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2022

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08

Valve Operation and Maintenance Manual

Author:


Manual valves are a type of valve commonly used in equipment and devices. They are operated by handles and handwheels. Generally speaking, clockwise rotation of the handle and handwheel is designated as the closing direction, and counterclockwise rotation is designated as the opening direction. However, the opening and closing direction of some valves is opposite to the above, so you should check the opening and closing signs before operation.

1. Correct operation of manual valves

Manual valves are a type of valve commonly used in equipment and devices. They are operated by handles and handwheels. Generally speaking, clockwise rotation of the handle and handwheel is designated as the closing direction, and counterclockwise rotation is designated as the opening direction. However, the opening and closing direction of some valves is opposite to the above, so you should check the opening and closing signs before operation.

 

For manual valves, the size of the handle and handwheel are designed according to normal manpower. Therefore, there are regulations on the use of valves: operators are not allowed to use levers and long wrenches to open and close the valve. At the same time, if the handle length and handwheel diameter are less than 320mm, only one person can operate it; if the handwheel diameter is equal to or exceeds 320mm, two people can operate it together, or one person can operate it with the help of an appropriate lever (generally the length does not exceed 0.5m). . However, it is strictly prohibited to use levers or long wrenches to operate diaphragm valves and non-metallic valves, and it is 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 cause premature damage to the valve and even cause an accident. Practice has proven that, except for the impact handwheel, operating the valve too hard or too hard can easily damage the handwheel and handle, scratch the valve stem and sealing surface, or even crush the sealing surface. Secondly, if the handwheel or handle is damaged or lost, it should be replaced in time. It is not allowed to use an adjustable wrench as a substitute.

 

Valves such as gate valves and stop valves should be rotated 1/4 to 1/2 turns when closed or opened to the end (i.e. bottom dead center or top dead center) to make the threads more tightly sealed to facilitate inspection during operation and avoid twisting. Too tight and damage the valve.

Some of the larger diameter butterfly valves, gate valves and globe valves 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.

Before opening the steam valve, the pipeline must be preheated and the condensate water must be discharged. 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 rotates 90 degrees to the left or right. When the groove is perpendicular to the channel, it indicates that the valve is in the fully closed position. Some ball valves, butterfly valves, and plug valves are opened when the wrench is parallel to the channel, and closed when the wrench is vertical. The operation of three-way and four-way valves should be carried out according to the opening, closing and reversing marks. After the operation is completed, the movable handle should be removed.

For gate valves and throttle valves with scales, the fully open or fully closed indicating position should be checked and adjusted. Rising stem gate valves and globe valves should also remember their fully open and fully closed positions to avoid hitting the dead center when fully open. When the valve is fully closed, you can use the ruler and marks to find that the closing part has fallen off or is resisting foreign objects, so that you can troubleshoot.

Newly installed pipelines and equipment have a lot of dirt, welding debris, etc. inside. Dirt is easy to stick to the sealing surface of the normally open manual valve. The slightly open method should be used to allow the high-speed medium to wash away these foreign objects, and then close gently.

After some manual valves are closed, the temperature drops and the valve parts shrink, causing small gaps in the sealing surface and leakage. This should be done after closing and then closing again at the appropriate time.

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


    2. Precautions when operating valves

The process of operating the valve is also the process of inspecting and treating the valve. However, the following matters should be noted when operating the valve.

 

①High temperature valve. When the temperature rises above 200°C, the bolts will elongate due to heat, which may easily cause the valve to become loosely sealed. At this time, the bolts need to be "heat-tightened". It is not advisable to do it in the fully closed position of the valve during hot-tightening to avoid the valve stem from being pushed hard and making it difficult to open later.

② In seasons when the temperature is below 0°C, for valves that stop steam and water, be sure to open the valve seat plug to remove condensation and accumulated water to avoid freezing and cracking the valve. For valves that cannot remove accumulated water and valves that work intermittently, attention should be paid to thermal insulation.

③ The packing gland should not be pressed too tightly, and the valve stem should be operated flexibly (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). Without protective measures, do not replace or add packing at will under pressure.

④ During operation, you must carefully analyze the causes of abnormal phenomena discovered through listening, smelling, seeing, touching, etc., and eliminate them in time if you need to solve them yourself; if you need a repairman to solve them, do not force yourself to make do, so as not to delay the repair opportunity.

⑤ Operators should keep special logs or record books to record the operation of various valves, especially some important valves, high temperature and high pressure valves and special valves, including their transmission devices. Their faults, treatment methods, replacement parts, etc. should be recorded. These materials are very important to the operators themselves, repair personnel and manufacturers. Establishing a special log with clear responsibilities will help strengthen management.


    3. Valve storage and maintenance

The purpose of storage and maintenance is to prevent the valve from being damaged or reducing quality 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 randomly, and the flange connection surface should not be allowed to touch the ground. This is not only for aesthetics, but also to protect the valve from damage.

Due to improper storage and transportation, 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 the short term, the asbestos filler should be removed to avoid electrochemical corrosion and damage to the valve stem.

Valves that have just been put into storage must be inspected. If rain or dirt has entered during transportation, they must be wiped clean before storage.

The inlet and outlet of the valve should be sealed with wax paper or plastic sheet to prevent dirt from entering.

The processing surfaces of valves that can rust in the atmosphere should be coated with anti-rust oil to protect them.

Valves placed outdoors must be covered with rainproof and dustproof materials such as linoleum or tarpaulin. The warehouse where valves are stored must be kept clean and dry.


    4. Valve use and maintenance

The purpose of maintenance is to extend the service life of the valve and ensure reliable opening and closing.

 

The thread of the valve stem often rubs against the valve stem nut. A little yellow dry oil, molybdenum disulfide or graphite powder should be applied for lubrication.

For valves that are not frequently opened and closed, the handwheel should be turned regularly and lubricant should be added to the valve stem thread to prevent seizure.

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 inactive, lubricating oil must be added to the gearbox on time.

Always keep the valve clean.

Always check and maintain the integrity of other valve components. If the fixing nut of the handwheel falls off, it must be matched and cannot be used randomly. Otherwise, the upper part of the valve stem will be worn in all directions, gradually losing the reliability of the fit, and even being unable to operate.

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 contaminated by dust should be replaced with new one, because the dust contains hard debris, which can easily wear the threads and the valve stem surface, 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 opens and closes. If the packing fails and causes leakage, the valve will also fail. Especially for the valves of the urea pipeline, because of its relatively high temperature, corrosion is more serious, and the packing is prone to aging. Enhanced maintenance can extend the life of the filler

 

When the valve leaves the factory, in order to ensure the elasticity of the packing, it is generally subject to a static pressure test without leakage. After the valve is installed in the pipeline, extravasation may occur due to factors such as temperature. At this time, it is necessary to tighten the nuts on both sides of the packing gland in time, as long as there is no leakage. If extravasation occurs in the future, tighten it again, not once. Tighten tightly to prevent the filler from losing elasticity and sealing performance.

Some valve packings are filled with molybdenum disulfide lubricating paste. After several months of use, the corresponding lubricating grease should be added in time. When it is found that the packing needs to be added, the corresponding packing should be added in time to ensure its sealing performance.


    6. Maintenance of valve transmission parts

During the opening and closing process of the valve, the originally added lubricating grease will continue to be lost, and coupled with the effects of temperature, corrosion and other factors, the lubricating oil will continue to dry up. Therefore, the transmission part of the valve should be checked frequently, and if there is a lack of oil, it should be replenished in time to prevent increased wear due to lack of lubricant, resulting in inflexible transmission or stuck failure.


    7. Maintenance during valve grease injection

When filling valves with grease, the amount of grease is often overlooked. After refueling the grease gun, the operator selects the valve and grease injection connection method before performing the grease injection operation. There are two situations: on the one hand, the amount of grease injected is small and insufficient, and the sealing surface wears faster due to lack of lubricant. On the other hand, excessive fat injection causes waste. The reason is that there is no comprehensive calculation of the sealing capacity of different valves according to the valve type category. The sealing capacity can be calculated based on the size and type of the valve, and then the appropriate amount of grease can be injected reasonably.

 

When greasing valves, pressure issues are often ignored. During the grease injection operation, the grease injection pressure changes regularly between peaks and valleys. If the pressure is too low, the seal will leak or fail; if the pressure is too high, the grease injection port will be clogged, the grease inside the seal will harden, or the sealing ring will be 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 nozzle and replace it if the grease pores are blocked; on the other hand, if the grease is hardened, use cleaning fluid to repeatedly soften the failed sealing grease and inject new grease to replace it. . In addition, the seal model and seal material also affect the grease injection pressure. Different seal forms have different grease injection pressures. Generally, the grease injection pressure of hard seals is higher than that of soft seals.

 

When greasing the valve, pay attention to the problem of the valve in the switch position. Ball valves are generally kept in the open position during maintenance, and may be closed for maintenance under special circumstances. Other valves cannot be regarded as open. The gate valve must be closed during maintenance to ensure that the grease fills the sealing groove along the sealing ring. If it is open, the sealing grease will fall directly into the flow channel or valve cavity, causing waste.

When the valve is greased, the issue of grease injection effect is often ignored. During the grease injection operation, the pressure, grease injection amount, and switch position are all normal. 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 plate is evenly lubricated.

When injecting grease, attention should be paid to valve body drainage and plug pressure relief. After the valve pressure test, the gas and moisture in the sealed cavity valve cavity will increase in pressure due to the increase in ambient temperature. During grease injection, the sewage and pressure must be discharged first to facilitate the smooth progress of the grease injection work. After grease injection, the air and moisture in the sealed cavity are fully replaced. Timely release of valve cavity pressure also ensures the safety of the valve. After greasing, be sure to tighten the drain and pressure relief plugs to prevent accidents.

When injecting grease, pay attention to the issue of uniform grease dispensing. During normal grease injection, the fat outlet hole closest to the grease injection port will be greased out first, then to the lowest point, and finally to the high point, and the grease will be output one by one. If it does not follow the rules or does not produce fat, it proves that there is a blockage and needs to be cleared in time.

 

When injecting grease, you should also observe that the valve diameter is flush with the sealing ring seat. For example, in a ball valve, if there is opening interference, the opening limiter can be adjusted inward and locked after confirming that the diameter is straight. When adjusting the limit, you should not just pursue the open or closed position, but consider the overall position. If the opening position is flush and the closing position is not in place, the valve will not close tightly. In the same way, when adjusting the closing position, the corresponding adjustment of the opening position should also be considered. Ensure right angle travel of the valve.

After grease injection, be sure to seal the grease injection port. To avoid the entry of impurities or the oxidation of the lipid at the grease injection port, the cover should be coated with anti-rust grease to avoid rust. So that it can be applied in the next operation.

When injecting grease, we should also consider specific issues in the sequential delivery of oil products in the future and deal with them in detail. Given the different qualities of diesel and gasoline, the scour and decomposition capabilities of gasoline should be considered. In the future valve operation, when encountering gasoline section operations, replenish grease in time to prevent wear and tear.

When injecting grease, do not ignore the grease in the valve stem. There is a sliding sleeve or packing on the valve shaft, which also needs to be kept lubricated to reduce frictional resistance during operation. If lubrication cannot be ensured, the torque will increase during electric operation and the worn parts will require laborious switching during manual operation.

 

Some ball valve bodies are marked with arrows. If there is no English FIOW, it is the direction in which the sealing seat acts, and is not used as a reference for the flow direction of the medium. The self-discharging direction of the valve is opposite. Typically, double-seat sealed ball valves have bidirectional flow.

When maintaining the valve, attention should also be paid to the problem of water intrusion in the electric head and its transmission mechanism. Especially the rainwater that seeps in during the rainy season. One is that the transmission mechanism or transmission sleeve will rust, and the other is freezing in winter. As a result, the torque is too large when the electric valve is operated, and damage to the transmission components will cause the motor to be unloaded or the over-torque protection will trip, making it impossible to realize electric operation. The transmission parts are damaged and manual operation is impossible. After the over-torque protection action, manual operation is also unable to switch. Forcible operation will damage the internal alloy components.

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 downtime and increase economic benefits, these three points must be done in terms of valves:
    1. The correct selection of valves is the foundation.
    2. Correct use of valves is the most critical.
    3. Proper maintenance is the guarantee.