Avoid these 25 taboos in valve installation – instrument technicians can save time and effort

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Valves are the most common types of equipment in chemical plants. Installing valves may seem simple, but failing to follow the relevant technical procedures can lead to safety accidents. Today, Changhui Instruments would like to share with you some experience and knowledge regarding valve installation. Control valve yunrun.com.cn/product/list_88.html ◆Prohibition 1: Conducting hydrostatic tests at negative temperatures during winter construction. Consequence: The pipes were damaged by freezing due to rapid ice formation inside them during the hydrostatic test. Measure: Try to conduct the hydrostatic test before winter construction, and after the testing, blow out all the water; in particular, the water inside the valves must be completely removed, otherwise the valves may rust in mild cases or crack due to freezing in severe cases. When conducting hydrostatic tests on the project during winter, it is necessary to maintain a positive indoor temperature, and the water must be completely drained after the testing is completed. ◆Taboo 2: Inadequate flushing prior to the completion of the piping system; flow rate and velocity fail to meet the requirements for pipe flushing. It even uses drainage from a hydraulic pressure strength test to replace flushing. Consequences: The water quality fails to meet the requirements for the operation of the pipeline system, and this often leads to a reduction in the pipe’s cross-sectional area or even blockages. Measure: Flush using the maximum design flow rate within the system, or a water flow velocity of not less than 3 m/s. It is considered qualified if the color and transparency of the water at the outlet are visually consistent with those of the water at the inlet. ◆Prohibition 3: Sewage, rainwater, and condensate pipes shall not be covered up without undergoing a water-tightness test. Consequences: It may cause leaks and result in losses for the user. Measure: The water tightness test should be strictly inspected and accepted in accordance with the specifications. Plumbed sewage, rainwater, condensate pipes, etc., that are installed concealed underground, within ceilings, or between pipes must be made leak-free. ◆Taboo 4: During the hydraulic strength test and tightness test of piping systems, only the pressure values and water level changes are observed; insufficient attention is paid to detecting leaks. Consequence: Leaks occur in the piping system after it starts operating, affecting normal use. Measures: When testing the piping system in accordance with design requirements and construction specifications, apart from recording any changes in pressure or water level within the specified time frame, it is essential to carefully check for any signs of leakage. ◆Prohibition 5: Do not use ordinary valve flanges for butterfly valve flanges. Consequences: The dimensions of butterfly valve flanges and those of ordinary valve flanges are different. In some cases, the inner diameter of the flange is smaller than the size of the butterfly valve’s disc, resulting in the valve being unable to open or causing damage to the valve when forced open. Measure: The flange should be manufactured according to the actual dimensions of the butterfly valve flange. ◆Taboo 6: No holes or embedded parts are provided during the construction of the building structure; or the size of the reserved holes is too small, and the embedded parts are not marked. Consequences: During the construction of heating and ventilation systems, the building structure is damaged, and in some cases the load-bearing rebar is severed, which affects the safety of the building. Measures: Thoroughly study the construction drawings for heating and plumbing projects, and in accordance with the requirements for installing pipes as well as supports and hangers, proactively and carefully cooperate with the construction of openings and embedded components in the building structure, following the design specifications and construction standards. ◆Prohibition 7: When welding pipes, if the ends of the pipes are not aligned on the same center line after alignment, there is no gap between them; thick-walled pipes are not prepared with bevels, and the width and height of the weld do not meet the requirements specified in the construction standards. Consequences: The misalignment of pipes, where they are not on the same centerline, directly affects both the welding quality and the visual appearance. There are no gaps at the joints; thick-walled pipes do not require beveling. If the width and height of the welds do not meet the specified requirements, the welds will not have the necessary strength. Measure: After aligning the pipes for welding, they must not be misaligned; they should be on the same center line ； A gap should be left for alignment ； Thick-walled pipes require beveling. Additionally, the width and height of the welds should be welded in accordance with the specification requirements. ◆Prohibition 8: Pipes are directly buried in frozen soil and untreated loose soil; the spacing and placement of pipe supports are improper; in some cases, bricks are simply laid dry without any treatment. Consequence: The pipeline was damaged during the compaction of the backfill due to unstable support, resulting in rework and repairs. Measures: Pipes must not be buried in permafrost or untreated loose soil. The spacing between supports must comply with the requirements of construction standards, and the supports must be secure, especially at the pipe joints, which should not be subjected to shear forces. Brick piers should be constructed with cement mortar to ensure they are complete and sturdy. ◆Taboo 9: The expansion bolts used to secure pipe supports are of poor quality; the holes drilled for these bolts are too large; or the expansion bolts are installed in brick walls or even lightweight walls. Consequences: The pipe supports become loose, the pipes deform, and may even fall off. Measures: Only qualified expansion bolts must be selected; sampling and testing should be conducted when necessary. The diameter of the hole for installing an expansion bolt must not exceed the bolt’s outer diameter by more than 2 mm. Expansion bolts should be used on concrete structures. ◆Prohibition 10: The flanges and gaskets used for pipe connections are not strong enough, and the connection bolts are short or have a small diameter. Rubber gaskets are used for hot water pipes, while double-layer or beveled gaskets are employed for cold water pipes; the flange gasket extends into the pipe. Consequence: The flange connection is not tight, or may even be damaged, resulting in leaks. Flange gaskets protruding into the pipe increase water flow resistance. Measure: The flanges and gaskets used for pipes must meet the requirements of the design working pressure of the pipes. Rubber-asbestos gaskets are recommended for the flange gaskets of heating and hot water supply pipes ； Rubber gaskets are recommended for the flange gaskets of water supply and drainage pipes. The gasket of the flange must not protrude into the pipe; its outer edge should be at the level of the flange bolt holes. No beveled shims or multiple gaskets shall be placed in the middle of the flange. The diameter of the bolts used to connect the flanges should be at least 2 mm smaller than the diameter of the flange holes, and the length of the bolt shaft protruding from the nut should be half the thickness of the nut. ◆Prohibition 11: Incorrect valve installation method. For example, in the case of globe valves or check valves, if the flow direction of water (steam) is opposite to that indicated by the markings, the valve stem should be installed downward; horizontally mounted check valves should be installed vertically. Gate valves or butterfly valves with exposed stems do not have any space for opening or closing, while the stem of valves with concealed stems is not oriented toward the inspection door. Consequences: Valve malfunction, difficulty in maintaining or repairing the valve; when the valve stem points downward, it often leads to leaks. Measures: Install the valves strictly in accordance with the installation instructions. For gate valves with visible stems, ensure sufficient clearance for the stem to extend during operation; for butterfly valves, take into account enough space for the handle to rotate. The stems of all types of valves must not be below the horizontal position, let alone point downward. For concealed valves, not only must inspection doors be provided to meet the requirements for opening and closing the valves, but the valve stem should also face toward those inspection doors. ◆Taboo 12: The specifications and model of the installed valve do not meet the design requirements. For example, the nominal pressure of the valve is lower than the system test pressure ； For water supply branch pipes with a diameter less than or equal to 50 mm, gate valves shall be used ； Gate valves are used for the dry and vertical pipes in hot water heating systems ； Butterfly valves are used for the suction pipes of fire pump systems. Consequences: It affects the normal opening and closing of the valve, as well as functions such as resistance and pressure regulation. It even caused the valves to get damaged during system operation, forcing repairs. Measure: Be familiar with the application ranges of various types of valves, and select the appropriate specifications and models of valves in accordance with the design requirements. The nominal pressure of the valve must meet the requirements of the system’s test pressure. According to the construction specifications: globe valves shall be used for water supply branch pipes with a diameter of 50 mm or less ； Gate valves should be used when the pipe diameter is greater than 50 mm. Gate valves should be used for the dry and vertical control valves in hot water heating systems, and butterfly valves should not be used for the suction pipes of fire pumps. ◆Prohibition 13: Failing to conduct the necessary quality inspections as required before installing the valves. Consequences: During system operation, the valves fail to operate smoothly, do not close properly, and leakage of water (steam) occurs, leading to rework and repairs, and even affecting normal water (steam) supply. Measure: Before installing the valve, pressure resistance and tightness tests should be conducted. For testing, 10% of the items in each batch (of the same grade, specifications, and model) shall be sampled, with a minimum of one sample. For the shut-off valves installed on the main pipes, strength and tightness tests shall be conducted on each one individually. The test pressures for valve strength and tightness shall comply with the provisions of the “Code for Acceptance of Construction Quality of Building Water Supply, Drainage and Heating Engineering” (GB 50242-2002). ◆Prohibition 14: The main materials, equipment, and products used in construction lack technical quality assessment documents or product certification certificates that comply with ** or the current industry standards. Consequences: The project quality is unsatisfactory, there are potential accident risks, it cannot be delivered for use on schedule, and remedial work must be carried out ； This results in project delays and increased labor and material costs. Measure: The main materials, equipment, and products used in water supply, drainage, heating, and ventilation projects shall be accompanied by technical quality certification documents or product certificates that meet ** or the current standards issued by relevant departments ； It should indicate the product name, model, specifications, **quality standard code, date of manufacture, name and location of the manufacturer, as well as the certificate or code verifying the quality of the product. ◆Prohibition 15: Installing valves in the wrong orientation. Consequence: Valves such as stop valves, throttle valves, pressure relief valves, and check valves all have a directional requirement; if installed incorrectly, throttle valves will affect their performance and lifespan ； The pressure relief valve doesn’t work at all, and the check valve can even be dangerous. Measure: For ordinary valves, there are direction indicators on the valve body ； In the event that it is not present, it should be correctly identified based on the working principle of the valve. The valve chamber of the globe valve is asymmetrical on the left and right sides. The fluid must flow from bottom to top through the valve opening; this results in low fluid resistance (determined by its shape), easy operation when opening (due to the upward direction of the medium pressure), and no pressure exerted on the packing after closure, thereby facilitating maintenance. This is why a stop valve must not be installed backwards. The gate valve should 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-stem 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. ◆Prohibition 16: Operating manual valves with excessive force. Consequences: In mild cases, the valve may be damaged; in severe cases, it can lead to safety accidents. Measures: The handwheel or handle of a manual valve is designed to accommodate normal human strength, taking into account the strength of the sealing surface and the necessary force required for closing it. Therefore, it cannot be moved 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 and closing the valve, the force applied should be steady; no sudden impacts are allowed. 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 opened, the handwheel should be turned back slightly to ensure a tight fit between the threads, 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 wash 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 adhere to 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 they are closed, the closing element expands due to heat, making it difficult to open them. If it is necessary to open them at this time, the valve cover threads can be loosened by half a turn to one full turn to relieve stress on the valve stem, after which the handwheel can be turned. ◆Prohibition 17: Improper installation of valves in high-temperature environments. Consequence: Leakage accidents. Measure: For valves operating at temperatures above 200°C, since they are installed at normal temperatures and the temperature rises during normal use, causing the bolts to expand due to heat and the gaps to increase, it is necessary to tighten them again; this process is known as “thermal tightening”. Operators must pay attention to this step, otherwise leakage is likely to occur. ◆Prohibition 18: Failing to drain water in cold weather. Measure: When the weather is cold and the water valves remain closed for extended periods, the water accumulated behind the valves should be drained. After the steam valve stops supplying steam, the condensate must also be drained. There is a plug at the bottom of the valve, which can be opened to drain water. ◆Prohibition 19: Non-metallic valves with excessive opening and closing force. Solution: Some non-metallic valves are hard and brittle, while others have low strength; therefore, the force used for opening and closing them should not be too great, and forceful actions should especially be avoided. Be careful to prevent the object from being bumped. ◆Prohibition 20: Over-tightening the packing of new valves. Solution: When using new valves, do not tighten the packing too much; just enough to prevent leakage. This avoids excessive stress 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 its performance; therefore, careful attention must be paid to the direction and position of the valves, as well as to the valve installation procedures, protective devices for the valves, bypass systems and instruments, and the replacement of valve packing. ◆Prohibition 21: No operating space at the installation location. Measure: The valve must be installed in a location that facilitates operation; even if installation is temporarily difficult, consideration should be given to 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. ◆Prohibition 22: Impacting valves made of brittle materials. Measure: Care must be taken during installation to avoid impacting valves constructed from 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 pipelines 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 large particles of debris (such as welding slag) can also block small valves, rendering them ineffective. When installing threaded valves, the sealing filler (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. ◆Prohibition 23: Valves lack insulation and cooling measures. Solution: Some valves also require external protective devices, namely insulation and cooling. 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 insulated from heat. In principle, whenever the temperature of the medium inside the valve drops too much, it can affect production efficiency or damage the valve; in such cases, insulation is necessary, and sometimes even heat tracing ； When valves are exposed, which is detrimental to production or can cause problems such as frosting, insulation is required. Insulation materials include asbestos, slag wool, glass wool, perlite, diatomaceous earth, vermiculite, etc.; cooling materials include cork, perlite, foam, plastic, etc. ◆Prohibition 24: No bypass installed for the steam trap. Action: Some valves require not only necessary protective devices but also bypasses and instruments. A bypass has been installed to facilitate the maintenance of the steam trap. Other valves also have bypasses for installation. Whether to install a bypass depends on the condition of the valve, its importance, and the requirements of production. ◆Prohibition 25: Failure to replace the packing regularly. Action: Keep valves in stock; 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. Facing a wide variety of different media, ordinary packing is always used in the stuffing box of valves; however, when in use, it is necessary to ensure that the packing is suitable for the specific medium. When replacing the packing, press it in circle by circle. The seams around each loop should be at a 45-degree angle, with the seams between loops 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 valves with high requirements, the seam angle is 30 degrees. The joints 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.