The significance of correctly selecting valves

The correct selection of valves is crucial for ensuring the safe production of the device, improving the service life of the valve, and meeting the long-term operation of the device. The main cause of many valve accidents is improper valve selection, such as using cast iron valves in cold regions. Due to the accumulation of water in the oil in the valve body, the valve is prone to freezing and cracking during winter. In some pump outlet valves, due to certain reasons, small gate valves are often used to regulate flow in situations where the required process is low and the pump power is high. Due to the local opening of the gate valve plate, vibration occurs, accelerating the wear of the sealing surface between the gate plate and the valve seat, which can easily cause valve leakage. In addition, the quality of valves also has a significant impact on production and use. If a major explosion accident occurs in a fertilizer plant, the cause of the accident is identified as a liability accident caused by serious quality issues with the valve. The explosion reason is that the outlet valve of the second section cannot bear the normal working pressure and suddenly bursts, the check valve fails, and the 0.75 MPa half Water gas in the system quickly overflows, mixing with the surrounding air to form an explosive gas space, causing gas chemical explosion. According to testing, multiple indicators of the valve do not comply with relevant national standards. In addition, both of these are valves that use water, steam, and oil as media, and are dedicated to non combustible gases. The design department's selection was also incorrect. Therefore, the correct selection of valves is crucial for device production, safety, long-term operation, and improving efficiency. The principle of selecting valves for petrochemical production equipment should meet the following basic principles of reliability. Petrochemical production requires continuous, stable, and long-term operation. Therefore, it is required that the valves used should have high reliability and large Factor of safety, and major production safety and casualty accidents should not be caused by valve failure; Meeting the requirements of long-term operation of the device, long-term continuous production is the benefit; In addition, reduce or avoid "running, emitting, dripping, and leaking" caused by valves, create clean and civilized factories, and promote HSE management. To meet the requirements of process production, valves should meet the needs of operating medium, pressure, temperature, and usage, which is also the most basic requirement for valve selection. For example, if a valve is required to provide overpressure protection and discharge excess media, safety valves and overflow valves should be selected; If it is necessary to prevent medium backflow during operation, a check valve should be used; To automatically discharge condensate, air, and other non condensable gases continuously generated in steam pipelines and equipment, while also preventing the escape of steam, a drain valve should be selected. In addition, for corrosive media, corrosion-resistant materials such as valve bodies should be selected. Convenient operation, installation, maintenance, and repair. Once the valve is safe, it should enable the operator to correctly identify the valve direction, opening signs, and indication signals, facilitating timely and decisive handling of various emergency faults. Meanwhile, the structure of the selected valve type should be as simple as possible, and installation, maintenance and repair should be convenient. Economically, pay attention to saving investment and reducing device costs. Today's investment is tomorrow's cost. For general occasions, domestic production can meet the usage requirements and domestic valves should be selected; If several different valve types can meet the usage requirements, low-cost and structurally simple valves should be selected; Higher grade materials such as Cr Mo steel, stainless steel, babbitt alloy, etc. should not be used if the general material can meet the usage requirements.

Valves, like other mechanical products, also require maintenance and upkeep. If this work is done well, it can extend the service life of the valve. The following will introduce the maintenance and safekeeping of the valve

*The purpose of storage and maintenance is to prevent valve damage or reduce 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, while large valves can be neatly arranged on the warehouse floor. They should not be piled up or stacked randomly, and the flange connection surface should not come into contact with the ground. This is not only for the sake of aesthetics, but also to protect the valve from damage.

*Due to improper storage and handling, the handwheel is broken, the valve stem is tilted, and the fixing nut between the handwheel and the valve stem is loose and lost. These unnecessary losses should be avoided.

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

*For valves that have just entered the warehouse, they should be inspected. If rainwater or dirt enters during transportation, they should be wiped clean before being stored.

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

*The machined surface of valves that can rust in the atmosphere should be coated with anti rust oil to protect it.

*Valves placed outdoors must be covered with waterproof and dustproof items such as felt or tarpaulin. The warehouse storing valves should be kept clean, dry, and maintained for use

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

*The valve rod thread often rubs with the valve rod nut, and a little yellow dry oil, Molybdenum disulfide or graphite powder should be coated for lubrication.

*For valves that do not open and close frequently, it is also necessary to regularly rotate the handwheel and add lubricant to the valve stem threads to prevent seizing.

*For outdoor valves, a protective sleeve should be added to the valve stem to prevent rain, snow, dust, and rust.

*If the valve system is mechanically inactive, add lubricating oil to the gearbox on time.

*Always keep the valve clean.

*Regularly inspect and maintain the integrity of other components of the valve. If the fixed nut of the handwheel falls off, it should be matched and cannot be used properly, otherwise it will grind the four sides of the upper part of the valve stem, gradually losing the reliability of the fit, and even unable to start.

*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 regularly wiped. Lubricants that have been contaminated with dust should be replaced with new ones, as the dust contains hard debris that can easily wear the threads and valve stem surface, affecting the service life of the packing

*The packing is directly related to the key sealing components of whether leakage occurs when the valve is opened and closed. If the packing fails, causing leakage, the valve is also equivalent to failure, especially for valves in urea pipelines. Due to their high temperature, corrosion is more severe, and the packing is prone to aging. Strengthening maintenance can extend the lifespan of the filler.

*When the valve leaves the factory, in order to ensure the elasticity of the packing, it is generally based on static pressure testing without leakage. After the valve is installed in the pipeline, due to temperature and other factors, external leakage may occur. At this time, it is necessary to tighten the nuts on both sides of the packing gland in a timely manner, as long as there is no leakage. If there is any external leakage in the future, tighten it again, and do not tighten it all at once to prevent the packing from losing elasticity and sealing performance.

*Some valve packing contains Molybdenum disulfide lubricating paste. When it is used for several months, corresponding lubricating grease should be added in time. When it is found that the packing needs to be added, corresponding packing should be added in time to ensure its sealing performance. During the opening and closing process of the maintenance valve at the transmission part, the original added lubricating grease will continue to drain. In addition, temperature, corrosion and other factors will also make the lubricating oil dry. Therefore, the transmission part of the valve should be regularly inspected, and if oil shortage is found, it should be promptly replenished to prevent increased wear due to a lack of lubricant, resulting in inflexible transmission or jamming failure. Maintenance and upkeep of the valve during grease injection

*When injecting grease into valves, the issue of the amount of grease injected is often overlooked. After refueling the grease gun, the operator selects the valve and grease connection method before proceeding with the grease injection operation. There are two situations: on the one hand, the amount of grease injected is insufficient, and the sealing surface accelerates wear due to a lack of lubricant. On the other hand, excessive fat injection can cause waste. The reason is that the sealing capacity of different valves is not accurately calculated according to the valve type and category. The sealing capacity can be calculated based on the size and type of the valve, and an appropriate amount of lubricating grease can be injected reasonably.

*When injecting grease into valves, pressure issues are often overlooked. During the grease injection operation, the grease injection pressure exhibits a regular peak valley variation. If the pressure is too low, the seal leaks or fails, if the pressure is too high, the grease injection port is blocked, the grease inside the seal hardens, or the sealing ring is locked with the valve ball or valve plate. Usually, when the grease injection pressure is too low, the injected lubricating grease mostly flows into the bottom of the valve chamber, usually occurring 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; On the other hand, lipid hardening requires the use of cleaning fluid, repeated softening of failed sealing grease, and injection of new lubricating grease for replacement. In addition, the sealing model and sealing material also affect the grease injection pressure, and 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 issue of the valve being in the ON/OFF position. Ball valves are generally in the open position during maintenance, and in special circumstances, they should be closed for maintenance. Other valves cannot be treated solely as open positions. During maintenance, the gate valve must be in a closed state to ensure that the lubricating grease fills the sealing groove along the sealing ring. If it is opened, the sealing grease will directly fall into the flow channel or valve chamber, causing waste.

*When injecting grease into valves, the issue of grease injection effect is often overlooked. The pressure, grease injection volume, and switch position are all normal during the grease injection operation. However, to ensure the effectiveness of valve lubrication, it is sometimes necessary to open or close the valve and check the lubrication effect to confirm that the surface of the valve ball or gate is evenly lubricated.

*When injecting grease, attention should be paid to valve body drainage and plug pressure relief issues. After the valve pressure test, the gas and water in the sealing chamber valve chamber increase in pressure due to the increase in environmental temperature. When injecting grease, it is necessary to first discharge and relieve pressure to facilitate the smooth progress of the grease injection work. After grease injection, the air and water in the sealing chamber are fully replaced. Timely release of valve chamber pressure also ensures the safety of valve use. After the grease injection is completed, it is necessary to tighten the drain and pressure relief plugs to prevent accidents.

*When injecting fat, it is important to pay attention to the issue of even fat production. During normal grease injection, the grease outlet closest to the grease injection port first releases the grease, then to the low point, and finally to the high point, gradually releasing the grease. If it does not follow the rules or does not produce fat, it indicates the existence of blockage, and timely cleaning treatment should be carried out.

*When injecting grease, it is also necessary to observe the problem of the valve diameter being flush with the sealing ring seat. For example, for a ball valve, if there is an opening interference, the opening limiter can be adjusted inward to confirm that the diameter is straight and then locked. Adjusting the limit should not only focus on opening or closing one position, but also consider the overall situation. If the opening position is flush and cannot be closed in place, it will cause the valve to not close tightly. Similarly, when adjusting the closing position, it is also necessary to consider adjusting the opening position accordingly. Ensure the right angle travel of the valve.

*After grease injection, make sure to seal the grease injection port properly. Avoid impurities entering or lipid oxidation at the grease injection port, and apply anti rust grease to the cover to avoid rusting. So that it can be applied in the next operation.

*When injecting grease, it is also necessary to consider the specific treatment of specific issues in the future sequential transportation of oil products. Considering the different qualities of diesel and gasoline, the ability of gasoline to wash and decompose should be considered. In the future valve operation, when encountering gasoline section operation, timely supplement lubricating grease to prevent wear and tear from occurring

*When applying grease, do not ignore the grease on the valve stem. There is a sliding shaft sleeve or packing at the valve shaft, and it is also necessary to maintain lubrication to reduce friction resistance during operation. If lubrication cannot be ensured, the torque of the worn parts will increase during electric operation, and the switch will be laborious during manual operation.

*Some ball valves have arrows marked on their valve bodies. If there is no English FIOW script attached, it indicates the direction of the sealing seat and is not used as a reference for the flow direction of the medium. The valve's self draining direction is opposite. Normally, a double seat sealed ball valve has a bidirectional flow direction.

*When maintaining valves, attention should also be paid to the issue of water ingress in the electric actuator and its transmission mechanism. Especially the rainwater that seeps in during the rainy season. One is to rust the transmission mechanism or shaft sleeve, and the other is to freeze in winter. Causing excessive torque during the operation of the electric valve and damaging the transmission components can cause the motor to be unloaded or the overtorque protection to trip, making it impossible to achieve electric operation. The transmission components are damaged and manual operation is not possible. After the overtorque protection action, manual operation is also unable to switch, and forced operation will damage the internal alloy components.

Valve maintenance should be treated with a scientific attitude in order to achieve the expected results and application goals of valve maintenance work. To ensure normal production operation, reduce parking, and increase economic benefits, it is necessary to do these three things well in terms of valves.