Main structural forms of safety valves

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Main structural types of safety valves and their structural characteristics: 1. Safety valves without an adjusting ring have a proportional response characteristic in terms of their operation. 2. Safety valves with an adjusting ring also have a proportional response characteristic in terms of their operation. The discharge pressure and the opening/closing pressure difference can be adjusted using the adjusting ring. The fully open safety valve, which features a rebound disc and an adjusting ring, uses the rebound disc to redirect the flowing gas, thereby generating greater lift on the valve disc and enabling it to reach its fully open position. The discharge pressure and the opening/closing pressure difference can be adjusted using the adjustment ring. Its operating characteristic is a two-stage type; the 4-port jet valve utilizes a recoil disc to redirect the ejected airflow, thereby generating greater lift on the valve disc and achieving full opening. The discharge pressure and the opening/closing pressure difference can be adjusted using the adjustment ring. Its operating characteristic is two-stage action. A jet tube is also provided; the suction effect of the exhaust airflow is utilized to reduce the pressure in the chamber above the valve disc, thereby assisting in the opening of the valve and generating greater lift. The fully open safety valve with dual adjustment rings features one adjustment ring each on the guide sleeve and the valve seat (referred to as the upper and lower adjustment rings). The lower adjusting ring is mainly used to adjust the discharge pressure, while the upper adjusting ring is used to adjust the opening/closing pressure difference. The safety valve with backpressure control sleeve, in addition to having upper and lower adjusting rings, also features a backpressure control sleeve on its valve stem. When the valve is opened, the control sleeve rises along with the valve stem; the area of the annular channel between the outer conical surface of the control sleeve and the valve body increases, which reduces the back pressure in the chamber above the valve disc, thereby facilitating the opening of the valve ； When the valve is closed, the control sleeve descends, reducing the area of the annular channel between it and the valve body. This increases the back pressure in the chamber above the valve disc, helping to push the valve back into its closed position. Structural features: 7. Bellows-type back-pressure balanced safety valves – The effective diameter of the bellows is equal to the average diameter of the sealing surface of the closing element; the additional back pressure on the valve disc is zero, so any changes in this additional back pressure do not affect the valve’s opening pressure. 8. Diaphragm-type safety valves – These valves utilize two chambers, separating the spring from the medium that is discharged, thereby protecting the spring from coming into contact with corrosive substances. 9. Safety valves with cooling sleeves – The inclusion of cooling sleeves helps to reduce the temperature in the spring chamber and prevents the discharged medium from directly eroding the spring. Suitable for high-temperature applications. The disc of a balanced safety valve is subjected to the pressure of the medium in both upward and downward directions; the spring load depends only on the difference between the forces exerted by the medium in these two directions. This allows for the use of a smaller spring in high-pressure situations. The medium acts on the periphery of the valve disc, while the element that bears the pressure of the medium is a diaphragm (or possibly a piston or bellows) whose area is much larger than that of the valve disc’s sealing surface. This amplifies the force exerted by the medium, thereby increasing the pressure on the sealing surface, enhancing the sealing performance, and improving the sensitivity of the valve’s operation. Internal-mounted safety valves are used in liquefied gas tankers. Due to the limitations on the size of the part of the valve that extends outside the liquefied gas tank, a portion of the valve must be placed inside the tank. The force exerted by the weight of the lever-type safety valve is amplified through the lever and then applied to the valve disc. The magnitude of the load remains constant during the opening and closing of the valve. This type of valve is sensitive to vibrations and has poor return-to-seat performance. It is one of the pilot-operated safety valves; it operates under infinite load conditions: the closing force acting on the main valve disc is provided by the pressure of the working medium, and this force is not limited. The main valve cannot open before the pilot valve acts to load the driving piston of the main valve. Its advantage is good sealing performance of the main valve. Structural features: This is the second type of pilot-operated safety valve; it is a valve with a limited load capacity – the closing force applied to the main valve’s disc is provided by a spring, and its magnitude is restricted. Even if the pilot valve fails to function, the main valve can still open within the allowable overpressure range. Its disadvantage is that the sealing performance of the main valve is not as good as that of the 16-pilot safety valve (a type of pilot-operated safety valve without flow regulation). Structural feature: the pilot valve has no flow regulation mechanism ； Can operate without leakage at a pressure very close to the set value ； Polytetrafluoroethylene soft sealing material is used ； The valve operates properly without being affected by back pressure, and no bellows are required ； The operating pressure can be set during use, making it easy to adjust ； The nominal pressure rating can reach 10,000 lbf/in2 ； The set pressure range is 0.1 to 25 MPa. Working principle: When the system pressure is lower than the set pressure of the valve, the medium pressure enters the main valve’s pressure chamber through the seal on the pilot valve, acting on the main valve disc and generating a downward force that closes the main valve ； As the system pressure rises and approaches the set pressure, the pilot valve piston moves upward, causing the upper seal to close; at this point, the lower seal of the pilot valve remains closed as well. The system pressure increases slightly, the lower seal opens slightly, and the pressure in the main valve’s pressure chamber is released through the exhaust port controlled by the pilot valve ； When the system pressure reaches and slightly exceeds the set pressure, the lower seal of the pilot valve opens to release the excess pressure, which in turn causes the pilot valve piston to move downward. This feedback mechanism allows the main valve disc to remain in a certain position, thereby achieving a regulating effect ； When the system pressure exceeds the limit, the main valve disc opens fully ； When the system pressure drops below the set value, the seal beneath the pilot valve closes. Further reduce the pressure until the pressure in the return chamber is restored; then close main valve 17. Pilot-operated breathing valve: The valve disc of this breathing valve is supported by an air chamber made of a diaphragm with a larger diameter. Before the exhaust valve opens, a compression force several times greater than the lifting force is maintained, ensuring reliable sealing ； The pilot valve provides precise pressure protection ； The opening and closing pressure difference can be adjusted by the pilot valve ； The set pressure remains stable, unaffected by back pressure ； With the pilot valve disc fully open, the displacement is ensured ； The valve body and sealing materials can be selected based on the temperature of the medium. The gravity-type safety valve features a dual-sealing structure (sponge rubber gasket and O-ring), which ensures reliable low-pressure sealing and reduces the risk of material loss or contamination ； Gravity-type valve disc, simple structure, easy to maintain ； Stainless steel interior components, corrosion-resistant and reliable in operation ； The valve body and the soft-sealing material can have properties selected based on the medium and temperature: the inlet flange of the exhaust valve and the outlet flange of the suction valve are connected together to form a breather valve