Key knowledge of valve installation
Release time:
2019-05-16
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Such as globe valves, throttle valves, pressure reducing valves, check valves, etc., if they are installed in reverse, it will affect the use effect and life (such as throttle valves), or do not work at all (such as pressure reducing valves), or even cause danger (such as check valves).
1. Direction and location
Many valves are directional
Such as globe valves, throttle valves, pressure reducing valves, check valves, etc., if they are installed in reverse, it will affect the use effect and life (such as throttle valves), or do not work at all (such as pressure reducing valves), or even cause danger (such as check valves). General valves, there are directional signs on the valve body. In case 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 be allowed to pass through the valve port from the bottom up, so that the fluid resistance is small (determined by the shape), the opening is labor-saving (due to the upward pressure of the medium), and the medium does not press the packing after closing, which is convenient for maintenance, which is why the globe valve cannot be reversed. Other valves also have their own characteristics.
The valve must be installed in such a way that it can be easily operated
Even if the installation is difficult for the time being, it is necessary to think about the long-term work of the operator. It is best to take the valve handwheel and the chest (generally 1.2 meters away from the operating floor), so that the opening and closing of the valve is more effortless. The handwheel of the floor valve should be facing upwards and not inclined to avoid awkward operation. The wall machine is close to the valve of the equipment, and the operator should also be allowed to stand.
It is necessary to avoid the operation of looking up to the sky, especially acid, alkali, toxic media, etc., otherwise it is very unsafe.
The gate should not be installed upside down (i.e., the handwheel is downward), otherwise the medium will remain in the bonnet space for a long time, which is easy to corrode the valve stem, and is contraindicated by some process requirements. It is extremely inconvenient to change the packing at the same time. Open rod gate valves, do not install underground, otherwise the exposed stem will be corroded due to moisture.
Lifting check valves, when installing to ensure that the disc is vertical, so that the lifting is flexible. Swing check valve, when installed, to ensure that its pin is level, so that the swing is flexible. The pressure reducing valve should be installed upright on the horizontal pipe and should not be tilted in all directions.
2. Construction work
Care must be taken in the installation and construction, and the valve made of brittle materials must not be hit.
Before installation
Carefully check whether the models and specifications of all valves meet the design requirements.
(Check whether they can be used under the required conditions according to the valve model and factory instructions, and perform a water or air pressure test if necessary.) ）
In addition, it is also necessary to check whether the packing is in good condition, whether the gland bolt has sufficient adjustment margin, and check whether the valve stem and valve disc are flexible, whether there is jamming and skewing.
(The sealing surface of the valve disc must be closed tightly, and the threaded quality should be checked for the threaded valve.) Unqualified valves cannot be installed and should be stacked or marked separately. ）
Remove debris from the valve.
Installation process
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 to which the valve is connected, be sure to clean it.
Compressed air can be used to blow off iron oxide filings, sediment, welding slag and other debris. These debris are not only easy to scratch the sealing surface of the valve, but also large particles of debris (such as welding slag) can also block the small valve and make it fail.
When installing the screw valve, the sealing packing (linen plus aluminum oil or PTFE raw meal belt) should be wrapped on the pipe thread, and do not get into the valve, so as to avoid the accumulation in the valve and affect the flow of the medium.
When installing the flange valve, pay attention to the symmetrical and even tightening of the bolts. The valve flange and the pipe flange must be parallel and the clearance must be reasonable, so as to avoid excessive pressure and even cracking of the valve. This is especially the case with brittle materials and valves that are not very strong. Valves that must be welded to pipes should be spot welded first, and then the shut-off parts should be fully opened, and then welded to death.
3. Protective measures
Some valves also have to be protected externally, which is thermal insulation and cold insulation. In the insulation layer, it is sometimes necessary to add hot steam lines. What kind of valve should be insulated 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 is necessary to keep warm, or even mix heat; where the valve is exposed, it is not conducive to production or causes frost and other undesirable phenomena, it is necessary to keep cold. Thermal insulation materials include asbestos, slag wool, glass wool, perlite, diatomaceous earth, vermiculite, etc., and cold insulation materials include cork, perlite, foam, plastic, etc.
4. Bypass and instrumentation
Some valves, in addition to the necessary protection facilities, also have bypasses and instruments. A bypass is installed. Easy access to traps. Other valves are also equipped with a bypass. Whether or not to install a bypass depends on the condition of the valve, its importance and the requirements of production.
5. Packing replacement
Inventory valves, some of the packing is not good, and some are inconsistent with the medium used, which requires the replacement of the filler.
The valve manufacturer cannot consider the use of 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 changing the filler, press it in one by one. The seam of each circle should be 45 degrees, and the circle should be 180 degrees. The packing height should consider the room for the gland to continue to be pressed, and now it is necessary to make the packing chamber at the lower part of the gland at 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 120 degrees.
In addition to the above-mentioned fillers, rubber O-rings (natural rubber resistant to weak alkali below 60 degrees Celsius, nitrile rubber resistant to oil crystals below 80 degrees Celsius, fluoroelastomer resistant to a variety of corrosive media below 150 degrees Celsius) three stacked PTFE rings (resistant to strong corrosive media below 200 degrees Celsius) and nylon bowl rings (resistant to ammonia and alkali below 120 degrees Celsius) and other forming fillers can also be used.
On the outside of ordinary asbestos packing, wrap a layer of PTFE raw tape, which can improve the sealing effect and reduce the electrochemical corrosion of the valve stem. When pressing the seasoning, it is necessary to rotate the valve stem at the same time to keep the surrounding evenness and prevent too much death, and tighten the gland with uniform force and not tilt.
There are 14 taboos for valve installation
1. Contraindications: The main materials, equipment and products used in construction lack technical quality appraisal documents or product 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, it cannot be delivered on time, and it must be reworked and repaired, resulting in the delay of the construction period and the increase of labor and material input.
Measures: The main materials, equipment and products used in water supply and drainage and heating and sanitation projects shall have technical quality appraisal documents or product certificates that meet the current standards issued by the state or the ministry;
2. Contraindications: 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 closure is not strict and the phenomenon of water leakage (steam) 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. The test should be 10% of the quantity of each batch (same brand, same specification, same model), and not less than one. For the closed-circuit valves installed on the main pipe to play a shut-off role, the strength and tightness test should be carried out one by one. The test pressure of valve strength and tightness shall comply with the provisions of the Code for Construction Quality Acceptance of Building Water Supply and Drainage and Heating Engineering (GB50242-2002).
3. Contraindications: 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 pipe diameter of the water supply branch pipe is less than or equal to 50mm, the main and riser pipes of hot water heating are used globe valves, and the suction pipe of the fire pump adopts butterfly valve.
Consequences: Affect the normal opening and closing of the valve and adjust the resistance, pressure and other functions. Even caused the system to operate, the valve was damaged and had to be repaired.
Measures: Be familiar with the application range of various valves, and select the specifications and models of valves according to the requirements of the design. The nominal pressure of the valve should meet the requirements of the system test pressure. According to the requirements of the construction specification: the diameter of the water supply branch pipe is less than or equal to 50mm, and the gate valve should be used when the pipe diameter is greater than 50mm.
Gate valves should be used for hot water heating dry and vertical control valves, and butterfly valves should not be used for fire pump suction pipes.
4. Contraindications: The valve installation method is wrong. For example, the flow direction of water (steam) of the globe 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 open rod gate valve or butterfly valve has no opening and closing space, and the stem of the concealed valve is not facing the inspection door.
Consequences: Valve failure, difficult switch maintenance, and water leakage often caused by the valve stem facing down.
Measures: Install in strict accordance with the valve installation instructions, leave enough valve stem elongation opening height for open rod gate valve, fully consider the handle rotation space for butterfly valve, and various valve rods can not be lower than the horizontal position, let alone down. 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 be facing the inspection door.
5. Contraindications: ordinary valve flanges for butterfly valve flanges.
Consequences: The size of the butterfly valve flange is different from that of the ordinary valve flange, and some of the flanges have a small inner diameter, while the butterfly valve disc is large, resulting in damage to the valve due to the inability to open or hard opening.
Measures: The flange should be processed according to the actual size of the butterfly valve flange.
6. Contraindications: There are no reserved holes and embedded parts in the construction of the building structure, or the size of the reserved holes is small and the embedded parts are not marked.
Consequences: During the construction of the heating and sanitation project, the building structure is chiseled, and even the stressed steel bars are cut off, which affects the safety performance of the building.
Measures: Carefully familiar with the construction drawings of the heating and sanitation project, according to the needs of the installation of pipelines and hangers, take the initiative to seriously cooperate with the reserved holes and embedded parts in the construction of the building structure, and refer to the design requirements and construction specifications.
7. Contraindications: When the pipeline is welded, the wrong mouth of the pipe is not on a center line after the matching, the gap is not left for the match, the groove of the thick-walled pipe is not shoveled, and the width and height of the weld do not meet the requirements of the construction specification.
Consequences: The misalignment of the pipe is not in the center line, which directly affects the welding quality and the quality of perception. There is no gap in the counterpart, the thick-walled pipe does not shovel the groove, and the width and height of the weld do not meet the requirements when the welding cannot meet the requirements of strength.
Measures: After welding the pipeline, the pipe can not be wronged, it should be on a center line, the gap should be left at the counterpart, the thick-walled pipe should be grooved, and the width and height of the weld should be welded in accordance with the requirements of the specification.
8. Contraindications: The pipeline is directly buried in the frozen soil and untreated loose soil, and the spacing and position of the pipeline piers are improper, and even in the form of dry-code bricks.
Consequences: The pipeline suffered damage during the backfill compaction due to unstable support, resulting in rework and repair.
Measures: The pipeline shall not be buried in frozen soil and untreated loose soil, the spacing of the piers shall meet the requirements of the construction specifications, and the support pads shall be firm, especially at the pipeline interface, and shall not bear shear force. The brick piers should be built with cement mortar to ensure integrity and firmness.
9. Contraindications: The expansion bolts fixed the pipe support are of inferior material, and the hole diameter of the expansion bolts is too large or the expansion bolts are installed on the brick wall or even the lightweight wall.
Consequences: Loose pipe supports, deformed pipes, or even falling off.
Measures: Expansion bolts must be selected qualified products, if necessary, sampling should be carried out for test inspection, the hole diameter of the installation of expansion bolts should not be greater than the outer diameter of expansion bolts 2mm, expansion bolts should be applied to concrete structures.
10 Contraindications: The strength of the flange and liner of the pipe connection is not enough, and the connecting bolt is short or the diameter is thin. Rubber pads are used for heating pipes, asbestos pads are used for cold water pipes, and double pads or inclined pads are used, and flange liners protrude into the pipes.
Consequences: The flange connection is not tight, or even damaged, and there is leakage. The flange liner protrudes into the pipe, increasing the resistance to the flow of water.
Measures: Flanges and gaskets for pipelines must meet the requirements of the designed working pressure of pipelines. Rubber asbestos pads should be used for flange liners for heating and hot water supply pipelines, and rubber pads should be used for flange liners for water supply and drainage pipes.
The liner of the flange shall not protrude into the pipe, and its outer circle should be to the flange bolt hole. The bevel pad or several liners shall not be placed in the middle of the flange, the diameter of the bolt connecting the flange should be less than 2mm than the hole diameter of the flange, and the length of the protruding nut of the bolt rod should be 1/2 of the thickness of the nut. 、
11. Contraindications: During the hydraulic strength test and tightness test of the pipeline system, only the pressure value and water level changes 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 water level change within the specified time, it is especially necessary to carefully check whether there is a leakage problem.
12. Contraindications: Sewage, rainwater, and condensate pipes are concealed without a closed water test.
Consequences: May cause water leakage and cause loss to users.
Measures: The closed water test work should be inspected and accepted in strict accordance with the specifications. Underground burial, ceiling, pipe and other concealed sewage, rainwater, condensate pipes, etc. should be guaranteed to be seepage and leakage.
13. Contraindications: The pipeline system is not flushed carefully before completion, and the flow and speed cannot meet the requirements of pipeline flushing. Even a hydrostatic strength test is used to drain water instead of flushing.
Consequences: The water quality does not meet the operational requirements of the pipeline system, which often leads to the reduction or blockage of the pipeline cross-section.
Action: Rinse with the maximum juice flow rate in the system or the water flow rate should not be less than 3m/s. The water color and transparency of the discharge outlet should be consistent with the water color and transparency of the inlet water.
14. Contraindications: Hydraulic test is carried out at negative temperature during winter construction.
Consequences: The tube freezes quickly during the hydrostatic test, causing the tube to freeze.
Measures: Try to carry out the water pressure test before the winter application, and blow the water clean after the pressure test, especially the water in the valve must be cleaned, otherwise the valve will crack. When the project must be tested in winter, it should be carried out at a positive indoor temperature, and the water should be blown clean after the pressure test. When hydrostatic testing is not possible, compressed air can be used for testing.
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