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Valve Operation And Maintenance
Apr 01, 2019

Valve operation and maintenance

1. Correct operation of manual valve

Manual valve is a kind of valve widely used in equipment and devices. It is operated by handles and handwheels. Generally, the clockwise rotation of the handle and handwheel is defined as the closing direction, and the counter-clockwise rotation is defined as the opening direction. However, some valves open and close in the opposite direction, so before operation, attention should be paid to check the opening and closing signs before operation.

The size of handle and handwheel of manual valve is designed according to normal manpower. Therefore, in the use of valves, it is stipulated that operators are not allowed to use lever and long wrench to open and close valves. At the same time, only one person is allowed to operate wheels with a handle length and a handwheel diameter less than 320 mm; wheels with a diameter equal to or greater than 320 mm allow two people to operate together or one person to operate with appropriate levers (usually no more than 0.5 mm in length). However, diaphragm valves and non-metallic valves are strictly prohibited from using lever or long wrench operation, nor are they allowed to close valves with excessive and violent force.

Some operators are accustomed to using lever and long wrench to operate manual valves. They think that the greater the closing force, the better. In fact, it is not. This will cause premature valve damage, or even accident. Practice has proved that besides impact handwheel, it is easy to damage handwheel and handle, scratch valve stem and sealing surface, or even press sealing surface if the valve is operated too large and too violently. Secondly, when the handwheel or handle is damaged or lost, it should be matched in time and not allowed to use the movable wrench instead.

Valves such as gate valves and globe valves should turn 1/4 to 1/2 turns when they are closed or opened to the end (i.e. lower or upper dead points), so that the threads are better tightened, so as to facilitate inspection during operation, so as not to tighten and damage the valve.

Large caliber butterfly valves, gate valves and globe valves, some with bypass valves. The function of bypass valve is to balance the pressure difference between inlet and outlet and reduce the opening moment. 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 discharge the condensate water. Open slowly to avoid water hammer and damage to valves and equipment.

When opening and closing ball valves, butterfly valves and cock valves, when the groove on the top of the stem is parallel to the passage, it indicates that the valve is in full open position; when the stem rotates 90 to the left or right. When the groove is perpendicular to the channel, it indicates that the valve is in full closed position. Some ball valves, butterfly valves and cock valves are opened parallel to the channel by wrench and closed vertically. The operation of three-way and four-way valves should be carried out according to the marks of opening, closing and reversing. After operation, the movable handle should be removed.

For gate valves and throttle valves with gauges, check and adjust the indication position of full opening or full closing. Open-rod gate valves and globe valves should also remember their full open and closed positions, so as to avoid the full open jamming dead point. When the valve is completely closed, the shutter can be found to fall off or hold foreign bodies with the help of a ruler and marking, so as to troubleshoot.

The newly installed pipelines and equipment have more internal dirt and welding ballast. It is easy to stick dirt on the sealing surface of manual valves which are normally opened. The micro-opening method should be adopted to let the high-speed medium wash away these foreign bodies and then close them gently.

After some manual valves are closed, the temperature drops and the valve parts shrink, resulting in small seams on the sealing surface and leakage. This should be done again at an appropriate time after the closure.

Whether the valve is operated correctly or not directly affects the service life of the valve.

 

2. Notes for Valve Operation

The process of operating the valve is also the process of checking and handling the valve. However, the following points should be noted when operating the valve.

High temperature valves. When the temperature rises above 200 C, the bolt is heated and elongated, which makes the valve easy to seal tightly. At this time, bolts need to be "hot tightened" and it is not appropriate to do it in the full closed position of the valve when hot tightening, in order to avoid the stem dead and difficult to open later.

(2) In the season when the temperature is below 0 C, attention should be paid to opening the valve seat wire plug to remove condensate and accumulated water so as not to freeze and crack the valve. For valves that cannot eliminate water accumulation and valves that work intermittently, attention should be paid to insulation.

(3) Packing gland should not be pressed too tightly, and should be based on the flexible operation of the valve stem. (It is wrong to think that the tighter the packing gland is pressed, the better it will speed up the wear of the valve stem and increase the operating torque.) In the absence of protective measures, it is not possible to replace or add fillers under pressure.

(4) In operation, the abnormal phenomena found by listening, hearing, looking and touching should be carefully analyzed, and the causes should be eliminated in time for their own solution; if the repairman is needed to solve them, he should not make do with it so as to avoid delaying the repair time.

(5) Operators should keep a special log or record book to record the operation of various types of valves, especially some important valves, high temperature and high pressure valves and special valves, including their transmission devices. It should be noted that the faults, handling methods, replacement parts and so on, which are important to the operators themselves, repairmen and manufacturers. Establishing a special log with clear responsibilities will help strengthen management.

 

3. Valve Maintenance

The purpose of storage and maintenance is not to let the valve be damaged in storage or to reduce the quality. In fact, improper storage is one of the important reasons for valve damage.

Valve storage, should be well organized, small valves on the shelf, large valves can be orderly arranged on the warehouse floor, not disorderly stacking, do not let the flange connection surface contact the ground. This is not only for the sake of beauty, but also to protect the valve from being damaged.

These unnecessary losses should be avoided due to improper storage and handling, broken handwheel, crooked stem, loosening and loss of fixed nuts between handwheel and stem, etc.

For valves that are not used for a short time, asbestos packing should be removed to avoid electrochemical corrosion and damage to the valve stem.

Valves that have just entered storage should be inspected. If rainwater or dirt is introduced during transportation, they should be cleaned and stored.

Valve inlet and outlet should be sealed with wax paper or plastic sheet to prevent dirty things from entering.

Protect the surface of valves that can rust in the atmosphere with anti-rust oil

Valves placed outdoors must be covered with rain and dust-proof materials such as linoleum or tarpaulin. Storage of valves should be kept clean and dry.

 

4. Use and maintenance of valves

The purpose of operation and maintenance is to prolong the life of valves and ensure the reliability of opening and closing.

Stem threads, often rubbed against stem nuts, should be coated with a little butter, molybdenum disulfide or graphite powder to lubricate them.

Valves that do not open and close frequently should also rotate the handwheel regularly and lubricate the stem threads to prevent biting.

Outdoor valves should be protected against rain, snow, dust and rust by adding a protective cover to the stem

If the valve system is mechanical, lubricating oil should be added to the gearbox on time.

Keep valves clean regularly

Always check and maintain the integrity of the other parts of the valve. If the fixed nut of the handwheel falls off, it should be well matched and not suitable for use. Otherwise, it will grind the four sides of the upper part of the valve stem, gradually losing the reliability of the matching, or even unable to start.

Do not rely on valves to support other weights, do not stand on valves

Stem, especially the threaded part, should be wiped frequently, and the lubricant that has been dirty by dust should be replaced with new ones, because the dust contains hard impurities, which can easily wear threads and the surface of the valve stem and affect its service life.

 

5. Maintenance of Valve Packing

Packing is directly related to whether the key seals leak when the valve is switched on or off. If the packing fails, the valve will be invalid, especially the valve of urea pipeline. Because of its high temperature, corrosive and harmful, the packing is easy to aging. Strengthened maintenance can prolong the life of fillers

Valves in the factory, in order to ensure the elasticity of fillers, usually static pressure test does not leak. After the valve is loaded into the pipeline, because of temperature and other factors, leakage may occur. At this time, it is necessary to tighten the nuts on both sides of the packing cover in time, as long as there is no leakage, and then the leakage is tightened again, so as not to tighten once, so as to avoid the loss of elasticity and sealing performance of the packing.

Some valve fillers are filled with molybdenum disulfide lubricating paste. When used for several months, the corresponding lubricating grease should be added in time. When the filler needs to be added, the corresponding filler should be added in time to ensure its sealing performance.

 

6. Maintenance of Valve Drive Parts

Valve in the process of switching, the original lubricating oil will continue to drain, coupled with temperature, corrosion and other factors, will also make the lubricating oil drying up. Therefore, the transmission part of the valve should be checked regularly, and the oil shortage should be filled in in time to prevent the increase of wear due to the lack of lubricant, resulting in transmission flexibility or jam failure and other faults.

 

7. Maintenance of valve during grease injection

When valve is injected with fat, the problem of the amount of fat injected is often neglected. After the greasing gun is refueled, the operator chooses the valve and the greasing connection mode, and then carries on the greasing operation. There are two situations: on the one hand, less grease injection and insufficient grease injection, and the sealing surface accelerates wear due to lack of lubricant. On the other hand, excessive fat injection causes waste. Because there is no accurate calculation of different valve sealing capacity according to the type and type of valve. Sealing capacity can be calculated by valve size and type, and a reasonable amount of grease can be injected.

Pressure is often neglected in valve grease injection. During the operation of lipid injection, the pressure of lipid injection varies regularly from peak to valley. The pressure is too low, the seal leaks or fails, the pressure is too high, the grease injection mouth is blocked, the inner grease of the seal is hardened or the seal ring is locked with the valve ball and the valve plate. Usually when the pressure of grease injection is too low, the grease injected into the bottom of the valve chamber, usually occurs in small gate valves. The pressure of grease injection is too high, on the one hand, check the grease injection nozzle, such as the identification of the blockage of the grease hole for replacement; on the other hand, lipid hardening, to use cleaning fluid, repeatedly soften the failed sealing grease, and inject new grease replacement. In addition, sealing type and sealing material also affect the grease injection pressure. Different sealing forms have different grease injection pressure. Generally, the grease injection pressure of hard seal is higher than that of soft seal.

When filling the valve with grease, pay attention to the problem of the valve at the switch position. Ball valve maintenance is generally in the open state, in special cases choose to close maintenance. Other valves cannot be treated as open valves. Gate valves must be closed during maintenance to ensure that grease fills the sealing grooves along the sealing ring. If opened, the grease falls directly into the runner or valve chamber, causing waste.

When valve is greased, the effect of grease injection is often neglected. The pressure, the amount of fat injected and the switch position are all normal in the operation of fat injection. However, in order to ensure the grease injection effect of the valve, sometimes it is necessary to open or close the valve, check the lubrication effect, and confirm that the surface of the valve ball or gate is lubricated evenly.

When injecting grease, attention should be paid to the problems of valve body sewage discharge and wire plugging and pressure relief. After the valve pressure test, the gas and water in the valve chamber of the sealing chamber will be pressurized due to the increase of ambient temperature. When injecting grease, it is necessary to discharge and relieve pressure first, so as to facilitate the smooth operation of injecting grease. After the grease injection, the air and water in the sealing chamber are fully replaced. Release the pressure of the valve chamber in time, which also ensures the safety of the valve. After the fat injection, we must tighten the blowdown and pressure relief wire to prevent accidents.

When injecting fat, we should pay attention to the problem of uniformity of fat. During normal lipid injection, the nearest lipid outlet from the lipid injection mouth first produces lipid, then to the low point, and finally to the high point, and then to the grease one by one. If it does not follow the rules or does not produce grease, it proves that there is blockage, and it should be cleared in time.

When injecting grease, we should also observe the problem of valve diameter and sealing ring seat leveling. For example, ball valves, if there is an open interference, can adjust the open limit inward, confirm that the path is straight and then lock. Adjusting the limit should not only pursue the position of opening or closing one side, but also consider it as a whole. If the opening is smooth and the closing is not in place, the valve will not be closed properly. Similarly, when adjustments are in place, corresponding adjustments should also be taken into account. Ensure the right-angle stroke of the valve

After fat injection, the mouth of fat injection must be sealed. Avoid impurities entering, or lipid oxidation at the lipid injection mouth. Cover with anti-rust grease to avoid rusting. So that it can be applied in the next operation.

When injecting grease, we should also consider the specific problems in the future oil sequential transportation. In view of the different quality of diesel oil and gasoline, the scouring and decomposition ability of gasoline should be considered. In the future valve operation, when encountering gasoline section operation, timely replenishment of grease to prevent wear and tear.

When greasing, do not neglect the grease injection at the stem position. There are sliding sleeves or fillers in the valve shaft, and it is also necessary to maintain lubrication to reduce the friction resistance during operation. If lubrication is not ensured, the torque of the wearing parts increases during electric operation, and the switch is laborious during manual operation.

Some ball valve bodies are marked with arrows. If there is no English FIOW handwriting attached, it will be the direction of the seating seat, not as a reference for the flow direction of the medium, and the direction of the valve self-discharge is the opposite. Typically, double seated ball valves have bidirectional flow direction.

When maintaining the valve, attention should also be paid to the problem of water intake in the electric head and its transmission mechanism. Especially in rainy season. One is to rust the transmission mechanism or the transmission shaft sleeve, and the other is to freeze in winter. When the electric valve is operated, the torque is too large, and the damage of the transmission parts will make the motor no-load or over-torque protection jump out and unable to realize the electric operation. The transmission parts are damaged and manual operation is not possible. Manual operation is also unable to switch after over-torque protection operation. If forced operation, internal alloy parts will be damaged.

Valve maintenance should be treated scientifically in order to achieve the proper effect and application of valve maintenance. In order to make the production work normally, reduce parking and increase economic benefits, we must do well in the aspect of valves.

1. Correct selection of valves is the foundation.

2. Correct use of valves is the key.

3. Correct maintenance is the guarantee.


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