Thread Content
I. What are the issues to be mindful of when using valves? 1. When using an electric gate valve, pay attention to whether the handwheel is disengaged and whether the lever is in the electric position. If proper disengagement is not ensured, should the protective device fail during motor startup, the handle may rotate at high speed and injure the operator. 2. When manually opening or closing the gate valve, it should be noted that the force applied generally should not exceed 15 kg. If it feels very difficult to operate the valve, it indicates that there may be issues such as rusted or stuck valve stem, or a bent valve stem; in such cases, using more force could damage the valve stem, so the valve should be operated only after the problem has been resolved ； After the gate valve is closed, the valve handle should be turned counterclockwise by one-sixth turn, which helps to restart the gate. 3. The torque limiting mechanism of the electric gate valve not only serves to provide torque protection, but also acts as a backup stop protection in case the stroke control mechanism fails during operation. Its operating torque is adjustable, and it should be adjusted at any time to remain within the torque range specified in the manual. A few gate valves use torque-limiting mechanisms to control the gate or the pressure on it; examples include certain flap-type gates and conical sludge valves. If the adjusting torque is too low, the valve cannot close properly ； Conversely, this will damage the connecting rod; therefore, extra care must be taken in adjusting the torque. 4. The pointer of the valve opening indicator should be adjusted to the correct position. To do this, first close the valve, set the pointer to zero, and then gradually open it ； When the valve is fully open, the pointer should point exactly to the fully open position. Correct instructions help the operator understand the situation and also facilitate the detection of faults; for example, if the motor stops rotating while the pointer is not at the fully open position, it can be inferred that the valve may be stuck. 5. Long-term closed sewage valves sometimes create a dead zone near them, where sediment can accumulate; this sediment poses resistance to the opening and closing of the butterfly valve. If increased resistance is encountered when opening the valve, do not force it open; instead, repeat the opening and closing actions to help the water carry away the deposits, and then open the valve once the resistance decreases. At the same time, if it is observed that sand tends to accumulate around the valve, it should be opened for a few minutes from time to time to help remove the accumulated sand. Similarly, valves that are not operated for extended periods should also be turned on and off once or twice regularly to prevent rusting or blockage. 6. When opening or closing valves on dark-pipe sewage or sludge pipes that have not been used for a long time, attention should be paid to ventilation at the operation site. In the valve chamber above a valve that has not been moved for a long time, toxic and harmful gases such as sewage, sludge, and hydrogen sulfide produced by anaerobic decomposition may accumulate; when the valve is turned, gases like hydrogen sulfide may escape from the packing around the valve stem. In particular, hydrogen sulfide gas is a highly toxic nerve agent that can easily cause injuries to people. At this time, ventilation at the site, especially in the valve chambers, is extremely necessary. II. What are the causes of common valve failures and their solutions? 1. The closing components such as the gate plates are damaged. The reason is improper material selection or the frequent use of valves on pipelines as control valves, with high-speed flowing media causing wear on the sealing surfaces. At this point, the cause of the damage should be identified, and closing elements made of other materials should be used. When there are many impurities in the high-pressure water being transported, avoid using the closed-loop valve as a regulating valve. 2. Leakage in the sealed chamber. The main reasons are incorrect selection or packing method of the packing, as well as quality issues with the valve stem. First, the appropriate packing should be selected, and it should be installed in the seal chamber in the correct manner. When the conveying medium exceeds 100°C, oil-impregnated packing is not used; instead, heat-resistant graphite packing is employed. 3. Poor sealing. The installation procedures were not followed before installing the valve; for example, the dirt inside the valve chamber was not cleaned, and weld slag, rust, sediment, or other mechanical impurities remained on its surface. This led to defects such as scratches and dents on the sealing surface, causing valve failures. Therefore, it is necessary to strictly follow the installation procedures to ensure the quality of installation. Due to insufficient manufacturing precision, the valve itself may result in a poor fit between the seal and the closing element, and in such cases it must be repaired or replaced. Applying too much force when closing the valve can also cause damage to the sealing components; appropriate force must be used during operation. 4. It cannot be closed once opened. This situation often occurs with gate valves. The structure of such valves is such that the gate is divided into two parts which are clamped around the stem head, and the stem is used to move the gate open and closed. In some valves, the two valve plates are not fixed to each other; if the valve is opened too far, the two plates may separate, causing the valve stem to come out and preventing the valve from being closed. In such cases, the valve must be disassembled and its components realigned. 5. The spring of the safety valve and pressure relief valve is damaged. The cause of spring damage is often an inappropriate choice of spring material or issues with the quality of spring manufacturing; it is necessary to replace the spring material or use springs of higher quality. 6. The valve stem does not move smoothly up and down. The surface roughness of the thread does not meet the requirements; it needs to be ground again. The valve stem and valve stem liner are made of an inappropriate material or the material choice is incorrect. When the valve stem is made of carbon steel or stainless steel, bronze or chromium-containing cast iron should be used as the material for the valve stem bushing. If wear is detected on the valve stem threads, a new valve stem bushing or a new valve stem should be replaced. When transporting high-temperature media, lubrication should not cause rust; therefore, pure graphite should be used as a lubricant for such transportation. If slight rust on the valve stem causes it to move inflexibly, a hammer can be used to gently tap the valve stem bushing, turning the stem free before applying lubricant. III. How to operate valves driven by electric devices correctly? When the electric device is started, the start button on the electrical panel should be pressed; the motor will then begin to operate. After a certain period of time, the motor stops running automatically, and the \"Running\" indicator light on the electrical panel should turn on ； If the valve is to be closed, press the close button on the electrical panel; the valve will move in the closing direction, and after a certain period of time it will be fully closed, at which point the \"Closed\" indicator light will turn on. During valve operation, the signal light indicates the intermediate state of being open or closed. If the valve’s indication signal matches its actual operation, and it can close tightly and open fully, this indicates that the electric actuator is functioning properly. If the signal light does not illuminate while the unit is in operation, and when the valve is fully open or fully closed, but the emergency signal light turns on, it indicates that the drive mechanism is malfunctioning. It is necessary to check the cause, carry out repairs, and re-debugging can be done by referring to the operating instructions for the valve actuator. In most cases, the solution is to adjust the limit switch to the correct position. When an electric actuator needs to be addressed promptly due to a fault or improper shutdown, the control lever should be moved to the manual position; turning the handwheel clockwise closes the valve, while turning it counterclockwise opens it. The electric device cannot be operated in reverse mode while it is running. When an incorrect operation needs to be corrected, press the stop button and then restart it. IV. What precautions should be taken when operating valves? For high-temperature valves, when the temperature rises above 200°C, the bolts expand due to heat, which can lead to poor sealing of the valve. In such cases, it is necessary to \"heat-tighten\" the bolts. This process should not be carried out with the valve in its fully closed position, as this may cause the valve stem to get stuck and make it difficult to open the valve later on. During seasons when the temperature is below 0°C, for valves that supply gas or water, it is necessary to remove the plug at the bottom of the valve in order to drain out condensed water and accumulated water, preventing the valves from cracking due to freezing. Attention should be paid to insulation for valves that cannot drain water and those that operate intermittently. The packing gland should not be tightened too much; flexibility in valve stem operation should be the guiding principle. The idea that the gland should be tightened as much as possible is incorrect, as it accelerates the wear of the valve stem and increases the operating torque. Without protective measures, do not replace or add packing under pressure casually. When abnormal phenomena are detected through listening, smelling, observing, and touching during operation, the operator must carefully analyze their causes. If the issue can be resolved by the operator themselves, it should be fixed promptly; if it requires the help of a repair technician, the operator should not try to fix it on their own to avoid delaying the repair process. Operators should keep a dedicated log or record book to carefully document the operation status of various valves, especially those that are important, high-temperature and high-pressure valves, as well as special valves. This includes information on the valve’s actuation mechanisms, any failures that occur along with their causes, the methods used to address them, and the parts that were replaced. Such information is undoubtedly very valuable for the operators themselves, maintenance personnel, and the manufacturers. Establishing dedicated logs with clear responsibilities helps to improve management. V. How to maintain and service valves during normal operation? The purpose of maintenance during valve operation is to ensure that the valve remains clean, properly lubricated, has all its components in place, and functions normally throughout the year. Cleaning of the valve. The surface of the valve, the trapezoidal threads on the valve stem and valve stem nut, the sliding parts between the valve stem nut and the bracket, as well as components such as gears, turbines, and worm gears, are prone to accumulating dirt such as dust, oil residues, and medium residues, which can cause wear and corrosion to the valve. Therefore, it is clearly very important to keep the outside of the valve and its moving parts clean in order to preserve the integrity of the valve’s paint. Dust on valves can be removed by brushing or blowing with compressed air; dirt between trapezoidal threads and teeth can be wiped off using a cloth ； Oil stains and residue from the medium on the valves can be removed by steam cleaning; even a wire brush can be used for cleaning, until the machined surfaces and mating surfaces exhibit a metallic luster, and the painted surfaces show their original color. A dedicated person should be responsible for the steam trap, checking it at least once per shift. The plug at the bottom of the steam trap should be opened regularly to flush it, or the trap itself should be taken apart for cleaning on a regular basis, in order to prevent dirt from blocking the valve. Good lubrication is required for the trapezoidal threads of valves, the valve stem nuts and the sliding parts of the supports, the bearing areas, gears and turbines, the meshing parts of worm gears, as well as other moving parts that are in contact with each other, in order to reduce friction between them and prevent wear. Some parts are equipped with dedicated oil cups or oil nozzles; if these become damaged or lost during operation, they should be repaired and replaced, and the oil pathways must be kept unobstructed. Lubrication of valves. The lubricated parts should be refueled regularly according to specific conditions. Valves that are often opened and have high oil temperatures are suitable for being refueled once every week to month ； For valves that are not frequently opened and operate at low temperatures, the lubrication interval can be longer. Lubricants include machine oil, butter, molybdenum disulfide, graphite, etc. High-temperature valves are not suitable for oil or butter, as they will melt due to the high temperatures and thus be lost; instead, molybdenum disulfide and graphite powder are appropriate for use in these valves. For exposed parts that require lubrication, such as trapezoidal threads and gears, using greases like butter makes it easy for dust to accumulate, whereas lubrication with molybdenum disulfide and graphite powder reduces the risk of dust accumulation and provides a better lubricating effect than butter. Graphite powder is not easy to apply directly; it can be mixed with a small amount of machine oil or water to form a paste for use. Additionally, the exposed screws should be cleaned thoroughly and coated with new lubricant at least once a year. Gland-sealed plug valves should be lubricated at regular intervals; otherwise, they are prone to wear and leakage. For some internally screw-type valves, whose screws are in constant contact with sewage, the accumulated dirt should be cleaned regularly, after which a lubricant resistant to water erosion should be applied. VI. What are the operating methods for manual valves? Manual valves are valves that are operated using handles or handwheels; they are a commonly used type of valve in equipment pipelines. For its handle and handwheel, clockwise rotation closes it, while counterclockwise rotation opens it. However, there are also individual valves that open in the opposite direction to the aforementioned opening direction. Therefore, it is necessary to check the activation flag before proceeding with the operation. The handles and handwheels on the valves are designed for normal human strength; therefore, it is specified that operators are not allowed to use levers or long wrenches to open or close the valves. For handwheels and handles with a diameter of less than 320 mm, operation by a single person is permitted only; for handwheels with a diameter greater than 320 mm, operation by two people together is allowed, or one person can operate the valve with the help of an appropriate lever (usually not longer than 0.5 m). However, diaphragm valves, clamp valves, and non-metallic valves must not be operated using levers or long wrenches, nor should the valves be closed too abruptly. Valves such as gate valves and globe valves need to be rotated 1/4–1/2 turn to reach the fully closed or fully open position (i.e., the bottom or top dead center), in order to achieve a better seal between the threads and to facilitate operation, thereby preventing the valves from being tightened too much and damaged. Some operators* are accustomed to using levers and long wrenches, believing that the greater the closing force, the better – but this is not the case. This can cause the valve to fail prematurely, and even lead to accidents. Apart from impact-type handwheels, experience has shown that operating valves in an excessive or forceful manner can easily damage the handle and handwheel, abrade the valve stem and sealing surfaces, and even crush the sealing surfaces. When a handwheel or handle is damaged or lost, it is generally not allowed to use an adjustable wrench as a substitute; one should obtain a replacement promptly. Larger-diameter butterfly valves, gate valves, and globe valves are sometimes equipped with bypass valves, whose function is to balance the pressure difference between the inlet and outlet and reduce the force required to open them. When starting up, the bypass valve should be opened first; once the pressure difference across the valve has decreased, then the main valve can be opened. When opening the valve, first close the bypass valve, and then close the main valve. When opening the valve for the steam medium, it is necessary to preheat the pipeline first and remove any condensate water. The opening process should be carried out slowly to avoid water hammer effects that could damage the valve and equipment. When opening ball valves, butterfly valves, and plug valves, if the groove on the top surface of the valve stem is parallel to the passage, it indicates that the valve is in the fully open position ； When the valve stem rotates 90° to the left or right, the groove is perpendicular to the channel, indicating that the valve is in the fully closed position. Some ball valves, butterfly valves, and plug valves are opened with the wrench parallel to the channel and closed with it vertical. The operation of three-way and four-way valves should be carried out according to the open, close, and reverse markings. After the operation is complete, the movable handle should be removed. For gate valves and stop valves equipped with scales, the indication positions for full open or full closed states should be checked and adjusted properly. For straight-through gate valves and globe valves, it is also important to remember their fully open or fully closed positions, so as to avoid hitting the dead center when they are fully open. When the valve is fully closed, a scale and markings can be used to detect whether the closing element has fallen off or is being held back by foreign objects, thereby preventing malfunctions. When operating valves, gate valves, globe valves, and similar types should not be used as shut-off valves, as this can easily cause erosion of the sealing surfaces and lead to premature damage of the valves. Newly installed pipes, equipment, and valves often have a lot of dirt on their inner surfaces, as well as welding slag and other debris. The sealing surfaces of valves that are kept open can also accumulate dirt; it is therefore necessary to open the valves slightly so that the high-speed flow of fluid can wash away these contaminants, after which the valves should be closed gently. Repeating this process of opening and closing slightly several times will help to clean them thoroughly. After some valves are closed, the temperature drops and the valve components contract, causing small gaps to appear in the sealing surfaces and leading to leaks. After it is closed in this way, turn the valve on and off again at an appropriate time.