Experience in valve operation

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After the valve is installed, operators can become familiar with its structure and performance as well as those of the driving mechanism. They are able to correctly identify the valve’s opening direction, opening degree indicators, and signaling devices, and can operate the valve skillfully and accurately, handling various emergency faults in a timely and decisive manner. Whether the valve is operated correctly has a direct impact on its service life, as well as on the smooth and safe operation of the equipment and systems. Operation of manual valves. Manual valves are operated using handwheels or handles, and they are widely used. Operators should pay attention to the following points: ◆ The direction in which the valve opens – generally, turning counter-clockwise opens the valve, while turning clockwise closes it. ◆The handle of the valve is designed for manual operation of the valve. Therefore, the valve can be opened and closed simply by turning it manually; it is generally not allowed to use levers or wrenches to operate the valve. To prevent excessive force from damaging the sealing surfaces and other components. ◆ Gate valves and stop valves should not be used for throttling, as this can easily erode the valve discs and sealing surfaces, cause vibrations and leaks, and damage the valves. ◆When opening the steam valve, it should be done slowly to remove the condensed water from the pipes, thereby preventing water hammer effects that could damage the valve and the pipes. ◆Large-diameter gate valves, globe valves, and butterfly valves are sometimes equipped with bypass valves, which serve to balance the pressure on both sides of the valve and reduce the force required to open it. Therefore, when opening it, the bypass valve should be opened first, followed by the gradual opening of the main valve; when closing it, the bypass valve should be closed first, followed by the gradual closing of the main valve. ◆After certain valves are closed, as the temperature drops, the valve components contract and minor leaks occur at the sealing surfaces; in such cases, it is sufficient to tighten the valve again after it has been closed. Operation of automatic valves: Before activation, the dirt and impurities in the pipes should be removed to prevent blockages that could prevent proper operation. During operation, check the performance of the steam trap; if too much steam is discharged, it indicates that the valve is not functioning properly, while if only water is discharged, it means the valve is working correctly. ◆Safety valves: Safety valves should be regularly tested at a specified pressure, and records and markings of this pressure testing should be kept. Before installation, they must pass pressure testing and the specified-pressure inspection. In the past, safety valves were adjusted offline, and production units had a set of scientific management methods. In recent years, some organizations have introduced online safety valve calibrators, which consist of mechanical, hydraulic, and electronic recording components. Their advantages include operating conditions that better reflect actual production realities, more accurate data, the ability to function without disrupting production, no need for disassembly or transportation, and an increased rate of safety valve calibration. The downside is that it can only be used with spring safety valves, and the valve stem must have threads ； It is necessary to know the average diameter of the valve sealing surface ； It is not possible to clean, grind, replace parts, or perform a leak test on the safety valve. If the safety valve fails to return to its original position after activating, it will cause significant material leakage, affecting production; immediate action must be taken to address this issue. The method is to lift the safety valve with a wrench by hand, and open it from time to time to discharge dirt and other debris. Other valves are operated to open and close using devices such as electric, electromagnetic, pneumatic, and hydraulic systems. Remote control is achieved through instruments, electric switches, etc. Therefore, operators should have a thorough understanding of the structural features and working principles of the valves they operate, be familiar with the operating procedures, and be able to carry out operations independently, which is beneficial for carrying out emergency responses in case of accidents. Precautions for valve operation: ◆ Prevent the valves from being opened or closed incorrectly, or from leaking. Operators must be fully aware of the function of each valve and its location in the process pipeline to avoid misoperations, as this could lead to accidents such as material leakage, mixing of materials, or pressure buildup. In the case of a certain refinery unit, steam purging was carried out before it was put into operation. One of the vent valves failed to close properly after being purged; as a result, during operation, hot oil slurry at 370°C flowed out through that vent valve, causing a major fire that led to the shutdown of the unit. ◆During seasons with low temperatures below 0°C, for valves that are not in use, it is essential to prevent freezing by promptly removing the plug at the bottom of the valve in order to drain any accumulated water inside. Insulation measures should be taken for valves that cannot be excluded from operation and those that operate intermittently. ◆For valves that operate at high temperatures, when the temperature rises above 200°C, the bolts expand due to heat, which can lead to poor sealing of the valve. It is necessary to \"heat-tighten\" the bolts when needed; however, this should not be done when the valve is in its fully closed position. To prevent the valve stem from getting stuck and making it difficult to open again. ◆When a valve leaks, it is necessary to first identify the location and cause of the leak. Generally, leaks can be categorized as internal or external. External leaks can be further divided, based on the valve’s external structure, into leaks at the packing area, leaks in the valve cover or body, and leaks in the sealing surfaces or lining materials. Operators should make an accurate assessment; any leaks that can be resolved on their own should be dealt with promptly, while those that cannot be fixed should be addressed by maintenance personnel as soon as possible. ◆The valve packing gland should not be tightened too much; it is sufficient for the valve stem to rotate freely. Tightening it excessively increases the friction on the valve stem and raises the operating torque. When the valve is in operation, it is generally not permissible to replace or add packing under pressure; otherwise, it may lead to medium leakage and pose a danger.