Reasonable selection of safety valves is the key to ensuring the safe operation
Release time：2018-09-05 Browse：504
Safety valves are confused with other safety equipment. Many people think that there is a pressure gauge on the pressure vessel, and there is no need to install a safety valve. As we all know, the pressure gauge can only indicate the pressure value, and can not play the role of overpressure protection. Electrical automatic protection devices cannot completely replace safety valves because they will lose their function in the event of power failure or line failure.
Safety valve is an automatic valve, with a shut-off valve that needs to be manually opened and closed, drainingThe valve is different. In the case of overpressure of the pressure equipment, it can automatically open, vent the excess medium, ensure the safety of the equipment, when the pressure drops to the specified value, it can automatically close and restore the seal. Therefore, the safety valve is one of the most basic mechanical protection devices. According to the relevant regulations, a safety valve must be installed on the pressure vessel, otherwise the safety of the pressure vessel is difficult to guarantee.
Conceptual misunderstanding may cause safety hazards Many people are unclear about the various "pressure" concepts of safety valves, so that they are purchasing, Difficulties arise when using safety valves, which poses a safety hazard.
The "pressure" in the safety valve specification is: nominal pressure and working pressure. The nominal pressure refers to the maximum service pressure of the safety valve at the specified lower than 200 ° C. It is an important basis for the normal temperature hydraulic pressure test. Its code is PN, the unit is MPa. When the safety valve operating temperature rises, due to the material As the temperature increases, the strength decreases. The actual allowable working pressure decreases with increasing temperature. All valve products must follow the principle of temperature rise and pressure reduction. The country has strict regulations. The division of the nominal pressure grade is formulated with reference to the classification of pressure vessels in China.
In addition to ensuring the opening pressure value, the safety valve also requires the discharge pressure, opening height, and return pressure to meet the specified requirements. In order to ensure the operational characteristics of the safety valve, each spring can only work within a certain pressure range, which is the pressure level of the safety valve, where the pressure level refers to the opening pressure range. Therefore, springs of different pressure levels are selected within different opening pressure ranges of the safety valve. If the safety valve is ordered at the nominal pressure value without the pressure level, the spring pressure level range is incorrect, cannot be used, and has to be replaced, which not only delays production but also increases unnecessary expenses. In addition, considering the factors such as oxidative peeling and thinning of the spring during heat treatment, the upper limit should be biased when the pressure level is selected.
Selecting the safety valve according to the conditions of use first needs to know what equipment, what medium, working temperature, how much pressure is opened, and how much discharge capacity is required. Safe, reliable and economical are the main principles. Steam system, non-enclosed full-open safety valve with wrench; small medium for liquid medium and gas volume, micro-open safety valve; high temperature medium, safety valve with radiator; flammable, toxic medium, closed Safety valve. The model and specification of the safety valve are determined according to JB308-75. It fully reflects the valve connection mode, structure type, nominal pressure, valve body and sealing surface material. Knowing how to make a regular valve model, the user can know if the valve selected meets the requirements. The specifications of the safety valve are divided according to the inlet diameter and are indicated by DN. According to the working temperature, medium, opening pressure and discharge amount and the rated displacement coefficient, the diameter of the flow channel and the nominal diameter can be determined. The diameter of the valve is determined according to JB79-59 regulations, such as DN40, DN50, DN65, DN80, DN100. Pay attention to the safety valve of the same specification. The outlet diameter is different depending on the model. The size of the inlet and outlet of the micro-opening safety valve is the same. The full-opening safety valve has a larger outlet diameter than the inlet diameter due to gas expansion.
