A valve is a device used to control the direction, pressure, and flow of fluid in a fluid system. During the construction process, the quality of valve installation directly affects the normal operation in the future, so attention must be paid. How did the three-barrel oil workers install the valves? What are the main points, taboos and precautions for valve installation?
5 main points
Direction and location
Many valves are directional
For example, stop valve, throttle valve, pressure reducing valve, check valve, etc., if installed upside down, it will affect the use effect and life (such as throttle valve), or it will not work at all (such as pressure reducing valve), or even Cause danger (such as check valve). Normal valves have direction signs on the valve body. If not, it should be correctly identified according to the valve working principle.
The valve cavity of the shut-off valve is asymmetrical, and the fluid should pass through the valve port from bottom to top, so that the fluid resistance is small (determined by the shape), and 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 the reason why the globe valve can not be reversed. Other valves also have their own characteristics.
The valve installation position must be easy to operate
Even if the installation is temporarily difficult, it is necessary to consider the long-term work of the operator. It is best to keep the valve handwheel flush with the chest (usually 1.2 meters away from the operating floor), so that it is easier to open and close the valve. The hand wheel of the floor valve should be upwards, do not tilt, so as to avoid awkward operation. The valve of the wall machine and the equipment should also leave room for the operator to stand. It is necessary to avoid operating from the sky, especially acid and alkali, toxic media, etc., otherwise it is very unsafe.
Do not install the gate upside down (that is, the handwheel is down), otherwise the medium will remain in the valve cover space for a long time, which will easily corrode the valve stem, and it is contraindicated by certain process requirements. At the same time, it is extremely inconvenient to replace the packing. The exposed stem gate valve should not be installed underground, otherwise the exposed stem will be corroded due to moisture. When installing the lift check valve, make sure that its valve flap is vertical, so that it can be lifted and moved flexibly. For swing check valves, ensure that their pin shafts are level when installing, so that they can swing flexibly. The pressure reducing valve should be installed upright on a horizontal pipe, and should not be tilted in all directions.
The installation and construction must be careful, and never hit the valve made of brittle materials.
It is necessary to carefully check whether the models and specifications of all valves meet the design requirements.
(According to the valve model and factory instructions, check whether they can be used under the required conditions, and if necessary, make a water pressure or air pressure test.)
In addition, check whether the packing is intact, whether the gland bolts have sufficient adjustment margin, and whether the valve stem and valve disc are smart, whether they are stuck or skewed.
(The sealing surface of the valve disc must be closed tightly. For threaded valves, the thread quality should be checked. Unqualified valves cannot be installed and should be stacked or marked separately.)
Clear the debris in the valve.
When the valve is hoisted, the rope should not be tied to the handwheel or valve stem to avoid damaging these parts. It 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 sand, welding slag and other debris. These debris are not only easy to scratch the sealing surface of the valve, the large particles of debris (such as welding slag) can also block the small valve and make it invalid.
When installing the screw valve, the sealing packing (wire hemp plus aluminum oil or PTFE tape) should be wrapped on the pipe thread, and do not get into the valve, so as to avoid the accumulation of the valve and affect the flow of the medium.
When installing the flange valve, pay attention to tighten the bolts symmetrically and evenly. The valve flange and pipe flange must be parallel with reasonable clearance to avoid excessive pressure or even cracking of the valve. Special attention should be paid to valves with brittle materials and low strength. Valves that need to be welded to the pipe should be spot welded first, then the closing part should be fully opened, and then welded to death.
Some valves also need external protection, which is heat preservation and cold preservation. Hot steam pipelines are sometimes added in the insulation layer. What kind of valve should be kept warm or cold depends on the production requirements.
In principle, if the medium in the valve reduces the temperature too much, it will affect the production efficiency or freeze the valve, it needs to be kept warm, or even mixed with heat; where the valve is exposed, which is unfavorable to production or causes frost and other undesirable phenomena, it needs to be kept cold. Thermal insulation materials include asbestos, slag wool, glass wool, perlite, diatomaceous earth, vermiculite, etc.; cold insulation materials include cork, perlite, foam, plastics, etc.
Bypass and meter
In addition to the necessary protection facilities, some valves also have bypasses and meters. A bypass is installed. Facilitate the maintenance of the trap. For other valves, bypasses are also installed. Whether to install the bypass depends on the valve condition, importance and production requirements.
In stock valves, some packing is not good enough, and some are not in line with the used medium, which requires replacement of packing.
Valve manufacturers cannot consider the use of various types of different media. The stuffing box is always filled with ordinary packing, but when using it, the packing must be compatible with the medium.
When replacing the packing, press it in circle by circle. The seam of each circle should be 45 degrees, and the circle and circle should be opened by 180 degrees. The height of the packing should consider the room for the gland to continue to be compacted. At present, the packing chamber at the lower part of the gland should be at an appropriate depth. This depth can generally be 10-20% of the total depth of the packing chamber. For demanding valves, the seam angle is 30 degrees. The seams between the circles are staggered by 120 degrees.
In addition to the above fillers, three rubber O-rings (natural rubber resistant to weak alkalis below 60 degrees Celsius, nitrile rubber resistant to oil crystals below 80 degrees Celsius, and fluoro rubber resistant to various corrosive media below 150 degrees Celsius) can be used according to specific conditions. Stacked polytetrafluoroethylene ring (resistant to strong corrosive media below 200 degrees Celsius) and nylon bowl-shaped ring (resistant to ammonia and alkali below 120 degrees Celsius) and other forming fillers. Outside the ordinary asbestos packing, a layer of PTFE raw material tape can improve the sealing effect and reduce the electrochemical corrosion of the valve stem. When pressing the seasoning, turn the valve stem at the same time to keep the surrounding uniform and prevent it from being too dead. Tighten the gland with even force and not tilt.
14 big taboos
The main materials, equipment and products used in construction lack technical quality appraisal documents or product qualification certificates that meet the current national or ministerial standards.
as a result of
The quality of the project is unqualified, there are hidden dangers of accidents, it cannot be delivered on time, and must be reworked and repaired; it causes delays in the construction period and increases the input of labor and materials.
The main materials, equipment and products used in water supply and drainage and heating and sanitation projects should have technical quality appraisal documents or product qualification certificates that meet the current standards issued by the state or ministry; their product names, models, specifications, national quality standard codes, Factory date, manufacturer’s name and location, factory product inspection certificate or code number.
The necessary quality inspection is not carried out in accordance with the regulations before the valve is installed.
as a result of
In the operation of the system, the valve opening and closing is not flexible, the closing is not tight and the water leakage (steam) phenomenon occurs, which causes rework and repair, and even affects the normal water supply (steam).
Before the valve is installed, the pressure strength and tightness test should be done. In the test, 10% of the quantity of each batch (same brand, same specification, and same model) shall be randomly checked, and no less than one. For closed-circuit valves installed on the main pipe to cut off, the strength and tightness tests should be done one by one. The valve strength and tightness test pressure should meet the requirements of “Code for Construction Quality Acceptance of Building Water Supply and Drainage and Heating Engineering” (GB 50242-2002).
The specifications and models of the installed valve do not meet the design requirements. For example, the nominal pressure of the valve is less than the system test pressure; the water supply branch pipe adopts a gate valve when the pipe diameter is less than or equal to 50mm; the dry and stand pipe of the hot water heating adopts a stop valve; the fire water pump suction pipe adopts a butterfly valve.
as a result of
Affect the normal opening and closing of the valve and adjust the resistance, pressure and other functions. Even during the operation of the system, the valve is damaged and forced to be repaired.
Familiar with the application range of various valves, select valve specifications and models according to design requirements. The nominal pressure of the valve must meet the requirements of the system test pressure. According to the requirements of the construction specification: the water supply branch pipe diameter is less than or equal to 50mm should use a stop valve; when the pipe diameter is greater than 50mm, a gate valve should be used. Gate valves should be used for hot water heating dry and vertical control valves, and butterfly valves should not be used for the suction pipe of fire water pumps.
The valve installation method is wrong. For example, the water (vapor) flow direction of the stop valve or check valve is opposite to the sign, the valve stem is installed downwards, the horizontally installed check valve is installed vertically, the open-stem gate valve or butterfly valve handle has no open or closed space, and the valve stem is concealed Do not face the inspection door.
as a result of
The valve fails, the switch is difficult to overhaul, and the valve stem faces down often causing water leakage.
Strictly install according to the valve installation instructions. For the rising stem gate valve, leave enough stem to extend the opening height. The butterfly valve fully considers the handle rotation space. Various valve stems cannot be lower than the horizontal position, let alone downward. The concealed valve should not only be equipped with an inspection door that meets the needs of valve opening and closing, but also the valve stem should face the inspection door.
Ordinary valve flanges are used for butterfly valve flanges.
as a result of
Butterfly valve flanges are different in size from ordinary valve flanges. Some flanges have small inner diameters, while butterfly valves have large discs, which can cause damage to the valve due to inability to open or hard opening.
The flange should be processed according to the actual size of the butterfly valve flange.
During the construction of the building structure, no holes and embedded parts are reserved, or the size of the reserved holes is too small and the embedded parts are not marked.
as a result of
In the construction of heating and sanitation engineering, the building structure is cut, and even the stressed steel bars are cut off, which affects the safety performance of the building.
Familiarize yourself with the construction drawings of the heating and sanitation engineering, and actively cooperate with the construction of the building structure to reserve holes and embedded parts according to the needs of the installation of pipelines and supports, and refer to the design requirements and construction specifications for details.
When welding the pipeline, the pipe is not on the same centerline after the aligning, and there is no gap between the aligning, and the thick-walled pipe is not beveled. The width and height of the welding seam do not meet the requirements of the construction specification.
as a result of
The misalignment of the pipe does not directly affect the quality of welding and the quality of perception. No gaps are left in the counterparts, and thick-walled pipes are not beveled. When the width and height of the welding seam do not meet the requirements, the welding cannot meet the requirements of strength.
After welding the pipes, the pipes should not be misaligned. They should be on a center line with a gap between the opposites. For thick-walled pipes, the bevel should be shoveled. In addition, the width and height of the weld should be welded in accordance with the specifications.
The pipeline is directly buried in frozen soil and untreated loose soil, and the spacing and location of the pipeline support piers are improper, even in the form of dry bricks.
as a result of
Due to the unstable support of the pipeline, it was damaged during the tamping process of the backfill, resulting in rework and repair.
The pipeline shall not be buried in frozen soil or untreated loose soil. The spacing of the buttresses must meet the requirements of the construction specification, and the support pads must be firm, especially the pipe joints, and should not bear shearing force. Brick buttresses shall be built with cement mortar to ensure completeness and firmness.
The material of the expansion bolts used to fix the pipe bracket is poor, the hole diameter of the expansion bolts is too large, or the expansion bolts are installed on a brick wall or even a lightweight wall.
as a result of
The pipe support is loose, and the pipe is deformed or even falls off.
Expansion bolts must be qualified products. If necessary, samples should be tested and inspected. The hole diameter of the expansion bolts should not be larger than the outer diameter of the expansion bolts by 2mm. Expansion bolts should be applied to the concrete structure.
The flanges and gaskets of the pipe connection are not strong enough, and the connecting bolts are short or have a small diameter. Heat pipes use rubber pads, cold water pipes use asbestos pads, and double-layer pads or inclined pads, flange pads protruding into the pipe.
as a result of
The flange connection is not tight or even damaged, causing leakage. The flange gasket protruding into the pipe will increase the water flow resistance.
Pipe flanges and gaskets must meet the requirements of the pipeline design working pressure. The flange gaskets of heating and hot water supply pipes should be rubber asbestos gaskets; the flange gaskets of water supply and drainage pipes should be rubber gaskets. The gasket of the flange shall not protrude into the pipe, and its outer circle should reach the bolt hole of the flange. No bevel pads or several gaskets should be placed in the middle of the flange. The diameter of the bolts of the connecting flange should be less than 2mm than the diameter of the flange. The length of the bolt rod and the nut should be 1/2 of the thickness of the nut.
In the hydraulic strength test and tightness test of the piping system, only the pressure value and water level change are observed, and the leakage check is not enough.
as a result of
Leakage occurs after the piping system is in operation, which affects normal use.
When the piping system is tested in accordance with the design requirements and construction specifications, in addition to recording the pressure value or water level change within the specified time, it is especially necessary to carefully check whether there is any leakage problem.
Sewage, rainwater, and condensate pipes are concealed without closing the water test.
as a result of
It may cause water leakage and cause user losses.
The closed-water test work should be checked and accepted in strict accordance with the specifications. Concealed sewage, rainwater, and condensate pipes, etc. buried in the ground, ceilings, pipe rooms, etc., must ensure that there is no leakage.
The pipeline system was not flushed carefully before completion, and the flow rate and speed did not meet the pipeline flushing requirements. It even replaces flushing with water pressure strength test.
as a result of
The water quality does not meet the operating requirements of the pipeline system, which often results in the reduction or blockage of the pipeline cross-section.
Use the maximum set juice flow rate in the system or a water flow velocity that should not be less than 3m/s for flushing. The water color and transparency of the discharge outlet should be consistent with the water color and transparency of the inlet water visually as qualified.
During winter construction, water pressure test is carried out at negative temperature.
as a result of
Due to the rapid freezing in the tube during the water pressure test, the tube was frost-damaged.
Try to carry out a water pressure test before the winter application, and blow off the water after the pressure test, especially the water in the valve must be cleaned, otherwise the valve will freeze and crack. When the water pressure test is carried out in the winter, the project must be carried out at a positive indoor temperature, and the water must be blown off after the pressure test. When the water pressure test cannot be carried out, the test can be carried out with compressed air.
Must pay attention
1. Rising stem valves cannot be directly buried in the ground
To prevent corrosion of the valve stem, it can only be installed in a covered trench. The valve should be installed in a location that is convenient for operation, inspection, disassembly, maintenance and operation.
2. When handling the valve, it is not allowed to throw it at will, so as to avoid damage and deformation
When stacking, carbon steel valves should be separated from stainless steel valves and non-ferrous metal valves. When lifting the valve, the wire rope should be tied to the connecting flange between the valve body and the bonnet, and never tied to the handwheel or valve stem to prevent damage to the valve stem and handwheel.
3. The valve installation position should not hinder the disassembly, maintenance and operation of equipment, pipelines and the valve itself
The installation height should be convenient for operation and maintenance. Generally, the valve handle should be 1-1.2m away from the ground. For valves with more operations, when they must be installed more than 1.8m from the operating surface, a fixed operating platform should be installed. When they must be installed above or below the operating surface, an extension rod should be installed or the valve stem should be installed horizontally. Install a handwheel or remote operation device with a transmission device. The angle between the axis of the valve transmission device should not be greater than 30°, and the joint should be flexible to rotate, flexible and easy to use during operation, and the instructions are accurate. For valves with thermal displacement, the actuator should have compensation measures.
4. For horizontal pipelines, it is best to install the valve vertically upwards or install the valve stem within the upper semicircle, but do not install the valve stem downwards
The valve stem and hand wheel on the vertical pipeline must be installed along the direction of the operating circuit. When possible, the valve should be installed centrally as much as possible to facilitate operation. The valves on the tower area pipelines 4m above the ground should not be installed outside the platform to facilitate installation and operation.
5. For directional valves, the installation direction should be determined according to the medium flow direction of the pipeline during installation
If the shut-off valve is installed, the medium should flow from the bottom of the cabinet to the top, commonly known as low inlet and high outlet.
When installing the cock and gate valve, allow the medium to flow out from either end. When installing a check valve, special attention must be paid to the flow direction of the medium to ensure that the valve disc can automatically open. In important occasions, an arrow should be clearly marked outside the valve body to indicate the flow direction of the medium. For swing check valves, ensure that the rotation pivot of the plug-in plate is installed in a horizontal position. For lift check valves, ensure that the center line of the valve disc is perpendicular to the horizontal plane.
6. For valves with special requirements, be familiar with the installation requirements
For example, when installing a lever-type safety valve and a pressure reducing valve, the center line of the valve disc and the horizontal plane must be perpendicular to each other, and correction must be made when it is found to be tilted.
7. Install the union
When installing a threaded valve on the pipeline, a live joint must be installed near the valve for easy disassembly and assembly.
8. A shut-off valve should be installed when the auxiliary system pipeline enters the workshop
When the workshop is stopped for maintenance, it can be cut off from the main pipeline. The installation height of these valves is generally high and should be arranged together as much as possible in order to set up a fixed operating platform.
9. Install flanged valves
It is necessary to ensure that the end faces of the two flanges connected to it are parallel and coaxial with the valve flange. Especially when installing a valve with a brittle material such as cast iron, it is necessary to avoid damage to the valve due to incorrect installation position and uneven force. When tightening the flange bolts, a symmetrical or crisscross method should be adopted, and the flange bolts should be tightened gradually in several times.
10. Before installing the high-pressure valve, the product certificate and test records must be reviewed
High-pressure valves are mostly angle valves. They are often used in series with two in series. When opened, the starting force is large. A valve frame must be set to support the valve and reduce the starting stress. The installation height is preferably 0.6-1.2m.
11. Pipe connections on pumps, heat exchangers, towers and containers should not bear the weight of valves and pipes. Valves with a nominal diameter dn>80mm should be equipped with brackets.
12. The lining, spraying and non-metallic materials are of high quality and low strength. In addition to considering the process requirements, they should be arranged in a centralized manner as much as possible to facilitate the design of the valve frame.
Even a single valve should be fixed on the valve frame. When installing heavy valves on horizontal pipelines, consider installing brackets on both sides of the valve.
13. Valves installed with threaded connections should ensure that the threads are intact
The packing should be selected according to the working conditions, and the position of the valve stem should meet the installation requirements when tightened in place. When tightening, a wrench must be used to bite and tighten the valve hexagon at one end of the pipe to ensure that the valve body will not be deformed or damaged. Flange or threaded valves should be installed in the closed state.
14. The bottom welding of the welding seam of the welding valve and the pipeline should be welded by argon arc welding to ensure its internal smoothness and cleanliness.
The valve should not be closed during welding to prevent overheating and deformation of the sealing surface. If the sealing material is not resistant to high temperatures, remove the sealing material before welding to prevent the high temperature from damaging the sealing material.
15. For valves on side-by-side pipelines, the clear distance between handwheels shall not be less than 100mm. In order to reduce the pipe spacing, it is best to stagger the side-by-side valves.
16. The cryogenic valve should be opened and closed as far as possible in the cold state before positioning, and it is required to be flexible and free from jamming.
17. The connection of the safety valve should have an elbow (or three-way accessories)
Avoid fluid directly impacting the valve; in addition, ensure that the safety valve does not form frost during operation to avoid failure during operation.
18. It is strictly forbidden to use the valve stem as a scaffold to climb when the valve is installed.
19. High temperature valve above 200℃
Since the valve is installed at normal temperature, and after normal use, the temperature rises, the valve bolts are heated to expand, and the gap increases, so they must be tightened again, which is called “hot tightening”. The operator should pay attention to this work, otherwise valve leakage will easily occur. event.
20. When the water valve is closed for a long time when it is cold in winter, the accumulated water behind the valve should be removed
After the steam valve stops, the condensed water should also be removed. The bottom of the valve is like a drain switch, which can be opened to drain.
21. Non-metal valves, some are hard and brittle, and some are low in strength. During operation, the opening and closing force should not be too large, especially not strong. Also pay attention to avoid object bumps.
22. The flow direction of the shut-off valve during installation should be consistent with the arrow marked on the valve body (cannot be installed backwards)
When the valve is closed, the pressure is added to the cone at the top of the valve, and the packing is not loaded. However, for valves that do not open and close frequently but need to be strictly ensured that they do not leak in the closed state (such as heating valves), they can be consciously reverse-installed according to requirements to make them tightly closed with the help of medium pressure.
23. Large-size gate valves (DN200-500MM) and pneumatic control valves should be installed vertically
To prevent the valve core from being biased to one side due to its large weight, increasing the mechanical wear between the valve core and the bushing, and causing leakage.
23. When tightening the compression screw, the valve should be in a slightly open state to avoid crushing the sealing surface of the valve top.
24. After all the valves are in place, they should be opened and closed again, and they are qualified if they are flexible and not stuck.
25. After the large air separation tower is bare-cooled, the flange of the connecting valve is pre-tightened once in the cold state to prevent the valve from leaking at room temperature and leaking at the low temperature of the valve.
26. When the new valve is in use, the packing should not be too tightly pressed, so as not to leak, so as to avoid too much pressure on the valve stem, accelerated wear, and strenuous opening and closing.