Drain valve: Before being used, the dirt and impurities in the pipeline should be discharged to prevent it from being blocked by debris and failing to work properly. During operation, check the working condition of the trap. If too much steam is discharged, it means that the valve is not working properly. If only water is discharged, it means that the valve is working normally.
​Safety valve: The safety valve should undergo constant pressure inspection regularly, and the constant pressure records and labels should be made. Before installation, it should pass the pressure test and constant pressure inspection. In the past, safety valves used offline adjustment, and production units had a set of scientific management methods. In recent years, some units have introduced online safety valve adjustment instruments, which are composed of mechanical, hydraulic and electronic records. Its advantages are that the working conditions are more in line with actual production, the data is more real, and it does not affect production and does not require disassembly and assembly. and transportation, and can improve the adjustment rate of the safety valve. The disadvantages are that it can only be used for spring safety valves, and there must be threads on the valve stem; the average diameter of the valve sealing surface must be known; the safety valve cannot be cleaned, ground, replaced, and airtight tested. If the safety valve cannot return to its seat after tripping, a large amount of material will be released and production will be affected. Measures should be taken immediately to deal with it. The method is to use a hand plate to lift the safety valve with a wrench, and open it once in a while to drain dirt, etc.
Pressure reducing valve: Open the bypass valve or flushing valve to clean the pipeline before activation. After the pipeline is clean, close the bypass valve and then activate the pressure reducing valve.
Operation of other valves
Other valves use electric, electromagnetic, pneumatic and hydraulic devices to open and close valves. Remote control is achieved by instruments, electric switches, etc. Therefore, operators should have a detailed understanding of the relevant structural characteristics and working principles of separately operated valves, be familiar with the operating procedures, and be able to operate independently, rather than performing emergency treatment in an accident state.
Things to note when operating the valve:
Prevent valves from being mis-opened, mis-closed, missed-opened, and missed-closed. Operators must clearly understand the function of each valve and its position in the process pipeline to prevent misoperation, otherwise it may cause accidents such as material leakage, mixing, and pressure suppression. For example, in an oil refining unit, a steam purge was performed before starting the operation, and a vent valve leaked after being purged. As a result, when the operation was started, 370°C high-temperature oil slurry was discharged from the vent valve, causing a fire and shutting down the import unit.
In seasons when the low temperature is below 0℃, it is necessary to prevent freezing of deactivated valves, and promptly open the valve bottom plug to drain the condensed water inside. Warming measures should be taken for valves that cannot be eliminated and those that work intermittently.
For valves operating at high temperatures, when the temperature rises above 200°C, the bolts will elongate due to heat, which may easily cause the valve to become loosely sealed. The bolts should be “heat-tightened” when necessary. When hot-tightening, it should not be done in the fully closed position of the valve. This will prevent the valve stem from being stuck and making it difficult to open again.
When a valve leaks, the location and cause of the leak should be identified first. Generally, it is divided into two types: internal leakage and external leakage. External leakage is divided into packing leakage, valve cover leakage, valve body leakage, and sealing surface or lining material leakage according to its external structure. Operators should make accurate judgments about leaks. If they can solve the problem themselves, they should deal with it in time. If they cannot solve it, maintenance workers should deal with it in time.
The valve packing gland should not be pressed too tightly, so that the valve stem can rotate flexibly. Pressing it too tight will increase the friction of the valve stem, increase the operating torque, etc. When the valve is working, it is generally not allowed to replace or add packing under pressure. Otherwise, it may cause media leakage and cause danger.