【Weekly Topic】Production Technology: What are the precautions for using valves? 2011.07.03~. 7.10

1. Select the appropriate valve, material, pressure rating, sealing surface, and handle orientation. 2. The valve should be opened and closed evenly; do not open or close it abruptly. Gate valves and globe valves require an F wrench; pay attention to the correct usage method. 3. Take care of the bolts of the valve to prevent rusting. 4. When replacing the gasket, the sealing surface must be cleaned thoroughly to prevent leaks. 5. When disassembling and assembling valves, bolts must be tightened symmetrically to prevent uneven tightening. 6. Sequence for removing bolts when disassembling the valve.

This post was last edited and replied to by Refinery Operator on 2011-7-3 at 11:00. 1# sun-rock: Fluoroplastic-lined anti-corrosion valves have been widely used in devices in industries such as petroleum, chemicals, pharmaceuticals, metallurgy, and power that are exposed to highly corrosive substances like acids and alkalis. However, regarding how to select and use such valves properly, based on the many years of field experience of our customers, the following considerations should be taken into account when choosing fluoroplastic-lined anti-corrosion valves, including factors such as the temperature, pressure, and pressure difference of the medium: 1. Temperature of the medium used with fluoroplastic-lined valves: All types of fluoroplastic-lined valves produced by our company use F46 (FEP) as the fluoroplastic material. The temperature of the medium used cannot exceed 150°C; although the temperature can reach 150°C for short periods of time, it should be kept below 120°C during prolonged use. Otherwise, the F46 material lining the various components of the valve may soften and deform, resulting in the valve not being able to close properly and causing significant leakage. If the temperature of the medium in use is below 180°C for short periods of time and below 150°C for longer periods, another type of fluoroplastic—PFA—can be used; however, PFA-lined components are more expensive than those lined with F46. 2. There should be no negative pressure. Fluoroplastic-lined valves should not be used in pipelines with negative pressure, as such pressure can cause the fluoroplastic lining inside the valve to be pulled out or peeled off, leading to problems with the valve’s opening and closing functions. 3. Pressure and pressure difference should be kept within the allowable range. In particular, fluoroplastic-lined control valves and globe valves with bellows seals. Since the bellows are made of PTFE material, high pressures and pressure differences can easily cause the bellows to rupture. Fluoroplastic control valves with bellows seals can be equipped with PTFE packing seals in applications where high pressures and pressure differences are present. 4. The medium used in fluoroplastic-lined valves should not contain hard particles, crystals, impurities, etc., to prevent wear of the fluoroplastic lining on the valve core, valve seat, or PTFE bellows during opening and closing operations. For media containing hard particles, crystals, or impurities, Hastelloy can be used for the valve core and valve seat. 5. For fluoroplastic control valves, the diameter of the valve should be selected appropriately based on the required flow rate (CV value). When selecting a valve, it is necessary to calculate the appropriate diameter and opening degree of the valve based on technical parameters such as the required flow rate (CV value). If the valve diameter is chosen to be too large, the valve will inevitably operate at a low opening degree for extended periods. Combined with the pressure of the medium, this can cause the valve’s core and stem to be subjected to impacts from the medium, resulting in vibration in the valve. Over time, such exposure to impacts can even lead to the breakage of the valve stem. When selecting various fluoroplastic-lined valves, users should strive to understand and master the technical requirements for their use, so as to make the right choices, make proper use of them, and extend their service life. In cases where conditions exceed the applicable technical limits, the manufacturer should be consulted to jointly discuss and implement appropriate measures for resolution. Forged steel low-temperature valves need to be addressed on a case-by-case basis in regard to the specific issues that arise during future sequential oil transportation. Given the different properties of diesel and gasoline, the scouring and decomposition capabilities of gasoline should be taken into account. In future valve operations, when working in the gasoline section, replenish lubricant in a timely manner to prevent wear. When injecting grease, do not neglect greasing the valve stem area. The valve shaft area, which features sliding bushings or packing, also needs to be kept lubricated in order to reduce frictional resistance during operation. If lubrication is not ensured, increased torque occurs during electric operation, leading to wear of the components, while manual operation becomes more difficult.

This post was last edited and replied to by Refinery Operator on 2011-7-3 11:02. Reply 1# sun-rock: Inspections to be carried out before using the valve. The inspection items include: 1. Checking for defects such as sand holes and cracks on the inner and outer surfaces of the valve body； 2. Is the seat firmly attached to the valve body? Do the valve stem and seat match properly? Are there any defects on the sealing surface? ； 3. Whether the connection between the valve stem and the valve core is flexible and reliable; whether the valve stem is bent; whether there is any damage or corrosion on the threads ； 4. Are the fillers and washers aged or damaged? ； 5. Whether the valve opens smoothly, etc. V. Common problems that occur during the use of valves 1. Leakage at the flanges and threads connecting to the pipes ； 2. Leakage at the filler box, leakage at the gasket, and inability to move the valve stem ； 3. Poor sealing between the valve core and the valve seat causes internal leakage. VI. Characteristics of commonly used valves in the chemical industry and precautions for their use
(1) Plug valves (cocks)
Characteristics: When the temperature is below 150°C and the pressure is less than 1.6 MPa, these valves feature a simple structure, rapid opening/closing, easy operation, and low fluid resistance.
Precautions for use:
1. The outer end of the valve stem is square-shaped. A line marked along its diagonal indicates that when this line is perpendicular to the valve body, the valve is in the closed state; when it aligns with the direction of the valve body, the valve is in the open state ； 2. Use a special wrench for cocks to operate valves normally, to prevent slipping on the valve stem and resulting in safety accidents ； Try to avoid using adjustable wrenches, as this can cause slipping ； 3. Open the valve and conduct the inspections outlined earlier; after the inspection is complete, slowly open the valve. Try not to stand in the direction of the sealing surface when doing this, and wear an acid-resistant mask when dealing with acidic or alkaline fluids ； (II) Ball valve: The ball valve belongs to the same category as the plug valve; the only difference is that its closing element is a sphere with a hole through it, and the sphere rotates around the axis of the valve stem to achieve opening and closing. Jacketed insulated ball valve, stainless steel ball valve, quick-opening ball valve. Features: Simple valve structure, reliable operation; suitable for pipelines with bidirectional flow of media, low fluid resistance, and good sealing performance ； Disadvantage: The medium can easily leak from the valve stem area. Precautions for use: The same as those for ball valves ； For valves with a handle, when the handle is perpendicular to the direction of the medium flow, the valve is in the closed state; when it aligns with that direction, the valve is in the open state ； When encountering ball valves with jacketed insulation, the following points should be noted: The steam supply for the jacket insulation should be turned on to melt any medium that tends to crystallize inside the valve before attempting to open or close it; never try to open or close the valve until the medium has been completely melted ； When a valve fails to open, it is not advisable to use a longer lever arm to force it open, as this can cause the valve stem to encounter excessive resistance and lead to the separation of the valve core, resulting in damage to the valve or to the wrench itself, and thus creating safety hazards. (III) Butterfly Valve: A butterfly valve uses a disc that can rotate around an axis to control the opening and closing of a pipeline, with the degree of rotation indicating the extent to which the valve is open. Depending on the actuation method, butterfly valves are divided into manual, pneumatic, and electric types; the manual type is the most commonly used, with a rotating handle driving the valve stem through gear transmission to open and close the valve. Features: Butterfly valves have advantages such as simple structure, relatively quick opening and closing, low fluid resistance, and easy maintenance. However, they cannot be used in high-temperature and high-pressure environments; they are suitable for large-diameter pipelines carrying water, steam, air, oil, and similar fluids under conditions where PN is less than 1.6 Mpa and t is below 120 degrees. Precautions for use: 1. The valve core can only rotate 90 degrees; the directions of the CLOSE and OPEN arrows are usually indicated on the valve body. Turning the handwheel clockwise closes the valve, while turning it counter-clockwise opens it ； 2. If there is some resistance when opening or closing the valve, a special F-wrench can be used to operate it. However, do not force it open or closed, as this may damage the valve stem gears ； 3. It is prohibited to remove the handwheel and use an adjustable wrench to turn the valve stem ； (The same applies to the valve below.) 4. Open and close it gradually, observe for any abnormalities, and prevent leaks. (IV) Globe valve: The globe valve is the most widely used type of shut-off valve in chemical production. Unlike the three aforementioned types of shut-off valves, it does not rely on the rotation of its closing element to open or close; instead, the upward and downward movement of the valve stem drives a circular valve disc (valve head) connected to it, thereby changing the distance between the disc and the valve seat to control the opening and closing of the valve. Features of streamlined globe valves and American standard globe valves: These valves have a handwheel and valve stem at the upper part; the middle section contains threads and a packing seal. In smaller valves, the threads on the valve stem are located inside the valve body, giving them a compact structure. However, the part of the valve stem that comes into contact with the medium is extensive, and the threaded area is particularly prone to corrosion. The complexity of the valve’s structure can be determined by the height at which the valve stem protrudes from the valve cover. Despite this complexity, these valves are easy to operate and do not require much effort; they allow for easy regulation of flow rate and closure of the flow path. Their operation is slow, without any water hammer effect, which is why they are widely used. When installing a stop valve, attention must be paid to the flow direction of the fluid; the fluid in the pipeline should flow from below upward through the valve seat, following the principle of \"flowing in from below and out from above\". This is done to reduce fluid resistance, make it easier to open the valve, and ensure that the valve stem and packing components do not come into contact with the medium when the valve is closed, thereby preventing damage to these components and avoiding leaks. Stop valves are primarily used in pipelines for water, steam, compressed air, and various materials; they allow for precise regulation of flow rates and effective closure of the flow path, but they cannot be used with materials that are highly viscous or prone to crystallization. Precautions for use: 1. Before turning it on, check the valve for any defects, especially to ensure there is no leakage in the packing gland ； 2. When the valve stem cannot be rotated manually, a specialized F-wrench can be used to open and close it. If it is still not possible to do so, do not try to force the opening or closing by increasing the length of the wrench’s lever arm, as this may cause damage to the valve or lead to safety accidents ； 3. When used in valves for medium-pressure steam pipelines, it is necessary to first drain all the condensate water from within the pipeline before opening the valve. Then, the valve should be opened slowly, and steam at a pressure of 0.2 to 0.3 Mpa should be used to preheat the pipeline, in order to avoid damage to the sealing surfaces caused by sudden pressure increases. Once everything is checked and found to be normal, the pressure can be adjusted to the desired level ； (5) Gate valve: Also known as a knife gate valve or sluice valve, it controls the opening and closing of the valve by raising or lowering a gate. The gate is perpendicular to the direction of the fluid flow; altering the relative position between the gate and the valve seat changes the size of the passageway. Rising-stem gate valves and non-rising-stem gate valves. Based on the manner in which the valve stem moves during opening and closing, gate valves can be categorized into rising-stem and non-rising-stem types. In a rising-stem gate valve, the threads of the stem are exposed outside the valve body; when the valve is opened, the stem extends beyond the handwheel. Its advantages are that the degree of valve opening can be determined based on the length of the extended stem, and the length of the stem in contact with the medium is relatively short, so the threaded portion is largely unaffected by corrosion from the medium. The drawback is that it requires a considerable amount of vertical space for this extension. In a non-rising stem gate valve, the threads on the valve stem engage with the internal threads on the gate from within the stem. When the valve is opened, the stem merely rotates without moving up or down, while the gate rises along the stem threads. The advantage of the dark-stem gate valve is its small external projection, while the disadvantage is that it is not possible to determine whether the valve is open based on the condition of the stem; moreover, the threads on the stem are exposed to the medium for extended periods and are prone to corrosion. Gate valves have advantages such as low fluid resistance, constant flow direction of the medium, slow opening without water hammer effect, and easy flow regulation. However, their disadvantages include complex structure, large size, long opening and closing times, and difficulty in maintaining the sealing surfaces. In large-diameter water supply pipes 1, once the valve stem has reached its open or closed position, further force should not be applied, as this may break the internal threads or pin screws and damage the valve ； 2. When it is not possible to operate the valve directly by hand, an F-wrench can be used to open or close it ； 3. When opening and closing the valve, pay attention to the valve’s sealing surface, especially the packing gland, to prevent leaks. (VI) Throttle valve: The throttle valve, also known as a needle valve, has a shape similar to that of a globe valve; however, its valve element is different in shape, being conical or parabolic. It is commonly used in chemical instrumentation and is usually connected via threads. Precautions for use: 1. Due to the threaded connection, check first whether the thread connection is loose or leaking when opening and closing ； 2. Operate the valves slowly when opening and closing them, as the flow area is small and the flow velocity is high, which may cause corrosion of the sealing surfaces. Pay close attention and monitor any changes in pressure. (7) Check valve: A check valve is a valve that opens and closes automatically due to the pressure difference between the medium on either side of it, thereby controlling the one-way flow of the medium; it is also known as a non-return valve or one-way valve. Based on their structure, check valves are divided into lift-type (poppet type) and swing-type (rotary disc type). Lift-check type: Precautions for use: Pay attention to the valve orientation; the arrow should point in the same direction as the flow of the medium. If the medium is prone to crystallization, it may prevent the valve disc from being depressed, thus rendering the valve ineffective as a control or check valve. (8) Safety valve: A safety valve is a type of valve that opens and closes automatically based on the pressure of the medium. When the pressure exceeds a set value, it opens automatically to release pressure and prevent damage to the equipment and pipelines; it then closes automatically once the pressure returns to normal. Based on the method of balancing internal pressure, safety valves are divided into lever-pendulum type and spring type. Precautions for use: 1. Safety valves must be used within the valid period of verification ； 2. The safety valves and control valves installed on pipelines and equipment are usually globe valves, which must be opened to ensure that the safety valves can function effectively ； 3. Periodically lift the valve disc slightly and use the medium to blow away impurities inside the valve. 4. If the safety valve cannot operate at the set pressure, it must be re-tested or replaced. (IX) Trap: A trap is a valve that enables automatic intermittent removal of condensate from steam pipelines, heaters, and other equipment systems, while also preventing steam leakage. The commonly used types include bell float type, thermodynamic type, and pulse type. Precautions for use: 1. Before use, drain any condensate using the pipe bypass valve. When steam is present, close the bypass and activate the main path of the steam trap; otherwise, water will accumulate inside the valve, rendering it ineffective at draining steam ； 2. Be careful not to get scalded by steam when opening and closing the valves. (10) Various types of sampling valves. As the name implies, sampling valves are used to obtain samples of a medium so that chemical analysis can be performed on them. They are generally installed on equipment or pipelines and can be roughly divided into the following types: double-acting valve, flange-clamped valve, and sampling valve with an insulation jacket ； Usage precautions: 1. A double-operation valve generally consists of two ball valves; it ensures sampling safety and enables sampling in negative-pressure systems through coordinated operation ； When taking a sample, first close the second valve located near the equipment and piping, then open the first valve to allow the medium to flow into the space between the two valves ； Then close the first valve, open the second valve, and place the sampling vessel at the sampling port to contain the medium ； 2. Generally, flange clip valves are sealed by means of the cone at the top of the valve stem and the conical hole in the valve seat. During sampling, rotating the handwheel disengages the valve stem from the conical hole, allowing the medium to flow from the conical hole into an external sampling vessel ； 3. For sampling valves with jacketed insulation, the following points should be noted: The steam for jacket insulation should be turned on to melt the medium that tends to crystallize inside the valve before attempting to open or close it; never try to open or close the valve until the medium has been completely melted ； When a valve cannot be opened, it is not permissible to use a longer lever arm to force it open, as this can lead to the valve stem encountering excessive resistance and causing the valve core to come loose, or it can damage the sealing surface between the valve stem and the tapered hole. This may result in damage to the valve or to the wrench, creating safety hazards. (11) Fluoroplastic-lined valves: Fluoroplastic-lined valves are primarily used in corrosive media such as acids and bases. Their structural principle is similar to that of valves without fluoroplastic lining; the difference lies in the fact that their valve stems, valve cores, and valve seats are all lined with fluoroplastic. Their method of use is similar as well.

Precautions for using valves: 1. Identify the valve opening/closing direction: Generally, for manual valves, turning clockwise closes them, while turning counterclockwise opens them; however, there are exceptions where this is reversed. The stem of the 90° turning plug valve has a groove (margine) at its top; it is closed when perpendicular to the pipeline and open when parallel to the pipeline. When switching pneumatic or electric valves to manual operation, attention should be paid to the direction-changing and on/off indicators on them ； 2. Use appropriate force; never use a large wrench to operate small valves ； 3. When there is a large temperature difference on both sides of the valve, drain the water from the pipe first and then open it slowly. When the pressure difference between the two sides is too large, the bypass valve must be opened first before opening the main valve ； 4. When opening or closing gate valves and globe valves to the extreme, turn them 1/4 to 1/2 turn to avoid over-tightening, which could damage the valve components, or prevent the valve from operating after being exposed to heat or cold. 5. For pneumatic valves with handwheels, the handwheel should normally be in the middle position (automatic mode) to avoid interfering with the pneumatic operation. In the event of a pneumatic failure, manual operation using a handwheel can be carried out on-site.

1. What is the medium flowing inside the valve, and what are the operating conditions of this medium: including temperature, flow rate, pressure, etc.? These differences may lead to variations in the methods of use and maintenance, as well as the time required, etc ； 2. Are there any special requirements for this valve in terms of processing, such as the KV value? Will its use over time affect the processing process? If so, maintenance will be necessary ； 3. Ensure that the medium flowing in from the upstream side meets the requirements for passing through the valve; for example, some requirements pertain to particle size and dust levels, while others prohibit the presence of gas-liquid mixtures, etc ； 4. Conduct regular inspections in accordance with the valve manufacturer’s guidelines or the instructions manual, and prepare a maintenance kit in advance to be prepared for any issues.

1. When opening or closing valves, turn them back half a turn once they reach the desired position to avoid overturning. 2. Avoid using an F wrench to turn the valve on and off with excessive force. 3. Regularly lubricate the valve stem for maintenance. 4. Gate valves are not allowed to be used for regulating medium flow rate. 5. If it is necessary to adjust the flow rate for the valves on high-pressure pipelines, install one regulating valve and keep all the others fully open, in order to prevent internal leakage in the valves due to prolonged use. 6. Valves with a large pressure difference between the inlet and outlet require a balance valve.

Regular inspections should be carried out, with the main inspection items being: (1) Wear condition of the sealing surfaces. 　　(2) Wear condition of the trapezoidal threads on the valve stem and valve stem nut. 　　(3) Check whether the filler is outdated or ineffective; if damaged, it should be replaced promptly. 　　(4) After the valve has been overhauled and assembled, a sealing performance test should be conducted.

1. During use, turn it on slowly. 2. Choose the correct model during installation. 3. When the valve is slightly blocked, use a gate valve. 4. Pay attention to the valve direction; many valves have a specific orientation, and using the wrong direction can lead to serious problems.

Reply 1# sun-rock: For valves, one not only needs to know how to install and maintain them, but also how to operate them. I. Opening and closing of manual valves Manual valves are the most widely used type of valves. Their handwheels or handles are designed to be operated using normal human strength, taking into account the strength of the sealing surfaces as well as the necessary force required for closing. Therefore, it cannot be turned using a long lever or long wrench. Some people* are used to using wrenches, and they must be careful not to apply excessive force, as this can easily damage the sealing surfaces or break the wrench, the wheel, or the handle. When opening or closing the valve, apply force smoothly without any impact. The various components of certain high-pressure valves that are operated by impact have taken this type of impact force into account, as it is different from that in ordinary valves. For steam valves, they should be preheated and of the condensed water should be removed before opening. The valve should be opened as slowly as possible to avoid water hammer. After the valve is fully open, turn the handwheel slightly in the opposite direction to ensure a tight fit between the threads, thereby preventing loosening and damage. For straight-stem valves, remember the position of the stem when the valve is fully open and fully closed, to avoid hitting the dead center when it is fully open. It also facilitates checking whether it is functioning properly when fully closed. If the valve seat comes loose, or large debris gets trapped between the valve core seals, the position of the valve stem when the valve is fully closed will change. When the pipeline is used for the first time, it contains a lot of dirt inside. The valve can be slightly opened to allow the high-speed flow of the medium to carry away this dirt, after which it should be closed gently (it must not be closed quickly or forcefully to prevent residual impurities from damaging the sealing surfaces). The valve should then be opened again, and this process repeated several times until all the dirt is removed, after which normal operation can resume. For normally open valves, dirt may be stuck on the sealing surface; when closing them, it is necessary to clean them using the aforementioned method before closing them properly. If the handwheel or handle is damaged or lost, it must be replaced immediately; adjustable wrenches should not be used as a substitute, as this may damage the square shape of the valve stem, resulting in poor operation of the valve and potential accidents during production. In some media, cooling after the valve is closed causes the valve components to contract; therefore, the operator should close it again at an appropriate time to ensure that no gaps remain in the sealing surfaces. Otherwise, the medium will flow rapidly through these gaps, easily eroding the sealing surfaces. During operation, if it is found that the task is too difficult to carry out, the reasons should be analyzed. If the packing is too tight, it can be loosened slightly; if the valve stem is skewed, personnel should be notified for repair. In some valves, when in the closed state, the closing element expands due to heat, making it difficult to open. If it is necessary to open the valve at this time, loosen the valve cover threads by half a turn to one full turn to relieve stress on the valve stem, and then turn the handwheel. II. Precautions for the installation and use of valves 1. For high-temperature valves operating at temperatures above 200°C, since they are installed at room temperature, the temperature rises during normal operation, causing the bolts to expand due to heat and increasing the gaps between them. Therefore, it is necessary to tighten them again; this process is known as “thermal tightening”. Operators must pay attention to this step, as failure to do so can lead to leaks. 2. When the weather is cold and the water valve remains closed for an extended period, any accumulated water behind the valve should be drained. After the steam valve stops supplying steam, the condensate also needs to be drained. There is a plug at the bottom of the valve, which can be opened to drain water. 3. Non-metallic valves: some are hard and brittle, while others have lower strength. When operating them, the force used for opening and closing should not be too great, especially violent force should be avoided. Be careful to avoid the objects from being bumped. 4. When using a new valve, do not compress the packing too tightly; just enough to prevent leakage. This is to avoid excessive pressure on the valve stem, which could accelerate wear and make it difficult to open and close the valve. The quality of valve installation has a direct impact on the performance of marine valves; therefore, great attention must be paid to the direction and position of the valves, the valve installation process, the protective measures for the valves, bypass systems and instruments, as well as the replacement of valve packing. (1) Direction and position: Many valves are directional, such as globe valves, throttle valves, pressure relief valves, check valves, etc. If installed in the wrong direction, it will affect their performance and lifespan (as in the case of throttle valves), or they may not function at all (as in the case of pressure relief valves), or it could even pose a danger (as in the case of check valves). For ordinary valves, there are direction indicators on the valve body; if not, they should be identified correctly based on the valve’s operating principle. The valve chamber of the stop valve is asymmetrical on the left and right; the fluid must flow through the valve orifice from bottom to top, which results in low fluid resistance (due to the shape of the valve). It is easier to open the valve as the medium pressure acts upward, and once closed, the medium does not exert pressure on the packing, facilitating maintenance. This is why stop valves cannot be installed in reverse. Other valves also have their own characteristics. The valve should be installed in a location that facilitates operation; even if installation is temporarily difficult, it is necessary to consider the operator’s long-term work needs. It is best for the valve handwheel to be at chest level (usually 1.2 meters above the operating floor), as this makes it easier to open and close the valve. The handwheel of the floor valve should face upward and not be tilted, to avoid awkward operation. For wall-mounted units, space must also be left near the device’s valves for the operator to stand. It is necessary to avoid working with substances that require looking up, especially acids, bases, toxic substances, etc., as it is very unsafe to do so. The gate valve must not be installed upside down (with the handwheel facing downward), as this will cause the medium to remain in the space above the valve cover for an extended period, leading to corrosion of the valve stem; it is also prohibited by certain process requirements. It is also very inconvenient to replace the packing at the same time. Straight-through gate valves should not be installed underground, as moisture can cause corrosion of the exposed valve stem. For lift-type check valves, it is necessary to ensure that their valve discs are vertical during installation, so as to allow for smooth lifting and lowering. For swing check valves, it is necessary to ensure that their pin shafts are horizontal during installation, so as to allow for smooth swinging. The pressure relief valve must be installed vertically on a horizontal pipe, without any tilt in any direction. (II) Care must be taken during the installation of valves; it is essential to avoid impacting valves made of brittle materials. Before installation, the valve should be inspected to verify its specifications and model, and to check for any damage, especially to the valve stem. It needs to be turned a few more times to check if it is skewed, as the valve stem is most likely to get damaged during transportation. The debris inside the valve also needs to be removed. When lifting the valve, do not tie the rope to the handwheel or valve stem, as this may damage those components; instead, it should be tied to the flange. The pipeline connected to the valve must be thoroughly cleaned. Compressed air can be used to blow away iron oxide filings, sediment, slag, and other debris. These debris not only easily scratch the sealing surfaces of the valves, but larger particles of debris (such as weld slag) can also block small valves, rendering them ineffective. When installing threaded valves, the sealing packing for power station valves (flax mixed with lead grease or PTFE tape) should be wrapped around the pipe threads, avoiding contact with the inside of the valve, so as to prevent accumulation there and disrupt the flow of the medium. When installing flanged valves, be careful to tighten the bolts symmetrically and evenly. The valve flange and the pipe flange must be parallel with an appropriate gap, to prevent excessive pressure from being generated on the valve, which could even lead to cracking. Special attention should be paid to brittle materials and valves with low strength. For valves that need to be welded to pipes, spot welding should be performed first, followed by fully opening the closing element, and then performing a full weld. (III) Valve protection facilities: Some valves also require external protection facilities, namely insulation and heat retention. Heating steam pipelines are sometimes also added inside the insulation layer. It depends on the production requirements to determine which types of valves should be insulated or kept cold. In principle, whenever the temperature of the medium inside the valve drops too much, it can affect production efficiency or damage the valve, in which case insulation – or even heating – is necessary; whenever the valve is exposed, as this is detrimental to production or can cause problems such as frosting, then cooling is required. Insulation materials include asbestos, slag wool, glass wool, perlite, diatomaceous earth, vermiculite, etc.; cooling materials include cork, perlite, foam, plastics, etc. Water and steam valves that have not been used for a long time must have any accumulated water drained. (IV) For some valves in bypass systems and instrumentation, in addition to the necessary protective devices, bypass systems and instrumentation are also required. A bypass has been installed to facilitate the maintenance of the steam trap. Other valves also have bypass installations. Whether to install a bypass depends on the condition of the valve, its importance, and the requirements of production. (5) Replace the packing in the valves; some of the packing is no longer functional, and some is not suitable for the medium being used, so it is necessary to replace the packing. Valve manufacturers cannot take into account the wide variety of different media used by end-users; ordinary packing is always installed in the stuffing box, but when in use, it is necessary to ensure that the packing is suitable for the medium in question. When replacing the packing, press it in circle by circle. The seams around each circle should be at a 45-degree angle, with the seams between circles offset by 180 degrees. The packing height must take into account the amount of additional compression that the gland can apply. At the same time, it is necessary to allow the lower part of the gland to compress the packing chamber to an appropriate depth; this depth is generally 10-20% of the total depth of the packing chamber. For high-demand valves, the seam angle is 30 degrees. The seams between the circles are offset by 120 degrees. In addition to the aforementioned packing materials, shaped packing materials such as rubber O-rings (natural rubber is resistant to weak alkalis at temperatures below 60 degrees Celsius, nitrile rubber is resistant to oils at temperatures below 80 degrees Celsius, and fluororubber is resistant to various corrosive agents at temperatures below 150 degrees Celsius), triple-layered polytetrafluoroethylene rings (resistant to highly corrosive agents at temperatures below 200 degrees Celsius), and nylon cup-shaped rings (resistant to ammonia and alkalis at temperatures below 120 degrees Celsius) can also be used depending on the specific circumstances. Wrapping a layer of PTFE tape around the ordinary asbestos packing can improve the sealing effect and reduce the electrochemical corrosion of the valve stem. When compressing the packing, turn the valve stem at the same time to ensure even compression around the perimeter and prevent it from being too tight; apply even force when tightening the gland, without tilting it.

The following points should be noted: 1. For non-metallic valves, some are hard and brittle while others have lower strength; therefore, when operating them, the force used for opening and closing should not be too great, and forceful actions should especially be avoided. Be careful to avoid objects bumping into each other as well. 2. When the weather is cold and the water valve remains closed for an extended period, any accumulated water behind the valve should be drained. After the steam valve stops supplying steam, the condensate also needs to be drained. There is a plug at the bottom of the valve, which can be opened to drain water. 3. When using a new valve, do not compress the packing too tightly – just enough to prevent leakage. This is to avoid excessive pressure on the valve stem, which could accelerate wear and make it difficult to open and close the valve. 4. For high-temperature valves operating at temperatures above 200°C, since they are installed at room temperature, the temperature rises during normal operation, causing the bolts to expand due to heat and increasing the gaps between them; therefore, it is necessary to tighten them again, a process known as \"thermal tightening\". Operators must pay attention to this step, as otherwise leaks can easily occur.