Twenty-five taboos for valve installation

Valves are the most common equipment in chemical companies. Installing valves seems easy, but if they are not carried out by relevant technologies, safety accidents will occur. Today, I will share with you some experience and knowledge about valve installation.


1. Taboo: Conducting water pressure test at negative temperature during winter construction.
Consequences: The pipe freezes quickly during the water pressure test, causing the pipe to freeze.
Measures: Try to conduct a water pressure test before winter construction, and blow the water clean after the pressure test, especially the water in the valve must be cleared, otherwise the valve will rust or freeze.
When the project must conduct a water pressure test in winter, it must be carried out at a positive indoor temperature, and the water must be blown clean after the pressure test.


2. Taboo: The flushing of the steel pipeline system before completion is not serious, and the flow rate and speed do not meet the flushing requirements of the steel pipeline. Even the water pressure strength test is used to drain water instead of flushing.
Consequences: The water quality does not meet the operation requirements of the steel pipeline system, and often causes the cross-section of the steel pipeline to be reduced or blocked.
Measures: Flush with the system's set juice flow or a water flow rate that should not be less than 3m/s. The color and transparency of the water at the outlet should be consistent with the color and transparency of the water at the inlet.


3. Taboo: Concealing sewage, rainwater, and condensate pipes without a water-tightness test.
Consequences: It may cause leakage and cause losses to users.
Measures: The water-tightness test should be strictly inspected and accepted according to the specifications. Concealed sewage, rainwater, and condensate pipes buried underground, in suspended ceilings, and between steel pipes must be ensured to be leak-proof.


4. Taboo: During the water pressure strength test and tightness test of the steel pipeline system, only the pressure value and water level changes are observed, and the leakage inspection is not enough.
Consequences: Leakage occurs after the steel pipeline system is put into operation, affecting normal use.
Measures: When the steel pipeline system is tested according to the design requirements and construction specifications, in addition to recording the pressure value or water level changes within the specified time, it is particularly important to carefully check whether there is a leakage problem.


5. Taboo: Use ordinary valve flanges for butterfly valve flanges.
Consequences: The size of the butterfly valve flange is different from that of the ordinary valve flange. Some flanges have a small inner diameter, while the butterfly valve has a large disc, which causes the valve to be unable to open or to be opened rigidly, causing damage to the valve.
Measures: The flange should be processed according to the actual size of the butterfly valve flange.


6. Taboos: There are no reserved holes and embedded parts in the construction of the building structure, or the reserved holes are too small and the embedded parts are not marked.
Consequences: During the construction of the heating and sanitary project, the building structure is chiseled and even the stressed steel bars are cut, affecting the safety performance of the building.
Measures: Carefully familiarize yourself with the construction drawings of the heating and sanitary project, and actively and conscientiously cooperate with the construction of the building structure to reserve holes and embedded parts according to the needs of the installation of steel pipes and supports and hangers, and refer to the design requirements and construction specifications for specific details.


7. Taboos: When welding steel pipes, the steel pipe staggered mouth is not on a center line after the joint, no gap is left for the joint, the thick-walled pipe is not beveled, and the width and height of the weld do not meet the requirements of the construction specifications.
Consequences: The steel pipe staggered mouth is not on a center line, which directly affects the welding quality and visual quality. There is no gap between the joints, the thick-walled pipes are not beveled, the width and height of the weld do not meet the requirements, and the welding cannot meet the strength requirements.
Measures: After welding the steel pipes, the steel pipes cannot be misaligned and must be on the same center line; gaps should be left between the joints; thick-walled pipes must beveled. In addition, the width and height of the welds should be welded by the specifications.


8. Taboo: Steel pipes are directly buried on frozen soil and untreated loose soil, the spacing and position of steel pipe piers are inappropriate, and even dry bricks are used.
Consequences: Due to unstable support, the steel pipes are damaged during the backfilling and tamping process, resulting in rework and repair.
Measures: Steel pipes must not be buried on frozen soil and untreated loose soil. The spacing of piers must meet the requirements of construction specifications, and the pads must be firm, especially at the steel pipe interfaces, which should not be subjected to shear force. Brick piers should be built with cement mortar to ensure integrity and firmness.


9. Taboo: The expansion bolts used to fix the steel pipe bracket are made of inferior materials, the hole diameter of the expansion bolts is too large, or the expansion bolts are installed on brick walls or even lightweight walls.
Consequences: The steel pipe bracket is loose, the steel pipe is deformed, or even falls off.
Measures: Qualified expansion bolts must be selected, and sampling should be carried out for testing and inspection when necessary. The hole diameter of the expansion bolt should not be larger than the outer diameter of the expansion bolt by 2mm, and the expansion bolt should be used on concrete structures.


10. Taboo: The flange and gaskets connected to the steel pipe are not strong enough, and the connecting bolts are short or thin in diameter. Rubber pads are used for thermal steel pipes, double-layer pads or bevel pads are used for cold water steel pipes, and flange gaskets protrude into the pipe.
Consequences: The flange connection is not tight, or even damaged, and leakage occurs. Flange gaskets protruding into the pipe will increase water flow resistance.
Measures: Flanges and gaskets for steel pipes must meet the requirements of the design working pressure of steel pipes.
Flange gaskets for heating and hot water supply steel pipes should use rubber asbestos pads; flange gaskets for water supply and drainage steel pipes should use rubber pads.
The gasket of the flange shall not protrude into the pipe, and its outer circle shall be as close to the flange bolt hole as possible. Bevel gaskets or several gaskets shall not be placed in the middle of the flange. The bolt diameter of the flange connection should be less than 2mm than the flange hole diameter, and the length of the bolt rod protruding from the nut should be 1/2 of the nut thickness.


11. Taboo: Wrong valve installation method.
For example, the water (steam) flow direction of the stop valve or check valve is opposite to the mark, the valve stem is installed downward, the horizontally installed check valve is installed vertically, the handle of the rising stem gate valve or butterfly valve has no opening and closing space, and the valve stem of the concealed valve does not face the inspection door.
Consequences: Valve failure, difficult opening and closing maintenance, and the valve stem facing downward often cause water leakage.
Measures: Install strictly according to the valve installation instructions, the rising stem gate valve leaves enough valve stem extension opening height, the butterfly valve fully considers the handle rotation space, and the various valve stems cannot be lower than the horizontal position, let alone downward. Concealed valves should not only be equipped with inspection doors that meet the needs of valve opening and closing, but also the valve stem should face the inspection door.


12. Taboo: The specifications and models of the installed valves do not meet the design requirements.
For example, the nominal pressure of the valve is less than the system test pressure; the gate valve is used when the diameter of the water supply branch pipe is less than or equal to 50mm; the stop valve is used for the dry and vertical pipes of hot water heating; the butterfly valve is used for the suction pipe of the fire pump.
Consequences: Affect the normal opening and closing of the valve and the adjustment of resistance, pressure, and other functions. Even cause the valve to be damaged and forced to repair during system operation.
Measures: Be familiar with the application range of various valves and select the specifications and models of the valves according to the design requirements. The nominal pressure of the valve must meet the requirements of the system test pressure. According to the construction specifications: the stop valve should be used when the diameter of the water supply branch pipe is less than or equal to 50mm; when the diameter is greater than 50mm, the gate valve should be used. The gate valve should be used for the dry and vertical control valves of hot water heating, and the butterfly valve should not be used for the suction pipe of the fire pump.


13. Taboo: Failure to carry out necessary quality inspections before installing the valves as required.
Consequences: The valves are not flexible during system operation, are not tightly closed, and leak (steam) occurs, resulting in rework and repair, and even affecting normal water (steam) supply.
Measures: Before installing the valve, a pressure resistance strength and tightness test should be performed. The test should be conducted by sampling 10% of each batch (same brand, same specification, same model), and no less than one.
For closed-circuit valves installed on the main pipe to cut off, strength and tightness tests should be performed one by one. The valve strength and tightness test pressure should comply with the "Construction Quality Acceptance Code for Building Water Supply, Drainage and Heating Engineering" (GB50242-2002).


14. Taboos: The main materials, equipment, and products used in the construction lack technical quality appraisal documents or product certificates that meet the current national or ministerial standards.
Consequences: The project quality is unqualified, there are potential safety hazards, it cannot be delivered on time, and rework and repair are required; resulting in delays in the construction period and increased labor and material inputs.
Measures: The main materials, equipment, and products used in water supply and drainage and heating and sanitary engineering should have technical quality appraisal documents or product certificates that meet the current standards issued by the state or the ministry; the product name, model, specification, national quality standard code, factory date, manufacturer name and location, factory product inspection certificate or code should be indicated.


15. Taboo: Inverted valve installation
Consequences: Valves such as stop valves, throttle valves, pressure-reducing valves, and check valves are directional. If they are installed upside down, the throttle valve will affect the use effect and life; the pressure-reducing valve will not work at all, and the check valve may even cause danger.
Measures: Generally, valves have directional marks on the valve body; if there are no directional marks, they should be correctly identified according to the working principle of the valve. The valve cavity of the stop valve is asymmetrical on the left and right, and the fluid should be allowed to pass through the valve port from bottom to top so that the fluid resistance is small (determined by the shape), the opening is labor-saving (because the medium pressure is upward), and the medium does not press the packing after closing, which is convenient for maintenance. This is why the stop valve cannot be installed in reverse.
Do not install the gate valve upside down (i.e. the hand wheel is facing downward), otherwise, the medium will remain in the valve cover space for a long time, which is easy to corrodes the valve stem and is taboo for some process requirements. At the same time, it is extremely inconvenient to replace the packing.
Do not install the rising stem gate valve underground, otherwise the exposed valve stem will be corroded due to moisture.
When installing the lifting check valve, ensure that its valve disc is vertical so that it can be lifted and lowered flexibly.
When installing the swing check valve, ensure that its pin shaft is horizontal so that it can swing flexibly.
The pressure-reducing valve should be installed upright on the horizontal steel pipeline without tilting in any direction.


16. Taboo: Opening and closing manual valves with excessive force
Consequences: Damage to the valve at the least, or safety accidents at the worst
Measures: The handwheel or handle of the manual valve is designed according to ordinary manpower, taking into account the strength of the sealing surface and the necessary closing force. Therefore, it cannot be moved with a long lever or a long wrench. Some people are accustomed to using wrenches and should be strictly careful not to use too much force, otherwise, it is easy to damage the sealing surface or break the handwheel or handle. When opening and closing the valve, the force should be stable and not impact. Some components of high-pressure valves that are opened and closed by impact have taken into account that this impact force is not equal to that of general valves. For steam valves, they should be pre-heated and condensed water should be removed before opening. When opening, they should be opened as slowly as possible to avoid water hammer. When the valve is fully opened, the handwheel should be reversed a little to tighten the threads to avoid loosening and damage. For rising stem valves, remember the valve stem position when fully opened and fully closed to avoid hitting the top dead center when fully opened. It is also convenient to check whether it is normal when fully closed. If the valve handle falls off, or large debris is embedded between the valve core seal, the valve stem position when fully closed will change. When the pipeline is first used, there is a lot of dirt inside. The valve can be slightly opened, and the high-speed flow of the medium can be used to flush it away, and then it can be gently closed (not closed quickly or violently to prevent residual impurities from pinching the sealing surface), and then opened again. Repeat this process many times to flush the dirt and put it into normal operation. For normally open valves, there may be dirt on the sealing surface. When closing, it should also be flushed clean with the above method, and then formally closed. If the handwheel or handle is damaged or lost, it should be replaced immediately. It should not be replaced with a loose plate to avoid damaging the valve stem and opening and closing, which may cause accidents in production. Some media cool down after the valve is closed, causing the valve parts to shrink. The operator should close it again at an appropriate time to leave no cracks on the sealing surface. Otherwise, the medium will flow through the cracks at high speed and easily erode the sealing surface. During the operation, if it is found that the operation is too strenuous, the cause should be analyzed. If the packing is too tight, it can be loosened appropriately. If the valve stem is skewed, the personnel should be notified to repair it. For some valves, when they are closed, the closing parts expand due to heat, making it difficult to open. If you must open them at this time, you can loosen the valve cover thread by half a turn to one turn to eliminate the valve stem stress, and then turn the handwheel.


17. Taboo: Improper installation of valves in high-temperature environments
Consequences: Leakage accidents
Measures: High-temperature valves above 200℃ are at room temperature during installation, and after normal use, the temperature rises, the bolts expand due to heat, and the gap increases, so they must be tightened again, which is called "hot tightening". Operators should pay attention to this work, otherwise leakage is likely to occur.


18. Taboo: Failure to drain water in cold weather
Measures: When the weather is cold, the water valve is closed for a long time, and the water behind the valve should be drained. After the steam valve stops steam, the condensate should also be drained. If there is a wire plug at the bottom of the valve, it can be opened to drain water.


19. Taboo: Non-metallic valves, too much opening and closing force
Measures: Some non-metallic valves are hard and brittle, and some have low strength. When operating, the opening and closing force should not be too large, especially not violent. Also, pay attention to avoid collisions with objects.


20. Taboo: The packing of new valves is pressed too tightly
Measures: When using new valves, the packing should not be pressed too tightly, so as not to leak, to avoid excessive pressure on the valve stem, accelerated wear, and difficulty in opening and closing. The quality of valve installation directly affects the use, so you must pay attention to the direction and position of the valve, valve construction, valve protection facilities, bypass and instrumentation, and valve packing replacement.


21. Taboo: No operating space at the installation location
Measures: The location where the valve is installed must be convenient for operation; even if the installation is temporarily difficult, it is also necessary to consider the long-term work of the operator. The valve handwheel is aligned with the chest (generally 1.2 meters away from the operating floor) so that it is easier to open and close the valve. The handwheel of the floor-standing valve should be facing up and not tilted to avoid awkward operation. For valves against the wall or equipment, there should also be room for the operator to stand. Avoid looking up at the sky, especially for acid, alkali, toxic media, etc., otherwise it is very unsafe.


22. Taboo: Hitting valves made of brittle materials
Measures: The installation and construction must be careful, and valves made of brittle materials must not be hit. Before installation, the valve should be inspected, the specifications and models should be checked, and any damage should be identified, especially for the valve stem. It should also be turned a few times to see if it is skewed because the valve stem is most likely to be skewed during transportation. It is also necessary to remove debris from the valve. When lifting the valve, the rope should not be tied to the handwheel or valve stem to avoid damaging these parts, but should be tied to the flange. The pipeline connected to the valve must be cleaned. Compressed air can be used to blow away iron oxide filings, mud, welding slag, and other debris. This debris not only easily scratches the sealing surface of the valve, but also large particles of debris (such as welding slag) can block small valves and make them ineffective. When installing a screw-mouth valve, the sealing packing (hemp plus lead oil or polytetrafluoroethylene raw tape) should be wrapped on the steel pipe thread, and should not be put into the valve to avoid accumulation in the valve and affect the flow of the medium. When installing a flange valve, pay attention to tightening the bolts symmetrically and evenly. The valve flange and the steel pipe flange must be parallel, with a reasonable gap to avoid excessive pressure on the valve or even cracking. For valves made of brittle materials and low strength, special attention should be paid. Valves that need to be welded to steel pipes should be spot welded first, then the closing parts should be fully opened and then welded shut.


23. Taboo: The valve is not insulated and cooled
Measures: Some valves must also have external protection facilities, which are insulation and cooling. Sometimes, a heating steam pipeline is added to the insulation layer. What kind of valve should be insulated or cooled depends on production requirements. In principle, if the temperature of the medium in the valve is reduced too much, it will affect production efficiency or freeze the valve, and it needs to be insulated or even heated; if the valve is exposed, it is not conducive to production or causes adverse phenomena such as frost, it needs to be cooled. Insulation materials include asbestos, slag wool, glass wool, perlite, diatomaceous earth, vermiculite, etc.; cooling materials include cork, perlite, foam, plastic, etc.


24. Taboo: The steam trap is not installed with a bypass
Measures: In addition to the necessary protection facilities, some valves also need bypasses and instruments. Bypasses are installed to facilitate steam trap maintenance. Other valves also have bypasses installed. Whether to install a bypass depends on the valve condition, importance, and production requirements.


25. Taboo: Failure to replace packing regularly
Measures: For stock valves, some packings are no longer useful, and some are not compatible with the medium used, which requires the packing to be replaced.
The valve faces thousands of different media, and the stuffing box is always filled with ordinary packing, but when used, the packing must be adapted to the medium.
When replacing the packing, press it in one circle at a time. Each circle joint is preferably 45 degrees, and the circle joints are staggered 180 degrees. The packing height should take into account the room for the gland to continue to tighten, and now the gland should be allowed to press the packing chamber to an appropriate depth, which can generally be 10-20% of the total depth of the packing chamber.
For valves with high requirements, the joint angle is 30 degrees. The joints between circles are staggered 120 degrees.


In addition to the above-mentioned packings, rubber O-rings (natural rubber is resistant to weak alkali below 60 degrees Celsius, nitrile rubber is resistant to oil below 80 degrees Celsius, and fluoro rubber is resistant to various corrosive media below 150 degrees Celsius), three-piece stacked polytetrafluoroethylene rings (resistant to strong corrosive media below 200 degrees Celsius), and nylon bowl rings (resistant to ammonia and alkali below 120 degrees Celsius) can also be used according to specific conditions. Wrapping a layer of polytetrafluoroethylene raw tape outside 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 keep it even all around and prevent it from being too tight. Tighten the gland evenly and do not tilt it.