How the safety valve eliminates malfunctions and routine maintenance and inspect
Release time：2018-09-17 Browse：769
I. Safety valve is an important safety accessory for pressure-bearing special equipment
Safety valve is an automatic valve that uses the force of the medium itself to discharge a nominal amount of fluid without any external force to prevent pressure from exceeding Rated safety value. When the pressure returns to normal, the valve closes again and prevents the media from continuing to flow out. The safety valve is an important safety accessory for pressure-bearing special equipment such as boilers, pressure vessels and pressure pipes. It is a safety device designed to prevent explosions caused by excessive pressure in abnormal conditions. The safety and economy of the equipment are important. Both play a major role. Therefore, the State Council of the People's Republic of China Order No. 549 "Special Equipment Safety Supervision Regulations", "Pressure Vessel Safety Technical Supervision Regulations", "Safety Valve Safety Technical Supervision Regulations" and related safety technical specifications, strict requirements for special equipment in use The safety valve is regularly calibrated, and the periodic inspection period is generally at least once a year, so as to better ensure the validity and timeliness of the safety valve periodic calibration.
On May 8, 2009, the State Administration of Quality Supervision issued the revised Regulation No. 1 of the Safety Regulations for Safety Valves, on Safety Valves. The design, manufacture, inspection, installation, use, calibration and maintenance processes are advanced, practical, and consistent with existing procedures and management practices, and comply with and comply with the requirements of the Special Equipment Safety Supervision Regulations. It also ensures the safe use of safety valves on pressure-bearing equipment such as boilers, pressure vessels and pressure pipes.
Second, the contents on the nameplate of the safety valve
On the safety valve nameplate or on the outer surface of the safety valve, there are at least the following signs: safety valve manufacturing license number and logo, manufacturing unit name, Safety valve structure type, date of manufacture and its product number, nominal pressure (pressure level), nominal diameter, runner diameter or runner area, setting pressure, valve body material, rated displacement coefficient or rated for a certain fluid Displacement.
The nameplate should be made of corrosion-resistant material and must be securely attached to the outer surface of the valve body or bonnet.
Three, common faults and elimination methods for safety valves
Safety valve failures are primarily due to improper design, manufacture, selection, or use. If these faults are not eliminated in time, it will affect the efficacy and life of the safety valve, and even fail to provide safety protection. Personnel engaged in the operation and maintenance, disassembly inspection and inspection of safety valves in use shall obtain the "Special Equipment Operation Personnel Certificate". Common faults and elimination methods are as follows:
(1) Leakage. Under the normal working pressure of the equipment, leakage between the valve disc and the seat sealing surface exceeds the allowable degree. The reason is that there is dirt between the valve flap and the valve seat sealing direction. The valve can be opened several times with a lifting wrench. Wash the dirt away. Damage to the sealing surface should be repaired by grinding or grinding after grinding according to the degree of damage. The stem is bent, tilted or the lever is deflected from the fulcrum to displace the spool and the disc and should be reassembled or replaced. If the spring elasticity is reduced or the elasticity is lost, measures such as replacing the spring and re-adjusting the opening pressure should be taken.
(2) does not turn on when the pressure is specified. The reason for this is:
The pressure is not allowed. The amount of compression of the spring or the position of the weight should be readjusted.
The valve flap is stuck to the seat. The safety valve should be manually drained periodically.
The lever of the lever safety valve is stuck or the weight is moved. The weight position should be re-adjusted and the lever movement should be automatic.
(c) Less than the prescribed pressure is turned on. The main reason is that the constant pressure is not accurate, the spring is aging, and the spring force is reduced. It should be adapted to tighten the valve stem or replace the spring.
(4) The pressure continues to rise after discharge. This is mainly because the selected safety valve displacement is less than the safety relief of the equipment, and the appropriate safety valve should be re-selected. The stem centerline is not right or the spring is rusting, so that the valve flap cannot be opened to the proper height. The valve stem should be reassembled or the spring replaced. If the exhaust pipe section is not enough, an exhaust pipe that meets the safe discharge area should be adopted.
5) The valve flaps or vibrates. Mainly because the spring stiffness is too large, the spring with appropriate stiffness should be used instead. If the adjustment ring is not properly adjusted and the seat pressure is too high, the adjustment ring position should be re-adjusted. The discharge pipe resistance is too large, causing excessive discharge back pressure.
(6) The valve flap does not return to the seat after discharge. This is mainly caused by the spring bending, the valve stem and the valve disc are not properly installed or stuck, and should be reassembled.
Fourth, maintenance and inspection of safety valves
For the safety valve to be sensitive, reliable and well sealed, maintenance and inspection must be enhanced during operation of the boiler, pressure vessel, and pressure piping.
(1) Always keep the safety valve clean and prevent the valve body spring from being filled or corroded by grease dirt, preventing the safety valve discharge pipe Blocked by oil or other foreign matter. Always check that the seal is intact and prevent the weight of the lever safety valve from loosening or being moved to prevent random rotation.
(2) When the safety valve is found to be leaking, it should be replaced and repaired. It is forbidden to eliminate the leakage by increasing the load (such as over-tightening the adjusting screw of the spring-type safety valve or adding weight to the lever of the lever safety valve). In order to prevent the valve disc and the valve seat from being stuck by dirt such as grease in the gas, the safety can not be opened normally, and it is safe for other gases used for air, steam or with sticky dirt but not harmful to the discharge. Valves should be tested on a portable discharge periodically.
(c) To keep the safety valve sensitive and reliable, perform at least one periodic calibration every year. Regularly verified content generally includes dynamic checks and disassembly checks. The main content of the dynamic inspection is to check the opening pressure of the safety valve, the return pressure, the degree of sealing and the opening height at the rated discharge pressure, etc., which are the same as those for the safety valve. If the dynamic inspection fails, or if an abnormality such as a leak is found during operation, it shall be disassembled. After disassembly, carefully check all parts of the safety valve for cracks, scratches, abrasion, corrosion, deformation, etc., and repair or replace according to the size and damage of the defect, and finally assemble for dynamic inspection.
Special equipment users should attach great importance to safety valve fault elimination, maintenance and inspection (maintenance) work, and related accident warnings and safety valves. The importance of pressure on special equipment. Special equipment production and use units, especially small and medium-sized private individual enterprises should study carefully, implement the "Special Equipment Safety Supervision Regulations", strictly abide by the safe operating procedures and rules and regulations, in addition to the pressure-bearing special equipment body in use In addition to regular routine maintenance and inspections, regular inspection and maintenance of its safety accessories shall be carried out according to regulations, and it shall be included in the safety management of special equipment, promptly rectify the hidden dangers discovered, eliminate hidden dangers, and truly implement the main body of the enterprise. Responsibility to ensure the safe operation of special equipment.
