieved in a timely manner, it will have a serious impact on the operation of the valve, and may even cause the valve body to burst. Manually operated double-seal plug valves usually come with two pressure relief systems to choose from: 1) Manual pressure relief system: typically a needle valve installed on the end cover, as shown in Figure 1. Such a pressure relief system is generally installed when the medium is a liquid that can be discharged in small amounts into the atmosphere. When the valve is in its normally closed state, after closing the valve, open the needle valve (at this point, it is also possible to check for any internal leakage in the valve) ； Remember to close the needle valve before reopening the valve. 2) Differential thermal pressure relief system: It is a piping system equipped with a check valve, as shown in Figure 5. In the diagram, needle valve 1, tee 1, check valve 1, tee 2, and needle valve 3 form a differential thermal pressure relief system ； Pin valve 1 is normally closed, and pin valve 3 is normally open. When the medium is a liquid that cannot be discharged into the atmosphere, such a pressure relief system is required, generally to relieve pressure in the upstream pipeline (on the side with the medium). This type of pressure relief system does not require manual control; the needle valve 1 is manually opened only when it is necessary to detect internal leaks. Figure 5 shows a comprehensive diagram of the thermocouple-based pressure relief and pipeline pressure reduction systems. It should be noted that the needle valves and check valves in the pressure relief system are subject to extremely strict design requirements; both soft and hard sealing types must be used to ensure zero leakage during installation. The configuration of the pressure relief system is generally determined by the manufacturer in accordance with standards, based on the medium used and the operating environment. Users may submit requests, but these must not violate the standards. 8. Valve operating mechanism and self-locking property: The valve operating mechanism features a unique “L”-shaped groove structure (as shown in Figure 6a), which separates the axial linear movement of the valve core from its 90° rotational movement, thereby enabling flexible and easy operation of the valve. In the diagram, A→B represents the linear moving part, with the groove serving as a guide ； B→C is the 90° rotation section, with point C serving as the limit point ； For valves operated by hand wheels, there is a recess at point C; this recess works in conjunction with the stop pin of the limit shaft portion (see Figure 1) to enhance the self-locking property of the valve ； For valves driven by worm gears, the driving mechanism itself has good self-locking properties, which means that there is no stop pin in the limit shaft section. Additionally, for valves with this type of structure, in order to reduce the number of rotations required to turn the handwheel, the trapezoidal thread between the shaft sleeve and the main shaft typically has 4 to 8 threads (depending on the specifications). Figure 6: Design of the guide groove. It should be noted that among similar valves available on the market today, the design of the guide groove is as shown in Figure 6b; this shape resembles an “S”-shaped helix on the cylindrical surface of the shaft sleeve. The operating principle is that A→B represents the initial linear movement phase of the valve core ； During the B→C process, the valve spool undergoes both linear and rotational motion; therefore, the guide pin must withstand greater shear forces, which imposes higher requirements on its strength ； At the same time, the valve spool needs to be designed with a larger stroke; otherwise, friction between the soft seal and the inner wall of the valve body is likely to occur, increasing the operating force. The double-seal guide rail valve states that it “does not use an S-shaped helical structure”. 9. Accurate and intuitive status indicator: As shown in Figure 1 under “1. Indicator tag”, when the indicator tag is parallel to the axial direction of the pipeline, it indicates that the valve is in the open position ； When perpendicular to the axis, it indicates that the valve is closed. 10. Installation: The installation of the double-seal valve is not restricted by spatial orientation; it can be installed horizontally, vertically, or in any other direction. IV. Unique Features of the Product 1. Material Selection: The spindle of the manipulator is typically made of treated stainless steel (2Cr13), while the bushings are made of high-quality alloy steel and undergo nitriding treatment to ensure long service life; other components such as pins are also subjected to special treatments.