1. Orientation and location
Many valves are directional
Such as globe 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 create a hazard (eg check valve). Generally, the valve has a direction mark on the valve body. If not, it should be correctly identified according to the working principle of the valve.
The valve cavity of the globe 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 pressure of the medium 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 cannot be reversed. Other valves also have their own characteristics.
The valve installation location must be easy to operate
Even if the installation is temporarily difficult, consider the long-term work of the operator. It is better to align the valve handwheel with the chest (usually 1.2 meters away from the operating floor), so that it is easier to open and close the valve. The handwheel of the landing valve should be upward, not inclined, so as to avoid awkward operation. The valve of the machine against the wall should also leave room for the operator to stand.
It is necessary to avoid operation in the sky, especially acid and alkali, toxic media, etc., otherwise it is very unsafe.
The gate should not be installed upside down (that is, the handwheel is downward), otherwise the medium will remain in the valve cover space for a long time, which will easily corrode the valve stem, and is prohibited by certain process requirements. It is extremely inconvenient to replace the packing at the same time. The rising stem gate valve should not be installed underground, otherwise the exposed valve stem will be corroded due to moisture.
When installing the lift check valve, ensure that its disc is vertical so that it can be lifted flexibly. When installing the swing check valve, ensure that its pin shaft is level so that it can swing flexibly. The pressure reducing valve should be installed upright on the horizontal pipeline, and should not be inclined in all directions.
2. Construction work
Installation and construction must be careful, avoid hitting the valve made of brittle material.
All valve models and specifications should be carefully checked for compliance with design requirements.
(According to the valve model and factory manual, check whether they can be applied under the required conditions, and do a hydrostatic or pneumatic test if necessary.)
In addition, it should also be checked whether the packing is in good condition, whether the gland bolts have sufficient adjustment margin, and whether the valve stem and valve disc are smooth, whether they are stuck or skewed.
(The sealing surface of the valve disc must be tightly closed, and the quality of the threads should be checked for valves connected with threads. Unqualified valves cannot be installed, and should be stacked or marked separately.)
Remove debris from the valve.
When the valve is lifted, the rope should not be tied to the handwheel or valve stem to avoid damage to these parts, and should be tied to the flange.
For the pipeline connected to the valve, be sure to clean it.
Compressed air can be used to blow off iron oxide filings, sediment, welding slag and other debris. These debris not only easily scratch the sealing surface of the valve, but also block the small valve and make it invalid.
When installing the screw valve, the sealing packing (line hemp plus aluminum oil or PTFE raw material tape) should be wrapped on the pipe thread, and do not get into the valve, so as to avoid accumulation in the valve and affect the flow of the medium.
When installing flanged valves, pay attention to tightening the bolts symmetrically and evenly. The valve flange and the pipe flange must be parallel with a reasonable gap to avoid excessive pressure or even cracking of the valve. Special attention should be paid to brittle materials and valves with low strength. Valves that must be welded to the pipe should be spot welded first, then the closing parts should be fully opened, and then welded to death.
3. Protective measures
Some valves must also have external protection, which is heat preservation and cold preservation. Sometimes a hot steam line is added to 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 lowers the temperature too much, which will affect the production efficiency or freeze the valve, it needs to be kept warm, or even heated; when the valve is exposed, it is unfavorable to production or causes adverse phenomena such as frost, it needs to be kept cold. Insulation materials include asbestos, slag wool, glass wool, perlite, diatomite, vermiculite, etc.; cold insulation materials include cork, perlite, foam, plastic, etc.
4. Bypass and instrumentation
For some valves, in addition to the necessary protection facilities, there are also bypasses and instruments. Bypass installed. Easy to repair the trap. Other valves also have bypasses installed. Whether to install a bypass depends on the valve condition, importance and production requirements.
5. Packing replacement
In stock valves, some packings are no longer good, and some are not in line with the medium used, which requires replacement of packings.
The valve manufacturer cannot consider the use of thousands of different media. The stuffing box is always filled with ordinary packing, but when using it, the packing must be adapted to the medium.
When replacing the packing, press it in circle by circle. The seam of each circle is preferably 45 degrees, and the circle and the circle are connected by 180 degrees. The packing height should consider the room for the gland to continue to be pressed, and now let the lower part of the gland press the packing chamber to an appropriate depth, which 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, rubber O-rings (natural rubber resistant to weak alkalis below 60 degrees Celsius, nitrile rubber resistant to oil crystals below 80 degrees Celsius, and fluororubber resistant to various corrosive media below 150 degrees Celsius) can be stacked in three pieces according to specific conditions. Forming fillers such as PTFE ring (resistant to strong corrosive medium below 200 degrees Celsius) nylon bowl ring (resistant to ammonia and alkali below 120 degrees Celsius).
Outside the ordinary asbestos packing, wrap a layer of PTFE raw material tape, which 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 circumference even and prevent it from being too dead. Tighten the gland with even force and not tilt.
14 taboos for valve installation
1. Taboo: The main materials, equipment and products used in construction lack technical quality appraisal documents or product qualification certificates that meet the current standards issued by the state or the ministry.
Consequences: The quality of the project is unqualified, there are hidden dangers of accidents, and it cannot be delivered for use on schedule, so it must be reworked and repaired; resulting in delays in the construction period and increased investment in labor and materials.
Measures: The main materials, equipment and products used in water supply and drainage and heating and sanitary projects should have technical quality appraisal documents or product qualification certificates that meet the current standards issued by the state or the ministry; their product names, models, specifications, and national quality standards should be marked. Code, date of manufacture, name and location of the manufacturer, inspection certificate or code of the manufactured product.
2. Taboo: The necessary quality inspection is not carried out according to the regulations before the valve is installed.
Consequences: During the operation of the system, the valve switch is not flexible, the closing is not strict and water (steam) leakage occurs, resulting in rework and repair, and even affecting the normal water supply (steam).
Measures: Before the valve is installed, the compressive strength and tightness test should be done. For the test, 10% of the quantity of each batch (same brand, same specification, same model) shall be randomly checked, and not less than one. For the closed-circuit valve installed on the main pipe to cut off, the strength and tightness test shall be carried out one by one. The strength and tightness test pressure of the valve shall comply with the “Code for Acceptance of Construction Quality of Building Water Supply and Drainage and Heating Engineering” (GB 50242-2002).
3. 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 for the water supply branch pipe when the pipe diameter is less than or equal to 50mm; the stop valve is used for the dry and riser 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 adjust the resistance, pressure and other functions. Even caused the valve to be damaged and forced to be repaired during the operation of the system.
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 should 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, the stop valve should be used; when the pipe diameter is greater than 50mm, the gate valve should be used.
Hot water heating dry and vertical control valves should use gate valves, and fire pump suction pipes should not use butterfly valves.
4. Taboo: the valve installation method is wrong. For example, the water (steam) flow direction of the globe valve or check valve is opposite to the sign, 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 or closing space, and the valve stem of the concealed valve is installed. Not towards the inspection door.
Consequences: the valve fails, the switch is difficult to repair, and the valve stem is facing down, which often causes water leakage.
Measures: Strictly follow the valve installation instructions for installation, leave enough valve stem to extend the opening height of the open stem gate valve, fully consider the handle rotation space for the butterfly valve, and the various valve stems cannot be lower than the horizontal position, let alone downward. For concealed valves, not only should an inspection door meet the needs of valve opening and closing, but also the valve stem should face the inspection door.
5. Taboo: Butterfly valve flanges use ordinary valve flanges.
Consequences: Butterfly valve flanges are different in size from ordinary valve flanges. Some flanges have a small inner diameter, while the disc of the butterfly valve is large, resulting in failure to open or hard opening and damage to the valve.
Measures: Process the flange according to the actual size of the butterfly valve flange.
6. Taboo: There are no reserved holes and embedded parts in 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 sanitary engineering, the building structure is chiseled, and even the stressed steel bars are cut off, which affects the safety performance of the building.
Measures: Familiarize yourself with the construction drawings of the heating and sanitary 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 pipes and supports and hangers, and refer to the design requirements and construction specifications for details.
7. Taboo: When the pipeline is welded, the staggered joints of the pipes are not on the same center line after the counterparts, no gaps are left for the counterparts, and the thick-walled pipes are not shoveled, and the width and height of the welds do not meet the requirements of the construction specification.
Consequences: the misalignment of the pipe directly affects the welding quality and visual quality. No gap is left between the counterparts, thick-walled pipes are not shoveled, and the welding seam width and height do not meet the requirements.
Measures: After welding the counterparts of the pipes, the pipes should not be staggered. They should be on the same center line, and the counterparts should be left with a gap. Thick-walled pipes should be beveled. In addition, the width and height of the weld should be welded according to the specifications.
8. Taboo: The pipeline is directly buried on the frozen soil and untreated loose soil, and the spacing and position of the pipeline piers are improper, even in the form of dry yard bricks.
Consequences: Due to the unstable support, the pipeline was damaged during the backfill compaction process, resulting in rework and repair.
Measures: The pipeline shall not be buried on the frozen soil and untreated loose soil, the spacing of the piers shall meet the requirements of the construction specification, and the support pads shall be firm, especially the joints of the pipelines, which should not be subjected to shearing force. Brick buttresses shall be built with cement mortar to ensure integrity and firmness.
9. Contraindications: The material of the expansion bolts for fixing the pipe supports is poor, 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 pipe support is loose, the pipe is deformed, or even falls off.
Measures: Qualified products must be selected for expansion bolts. If necessary, samples should be taken for test inspection. The diameter of the installation expansion bolts should not be greater than the outer diameter of the expansion bolts by 2mm. The expansion bolts should be used on concrete structures.
10 Taboos: The flanges and gaskets of the pipeline connection are not strong enough, and the connecting bolts are short or small in diameter. Rubber pads are used for heat pipes, asbestos pads are used for cold water pipes, and double-layer pads or inclined pads are used, and the flange gaskets protrude into the pipes.
Consequences: The flange connection is not tight, or even damaged, and leakage occurs. Flange gaskets protrude into the pipe, increasing the resistance to water flow.
Measures: The flanges and gaskets used for the pipeline must meet the requirements of the design working pressure of the pipeline. Rubber asbestos gaskets should be used for flange gaskets of heating and hot water supply pipes; rubber gaskets should be used for flange gaskets of water supply and drainage pipes.
The gasket of the flange shall not protrude into the pipe, and its outer circle should reach the bolt hole of the flange. No inclined surface pads or several pads shall be placed in the middle of the flange. The diameter of the bolt of the connecting flange should be less than 2mm than the diameter of the flange plate, and the length of the nut protruding from the bolt rod should be 1/2 of the thickness of the nut. ,
11 Taboo: During the hydraulic strength test and tightness test of the pipeline system, only the pressure value and the water level change are observed, and the leakage inspection is not enough.
Consequences: leakage occurs after the operation of the pipeline system, which affects the normal use.
Measures: When the pipeline system is tested according to the design requirements and construction specifications, in addition to recording the pressure value or the water level change within the specified time, it is especially necessary to carefully check whether there is any leakage problem.
12. Taboo: Sewage, rainwater and condensate pipes are concealed without closed water test.
Consequences: It may cause water leakage and cause user losses.
Measures: The closed water test work should be checked and accepted in strict accordance with the specifications. Buried underground, in the ceiling, between pipes and other hidden sewage, rainwater, condensate pipes, etc. should be installed to ensure no leakage.
13. Taboo: flushing is not done carefully before the completion of the pipeline system, and the flow and speed cannot meet the requirements of pipeline flushing. Even flushing is replaced by water pressure test drainage.
Consequences: the water quality does not meet the operating requirements of the pipeline system, which often results in the reduction or blockage of the pipeline section.
Measures: Flush with a larger juice flow rate in the system or a water flow rate that should not be less than 3m/s. The water color and transparency of the outlet should be visually consistent with the water color and transparency of the inlet water.
14. Taboo: In winter construction, perform hydraulic test at negative temperature.
Consequences: The tube freezes due to the rapid freezing of the tube during the hydrostatic test.
Measures: try to carry out the water pressure test before winter application, and blow the water after the pressure test, especially the water in the valve must be cleaned, otherwise the valve will crack. When the water pressure test is carried out in winter, the project must be carried out at a positive indoor temperature, and the water must be blown out after the pressure test. When the hydrostatic test cannot be carried out, the test can be carried out with compressed air.
Three, valve installation must pay attention
1. The rising stem valve cannot be directly buried in the ground
To prevent the valve stem from rusting, it can only be installed in a covered trench, and the valve should be installed in a position that is convenient for operation, inspection, disassembly, maintenance and operation.
2. When handling the valve, it is not allowed to throw it at will to avoid damage and deformation
When stacking, carbon steel valves should be separated from stainless steel valves and non-ferrous metal valves. When the valve is hoisted, the steel wire rope should be tied to the connecting flange of the valve body and the bonnet, not to the handwheel or valve stem to prevent damage to the valve stem and handwheel.
3. The installation position of the valve should not hinder the disassembly, maintenance and operation of the equipment, pipeline and 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 many operations, when they must be installed above 1.8m from the operating surface, a fixed operating platform should be set. When they must be installed above or below the operating surface, an extension rod should be set or the valve stem should be installed horizontally, and at the same time Install a handwheel or remote operating device with a transmission.
The included angle of the axis of the valve transmission device should not be greater than 30°. For valves with thermal displacement, the transmission should have compensation measures.
4. For horizontal pipelines, it is better 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 handwheel on the vertical pipeline must be installed along the direction of the operation circuit. When possible, the valve should be installed as centrally as possible to facilitate operation. Valves on tower pipelines that are more than 4m above the ground should not be set outside the platform to facilitate installation and operation.
5. For directional valves, the installation direction should be determined according to the flow direction of the medium in the pipeline.
If the stop valve is installed, the medium should flow from the bottom of the cabinet to the top, commonly known as low in and high out.
When installing the cock and gate valve, allow the medium to flow out from either end. When installing the check valve, special attention must be paid to the flow direction of the medium to ensure that the valve disc can be opened automatically. In important occasions, an arrow should be clearly marked on the valve body to indicate the flow direction of the medium.
For swing check valves, ensure that the pivot of the insert plate is installed in a horizontal position. For the lift check valve, the centerline of the valve disc should be 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 must be perpendicular to the horizontal plane, and correction must be made when it is found to be inclined.
7. Install the union
When installing a threaded valve on a pipeline, a union must be installed near the valve to facilitate disassembly.
8. A shut-off valve should be set when the auxiliary system pipeline enters the workshop
When the workshop is shut down 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
Make sure that the two flange end faces connected to it are parallel and coaxial with the valve flange. Especially when installing valves with brittle materials such as cast iron, valve damage due to incorrect installation position and uneven force should be avoided. When tightening the flange bolts, the symmetrical or criss-cross method should be used, and tighten gradually in several times.
10. Before installing high-pressure valves, the product certificate and test records must be reviewed
Most of the high-pressure valves are angle valves, which are usually connected in series. When opening, 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. The pipe joints on the pump, heat exchanger, tower and container should not bear the weight of the valve and pipeline, and the valve with the nominal diameter dn>80mm should be equipped with a bracket.
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 fastened to the valve frame. When installing heavy-duty valves on horizontal pipes, consider installing brackets on both sides of the valve.
13. Valves with threaded connections should be installed to 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 it is tightened in place. When tightening, you must use a wrench to firmly bite the hexagonal valve at one end of the pipe to ensure that the valve body will not be deformed and damaged. Flanged or threaded valves should be installed in the closed state.
14. The back cover welding of the welding seam between the welded valve and the pipeline should be welded by argon arc welding to ensure that the interior is smooth and clean.
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 temperature, the sealing material should be removed before welding to prevent the sealing material from being damaged by the high temperature of welding.
15. For the valves on the side-by-side pipeline, the clear distance between the handwheels shall not be less than 100mm. In order to reduce the distance between the pipelines, the valves arranged side-by-side should be arranged in a staggered arrangement.
16. Before positioning the low temperature valve, the opening and closing test should be done in a cold state as much as possible, and it is required to be flexible and free from jamming.
17. There should be elbows (or fittings such as tee) at the connection of the safety valve.
Avoid direct impact of fluid on the valve; in addition, ensure that the safety valve is not frosted during operation, so as 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 room temperature, but after normal use, the temperature rises, the valve bolts are heated to expand, and the gap increases, so it must be tightened again, which is called “hot tightening”. The operator should pay attention to this work, otherwise it is prone to valve leakage, etc. event.
20. When it is cold in winter, the water valve is closed for a long time, and the water behind the valve should be removed
After the steam valve is stopped, the condensed water should also be removed. The bottom of the valve is like a drain switch, which can be turned on to drain.
21. 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 object collision.
22. The flow direction of the globe valve during installation should be consistent with the arrow marked on the valve body (it cannot be installed backwards)
When the valve is closed, the pressure is applied to the cone at the top of the valve, and the packing is not loaded. However, for valves (such as heating valves) that are not frequently opened and closed but need to be strictly guaranteed not to leak in the closed state (such as heating valves), they can be consciously installed in reverse according to the needs to make them tightly closed with the help of medium pressure.
23. Large-sized 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 self-weight, increasing the mechanical wear between the valve core and the bushing, resulting in 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 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 exposed to cold, pre-tighten the connecting valve flange once in a cold state to prevent the valve from leaking at room temperature but leaking at low temperature.
26. When the new valve is in use, the packing should not be pressed too tightly, so as not to leak, so as to avoid too much pressure on the valve stem of the valve, accelerated wear, and laborious opening and closing.