valve operation


1. Correct operation of manual valve

Manual valve is a kind of valve commonly used in equipment and devices, which is operated by handle and handwheel. Under normal circumstances, the clockwise rotation of the handle and handwheel is specified as the closing direction, and the counterclockwise rotation is specified as the opening direction.However, the opening and closing direction of some valves is opposite to the above, so you should pay attention to checking the opening and closing signs before operating.
Manual valve, the size of its handle and hand wheel is designed according to normal manpower. Therefore, it is stipulated in the use of the valve that the operator is not allowed to open and close the valve with the help of a lever and a long wrench. At the same time, if the length of the handle and the diameter of the handwheel are less than 320mm, only one person is allowed to operate it; if the diameter of the handwheel is equal to or more than 320mm, two people are allowed to operate together, or one person is allowed to operate with an appropriate lever (generally the length does not exceed 0.5m). .However, diaphragm valves and non-metallic valves are strictly prohibited from using levers or long wrenches to operate, and it is also not allowed to use excessive or excessive force to close the valve.
Some operators are accustomed to using levers and long wrenches to operate manual valves, thinking that the greater the closing force, the better, but this is not the case. This can lead to premature valve damage and even an accident. Practice has proved that, except for the impact handwheel, operating the valve too large or too violently will easily damage the handwheel, handle, scratch the valve stem and sealing surface, and even crush the sealing surface. Secondly, when the handwheel and handle are damaged or lost, they should be assembled in time, and it is not allowed to use a live wrench instead.
Valves such as gate valves and globe valves should be rotated 1/4 to 1/2 turn when they are closed or opened to the end (ie, bottom dead center or top dead center) to make the thread fit better, so as to facilitate inspection during operation, so as not to screw Overtightening will damage the valve.
Larger diameter butterfly valves, gate valves and globe valves, and some are equipped with bypass valves. The function of the bypass valve is to balance the pressure difference between the inlet and outlet and reduce the opening torque. When opening, the bypass valve should be opened first, and then the large valve should be opened.
Before opening the steam valve, the pipeline must be preheated to drain the condensed water. Open slowly to avoid water hammer and damage to valves and equipment.
When opening and closing ball valves, butterfly valves and plug valves, when the groove on the top surface of the valve stem is parallel to the channel, it indicates that the valve is in the fully open position; when the valve stem is rotated 90 degrees to the left or right. When the groove is perpendicular to the channel, 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 vertically. The operation of the three-way and four-way valves should be carried out according to the marks of opening, closing and reversing, and the movable handle should be removed after the operation.
For gate valves and throttle valves with scales, check and adjust the fully open or fully closed indicating position. The rising stem gate valve and globe valve should also remember their fully open and fully closed positions, so as to avoid hitting the dead point when fully open. When the valve is fully closed, it can be found with the help of the ruler and mark that the closing piece falls off or resists foreign objects, so as to troubleshoot.
The newly installed pipes and equipment have a lot of dirt and welding slag on the inside. The normally open manual valve sealing surface is easy to stick to dirt, should use the slightly open method to let the high-speed medium wash away these foreign objects, and then gently close.
After some manual valves are closed, the temperature drops and the valve parts shrink, causing small gaps on the sealing surface and leakage. This should be closed again at an appropriate time after closing.
Whether the valve is operated correctly or not directly affects the service life of the valve.

2. Precautions for operating the valve

The process of operating the valve is also the process of inspecting and handling the valve. However, the following matters should be paid attention to when operating the valve.
①High temperature valve. When the temperature rises above 200°C, the bolts are heated and elongated, which is easy to make the valve seal loose. At this time, the bolts need to be “hot-tightened”, and it is not appropriate to perform the hot-tightening in the fully closed position of the valve, so as to avoid the valve stem from being dead and difficult to open later.
②In the season when the temperature is below 0°C, for valves that stop steam and water, pay attention to opening the valve seat plug to remove condensed water and accumulated water, so as to avoid freezing and cracking the valve. Pay attention to heat preservation for valves that cannot eliminate water accumulation and valves that work intermittently.
③ The packing gland should not be pressed too tightly, and the flexible operation of the valve stem should prevail (it is wrong to think that the tighter the packing gland is, the better, it will accelerate the wear of the valve stem and increase the operating torque). Under the condition of no protective measures, the packing can not be replaced or added under pressure.
④During the operation, the abnormal phenomena found by listening, smelling, seeing, touching, etc. should be carefully analyzed for the reasons, and the ones that belong to their own solutions should be eliminated in time;
⑤ The operator should have a special log or record book, and pay attention to record the operation of various valves, especially some important valves, high temperature and high pressure valves and special valves, including their transmission devices. They should be noted the failure, treatment, replacement parts, etc., these materials are important to the operators themselves, repairers and manufacturers. Establish a special log with clear responsibilities, which is beneficial to strengthen management.

3. Valve storage and maintenance

The purpose of storage and maintenance is to prevent the valve from being damaged or degraded during storage. In fact, improper storage is one of the important reasons for valve damage.
Valves should be kept in an orderly manner. Small valves should be placed on shelves, and large valves can be arranged neatly on the floor of the warehouse. They should not be piled up randomly, and the flange connection surface should not touch the ground. This is not only for aesthetics, but mainly to protect the valve from being damaged.
Due to improper storage and handling, the handwheel is broken, the valve stem is crooked, the fixing nut between the handwheel and the valve stem is loose and lost, etc. These unnecessary losses should be avoided.
For valves that will not be used in a short period of time, the asbestos packing should be removed to avoid electrochemical corrosion and damage to the valve stem.
The valves that have just entered the warehouse should be inspected. If rainwater or dirt has entered during transportation, they should be wiped clean and then stored.
The valve inlet and outlet should be sealed with wax paper or plastic sheets to prevent dirt from entering.
Anti-rust oil should be applied to the processing surface of the valve that can rust in the atmosphere to protect it.
The valve placed outdoors must be covered with rain-proof and dust-proof items such as linoleum or sheet cloth. The warehouse where the valve is stored should be kept clean and dry.

4. Valve use and maintenance

The purpose of use and maintenance is to prolong the life of the valve and ensure reliable opening and closing.
The stem thread is often rubbed with the stem nut, and a little yellow dry oil, molybdenum disulfide or graphite powder should be applied to lubricate.
For valves that are not frequently opened and closed, turn the handwheel regularly and add lubricant to the valve stem thread to prevent it from being bitten.
For outdoor valves, a protective cover should be added to the valve stem to prevent rain, snow, dust and rust.
If the valve is mechanically ready to move, add lubricating oil to the gearbox on time.
Always keep the valve clean.
Always check and maintain valve integrity. If the fixing nut of the handwheel falls off, it must be matched and cannot be used properly, otherwise it will grind the square on the upper part of the valve stem, and gradually lose the reliability of cooperation, and even cannot be started.
Do not rely on the valve to support other heavy objects, and do not stand on the valve.
The valve stem, especially the threaded part, should be wiped frequently, and the lubricant that has been soiled by dust should be replaced with a new one, because the dust contains hard debris, which is easy to wear the thread and the surface of the valve stem, affecting the service life.

5. Maintenance of valve packing

The packing is directly related to the key seal of whether leakage occurs when the valve is switched on and off. If the packing fails and causes leakage, the valve is equivalent to failure, especially the valve of the urea pipeline, because of its high temperature and corrosion, the packing is easy to age.Enhanced maintenance can extend the life of the packing
When the valve leaves the factory, in order to ensure the elasticity of the packing, it is generally subject to the static pressure test and no leakage. After the valve is installed in the pipeline, due to factors such as temperature, extravasation may occur. At this time, the nuts on both sides of the packing gland should be tightened in time, as long as there is no leakage, and if there is extravasation in the future, tighten it again, not once. Tightly die to avoid packing loss of elasticity and loss of sealing performance.
Some valve packings are equipped with molybdenum disulfide grease. After several months of use, the corresponding lubricating grease should be added in time. When it is found that the packing needs to be supplemented, the corresponding packing should be added in time to ensure its sealing performance.

6. Maintenance of valve transmission parts

During the valve opening and closing process, the originally added lubricating grease will continue to be lost, and the effect of temperature, corrosion and other factors will also make the lubricating oil continue to dry up. Therefore, the transmission parts of the valve should be checked frequently, and the oil shortage should be replenished in time to prevent the increase of wear due to the lack of lubricant, resulting in inflexible transmission or failure of the case.

7. Maintenance during valve grease injection

When injecting grease into the valve, the amount of grease is often ignored. After the grease injection gun is refueled, the operator selects the valve and the grease injection connection method, and then performs the grease injection operation. There are two situations: on the one hand, the amount of grease injection is small and the amount of grease injection is insufficient, and the sealing surface wears quickly due to the lack of lubricant. On the other hand, excessive fat injection results in waste. The reason is that there is no precise calculation of the sealing capacity of different valves according to the valve type category. The sealing capacity can be calculated according to the valve size and type, and then a reasonable amount of grease can be injected.
Pressure issues are often overlooked when valves are greased. During the grease injection operation, the grease injection pressure changes regularly with peaks and valleys. The pressure is too low, the seal leaks or fails, the pressure is too high, the grease injection port is blocked, the sealing inner grease is hardened, or the sealing ring is locked with the valve ball and valve plate. Usually, when the grease injection pressure is too low, the injected grease mostly flows into the bottom of the valve cavity, which usually occurs in small gate valves. If the grease injection pressure is too high, on the one hand, check the grease injection nozzle, and replace it if the grease hole is blocked. . In addition, the sealing type and sealing material also affect the grease injection pressure. Different sealing forms have different grease injection pressures. Generally, the grease injection pressure of hard seals is higher than that of soft seals.
When injecting grease into the valve, pay attention to the problem that the valve is in the switch position. The ball valve is generally in the open position during maintenance, and in special cases, it is selected to be closed for maintenance. Other valves can not be regarded as open position. The gate valve must be closed during maintenance to ensure that the grease fills the sealing groove along the sealing ring. If it is opened, the sealing grease will fall directly into the flow channel or valve cavity, causing waste.
When the valve is greased, the effect of grease injection is often ignored. During the grease injection operation, the pressure, grease injection volume, and switch position are all normal. However, in order to ensure the grease injection effect of the valve, it is sometimes necessary to open or close the valve, check the lubrication effect, and confirm that the surface of the valve ball or gate plate is evenly lubricated.
When injecting grease, pay attention to the valve body blowdown and wire plug pressure relief problems. After the valve pressing test, the gas and water in the valve cavity of the sealing cavity will increase due to the increase of the ambient temperature. When injecting grease, it is necessary to discharge the sewage and release the pressure first, so as to facilitate the smooth progress of the grease injection. The air and moisture in the sealed cavity are fully replaced after grease injection. The valve cavity pressure is released in time, which also ensures the safety of the valve. After the grease injection, be sure to tighten the drain and pressure relief plugs to prevent accidents.
When injecting grease, pay attention to the problem of uniform grease. During normal grease injection, the grease discharge hole closer to the grease injection port first discharges fat, then reaches the low point, and finally the high point, and then discharges fat one by one. If it does not follow the rules or there is no fat, it proves that there is a blockage, and it should be cleaned in time.
When injecting grease, also observe that the valve diameter is flush with the sealing ring seat. For example, for a ball valve, if there is interference in the opening position, adjust the opening position limiter inward to confirm that the diameter is straight and then lock. Adjusting the limit should not only pursue the opening or closing position, but consider the whole. If the opening position is flush and the closing position is not in place, the valve will not close tightly. In the same way, if the adjustment of the closed position is in place, the corresponding adjustment of the open position should also be considered. Make sure the valve has a right angle of travel.
After grease injection, be sure to seal the grease injection port. To avoid the entry of impurities or the oxidation of lipids at the grease injection port, the cover should be coated with anti-rust grease to avoid rusting. for the next operation.
When injecting grease, consideration should also be given to the specific treatment of specific problems in the sequential transportation of oil products in the future. Given the different qualities of diesel and gasoline, the scour and disintegration ability of gasoline should be considered. In the future valve operation, when encountering gasoline section operations, the grease should be replenished in time to prevent the occurrence of wear.
When injecting grease, do not neglect the grease injection at the valve stem. There are sliding bushings or packings on the valve shaft, which also needs to be kept lubricated to reduce the frictional resistance during operation. If lubrication cannot be ensured, the torque will increase the wear parts during electric operation, and the switch will be laborious during manual operation.
Some ball valves are marked with arrows. If there is no English FIOW handwriting, it is the direction of action of the sealing seat, not as a reference for the flow direction of the medium, and the direction of the valve self-leakage is opposite. Typically, double seated ball valves have bidirectional flow.
When maintaining the valve, also pay attention to the problem of water inflow in the electric head and its transmission mechanism. Especially the rain that seeps in during the rainy season. One is to rust the transmission mechanism or the transmission sleeve, and the other is to freeze in winter. When the electric valve is operated, the torque is too large, and the damage to the transmission parts will make the motor no-load or over-torque protection trip, and the electric operation cannot be realized. The transmission parts are damaged, and manual operation cannot be carried out. After the over-torque protection action, manual operation is also unable to switch, such as forced operation, it will damage the internal alloy parts.
Valve maintenance must be treated with a scientific attitude, so that the valve maintenance work can achieve its due effect and application purpose. In order to make production run normally, reduce parking and increase economic benefits, in terms of valves, these three points must be done well:
1. The correct selection of valves is the basis.
2. Correct use of the valve is critical.
3. Correct maintenance is the guarantee.

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