A safety valve is an automatic valve that uses the medium's own force to expel an additional amount of fluid without any external force to avoid the pressure exceeding the additional safety value. When the pressure has recovered to normal, the valve closes again and prevents the continuous flow of the medium. (TSG ZF001-2006) safety valves are mainly used in boilers, pressure vessels and pipeline equipment to ensure that the system does not cause accidents due to excessive pressure, and plays an important role in protecting the operation of equipment and the safety of operators.
The tension spring of the safety valve should meet the following requirements:
1. It is advisable to use cylindrical spiral tightening tension springs;
2. The structure of the safety valve can avoid the direct erosion of the tension spring by the discharged medium, especially the hot corrosive fluid;
3. The tension spring design can ensure that when the safety valve is fully open, the deformation of the tension spring is equal to 20% - 80% of the large deformation of the tension spring, and the large shear stress of the tension spring design is not greater than 80% of the allowable shear stress.
In order to ensure the stability of the tension spring during long-term operation, the tension spring should be subjected to strong pressure treatment, and a strong pressure treatment statement should be provided, and the result should meet the following requirements:
1. The tension spring is pressed from the free height to the height of the parallel circle at room temperature, and the remaining deformation of the free height is detected for 10 min, which shall not be greater than 0.5% of the free height;
2. For the tension spring of the same standard and the same heat treatment furnace, the deformation (or stiffness) under the specified load shall be determined, and the error shall not be greater than 10%, and the tension spring production unit shall provide the functional statement test of the tension spring and the heat treatment statement and qualification of the same standard and heat treatment furnace with the same standard. After receiving the tension spring, the safety valve manufacturer checks the raw material statement and downloads the relevant raw material standards, tests the scale, raw materials, and checks the furnace batch number. The raw material statement includes the raw material certificate, heat treatment records, strong pressure treatment records, and strong pressure test records of the tension spring. After receiving the tension spring, the safety valve manufacturer needs to re-inspect the scale, stiffness coefficient and deformation in accordance with the requirements of the national standard, and the test statement should include the load, deflection, R value, free length, compressed length and other data of the tension spring. The tension spring can be installed on the safety valve only after passing the acceptance of the factory.
There are three main types of safety valve structures: tension spring type, lever type and pilot operated type. Tension spring type refers to the sealing of the valve disc and the valve seat by the effect force of the tension spring; The lever type relies on the effect of the lever and the hammer; The pilot operated safety valve is a pulse safety valve designed to meet the needs of large volumes, consisting of a primary safety valve and an auxiliary valve. When the medium pressure in the pipeline exceeds the specified pressure value, the auxiliary valve is opened first, and the medium enters the main safety valve along the conduit, and the main safety valve is turned over, so that the increased medium pressure is reduced. There are many different classification methods for safety valves according to their different conditions, such as structure, open method, discharge method, effect principle, etc
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