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Operation and Use of Valve After the valve is installed, the operator can be familiar with the structure and performance of the valve and transmission device, correctly identify the valve's opening direction, opening mark, indication signal, etc., and can operate the valve skillfully and accurately, and handle various emergency faults in a timely and decisive manner. Whether the valve is operated correctly or not directly affects its service life, and is related to the stable and safe production of equipment and devices. XV Operation of manual valves Manual valves operate the valves through handwheels and handles. They are widely used in petrochemical plants. Operators should pay attention to the following points: ◆The opening direction of the valve, usually counterclockwise means the valve is open, and clockwise means the valve is closed. Therefore, when switching the valve, pay attention to the direction ◆The handle of the valve, the hand * * The small one is designed based on the manual switch of the valve. Therefore, the valve can be opened and closed by manually turning the valve. It is generally not allowed to use a lever or wrench to open and close the valve. In order to prevent excessive force from damaging the sealing surface and other parts. ◆ When opening the closed gate valve and stop valve to the dead center, turn 1/4 to 1/2 turn to make the threads more tightly sealed to avoid over-tightening and damage to the valve parts. ◆ Do not use the gate valve and stop valve for throttling. This will easily wash away the valve plate and sealing surface, and introduce vibration leakage and damage the valve. ◆ When opening the steam valve, it should be opened slowly to remove the condensed water in the pipe and prevent water hammer. Damage to valves and pipelines ◆ Large-diameter gate valves, globe valves and butterfly valves, some are equipped with bypass valves, whose function is to balance the pressure on both sides of the valve and reduce the opening force. Therefore, when opening, you should open the bypass valve first, and then slowly open the valve. When closing the valve, you should close the bypass valve first, and then slowly close the main valve. ◆ After some valves are closed, after the temperature drops, the valve parts shrink, and slight leakage occurs on the sealing surface. At this time, you should wait until the valve is closed, and then tighten the valve appropriately to operate the valve automatically. ◆ Before the trap is activated, the dirt and impurities in the pipeline should be discharged to prevent it from being blocked by debris and unable to work normally. 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 it only discharges water, it means that the valve is working normally. ◆Safety valve Safety valves should be regularly inspected for constant pressure, and constant pressure records and labels should be made. Before installation, they 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 safety valve online adjustment instruments, which are composed of mechanical, hydraulic and electronic records. The advantages are that the working conditions are more in line with actual production, the data is more real, and it does not affect production, does not require disassembly and transportation, and can improve the adjustment rate of safety valves. The disadvantage is that it can only be used for spring safety valves, and there must be threads on the valve stem. ； Must know the average diameter of the valve sealing surface ； It is impossible to clean, grind, replace parts and perform air tightness tests on the safety valve. 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 discharge dirt, etc. ◆ Before the pressure reducing valve is activated, open the bypass valve or flushing valve to clean the pipeline. 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 operating procedures, and be able to operate independently. Precautions during valve operation ◆ Prevent valves from being staggered, wrongly closed, missed opening, or missing closing. 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 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 working 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, valve body leakage, and sealing surface or lining material leakage according to its external structure. Operators should make accurate judgments. If they can solve it 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 will cause media leakage and cause danger.