Installation technology: boiler pipe valve installation pipe valve installation should pay attention to the following three points

Installation technology: boiler pipe valve installation pipe valve installation should pay attention to the following three points

(1) Before installation of all kinds of valves, check the following: whether the packing materials meet the design requirements and whether the packing method is correct. Valve stem at packing seal is corroded. Whether the switch is flexible and the indication is correct.
1. Check the valve before installation
After the valve is selected correctly, it must be installed correctly so as to maximize its effectiveness. But the valve should be installed before the inspection and inspection.
(1) Check the following before installation of all types of valves:
Whether the filler material meets the design requirements, and whether the filler method is correct.
Valve stem at packing seal is corroded.
Whether the switch is flexible and the indication is correct.
Casting valve appearance without obvious manufacturing defects.
(2) The tightness must be checked before installation
As a closed component of the valve (acting as an isolation function), must be installed before the tightness test, to check the seat and the valve core, cover and packing chamber of the combination of tightness. The tightness test of the valve shall be conducted at 1.25 times the pressure of the nameplate.
For the safety door or nominal pressure is less than or equal to 0.6Mpa and nominal diameter is greater than or equal to 800mm of the valve, color printing can be used to check the tightness of the valve core sealing surface.
For large diameter welded valves with nominal diameter greater than or equal to 600mm, oil or water seepage can be used instead of water pressure tightness test.
Before the valve tightness test, it is strictly prohibited to have grease and other coatings on the bonding surface.
Valve tightness hydraulic test should be in line with the manufacturer’s regulations, the test of the globe valve, water should be introduced from the top of the valve disc; For the test of gate valve, the valve should be closed and the sealing surface should be checked.
After the tightness test of the valve is qualified, the valve should be closed and the sealing surface should be checked.
(3) Spot check must be carried out before installation
The low-pressure valve shall be inspected for tightness test by no less than 10% (at least one) in each batch (same manufacturer, same specifications, same model). If it is unqualified, it shall be inspected one by one if it is still unqualified after random inspection by 20%.
Valves for high pressure pipelines should be checked for tightness one by one.
(4) Disassembly inspection of valve before installation
The following valves must be disassembled and inspected before installation:
a. Valves designed for temperature greater than or equal to 450℃.
b. Safety and throttle valves.
c. Valves with unqualified tightness test.
Before the valve disassembly, the dirty dirt should be cleaned, otherwise, the opening and closing operation and disassembly should not be carried out. When the valve of special structure is disassembled and inspected, the disassembly should be carried out in accordance with the disassembly sequence specified by the manufacturer to prevent damage to parts or affect personal safety.
The following checks should be made on the disintegrated valve:
a. The internal parts of alloy steel valves shall be reviewed by spectra (no marks shall be made on the parts, but the inspection results shall be recorded).
b. Whether the valve seat is firmly combined with the valve shell, and whether there is loosening phenomenon.
c. Whether the joint surface of the valve core and the valve seat is compatible, and whether the joint surface is defective.
d. Whether the stem is flexibly connected to the spool.
e. Whether the valve stem is bent, corroded, whether the valve stem and the packing gland fit together properly, and whether the screw thread on the valve stem is broken or not.
f. Joint of flange face of valve cover.
g. Check the opening and closing stroke and terminal position of the throttle valve, and mark it as far as possible.
(5) The valve shall meet the following quality requirements after disintegration inspection and elimination of defects
The material of alloy steel parts meets the design requirements.
Assemble correctly, move flexibly, and the opening indicator indicates correctly.
The specifications and quality of the gasket and packing meet the technical requirements.
Fill the packing materials correctly and cut the interfaces into diagonal holes. The interfaces on each layer should be staggered. Packing should be compressed to ensure tightness, and do not hinder the stem opening and closing.
(6) Valves of the oil system. Valves used in oil systems should be cleaned in their flow through parts, sand and paint should be removed, and oil resistant pan roots and gaskets should be replaced.
(7) Valve reassembly inspection and inspection
When the gate valve and globe valve are reassembled after being disassembled and qualified, the disc must be in the open position before the valve cover bolt can be tightened.
The valve shall be tested for tightness after disassembly and reassembly.
The operating mechanism and transmission device of the valve should be checked and adjusted according to the design requirements to achieve flexible action and correct instructions.
(8) All kinds of valves, when the manufacturer ensures product quality and provides product quality and use guarantee, do not do disintegration and tightness inspection, otherwise should be checked and tested.
Two, valve installation process
The quality of valve installation directly affects the use, so careful attention must be paid to it.
(1) Direction and position
The direction of the valve.
Many valves have directivity, such as globe valve, throttle valve, pressure reducing valve, check valve, etc., if inverted installation reverse, it will affect the use effect and life (such as throttle valve), or do not work at all (such as pressure reducing valve), and even cause danger (such as check valve). General valves have direction marks on the valve body; If not, it should be correctly identified according to the working principle of the valve.
The valve chamber of the globe valve is not symmetrical, the fluid should let it from the bottom to the valve port, so that the fluid resistance is small (determined by the shape), open the force saving (because of the medium pressure up), closed after the medium does not pressure packing, easy to repair, this is the globe valve can not be installed reverse truth. Other valves also have their own characteristics.
Valve installation position
Valve installation position, must be easy to operate; Timely installation is temporarily difficult, but also for the sake of the long-term work of the operator. Valve handwheel handwheel is better with the chest (generally 1.2m away from the operating floor), so. It is easier to open and close the valve. Landing valve handwheel should be upward, do not tilt, so as to avoid awkward operation. Against the wall and against the valve of the equipment, there should also be room for the operator to stand. To avoid the operation of the sky, especially acid and base, toxic media, otherwise it is not safe.
A. Gate valve should not be inverted (that is, handwheel down), otherwise the medium will be retained in the valve cover space for a long time, easy to corrosion the stem, and for some process requirements taboo, at the same time it is very inconvenient to replace the packing.
b. Open stem gate valve, do not install underground, otherwise due to damp corrosion exposed stem.
c. Lift check valve, when installing to ensure that the disc vertical, so that flexible lifting.
d. Swing check valve, when installed to ensure that the pin level, so that flexible swing.
e. The pressure reducing valve shall be installed upright on the horizontal pipe, and shall not be tilted in any direction.
(2) Installation process
Care must be taken during installation and construction to avoid hitting valves made of brittle materials.
Before installation, the valve should be checked, check the specifications, identify whether there is damage, especially for the valve stem, but also rotate a few times to see whether it is skewed, because in the process of transportation, it is easy to bump the crooked valve stem, but also the debris in the valve.
When lifting the valve, the rope should not be tied to the handwheel or stem to avoid damage to these parts, should be tied to the flange.
For the valve connected to the pipeline, be sure to clean, can be compressed air to blow away iron oxide scraps, sand, welding slag and other debris. These sundries are not only easy to scratch the sealing surface of the valve, among which large particles of sundries (such as welding slag) can also block the small valve and make it fail.
When installing the screw valve, the sealing packing (thread and lead oil or polytetrafluoroethylene raw material belt) should be wrapped on the pipe thread, do not get into the valve, so as not to valve memory volume, affect the flow of media.
When installing flange valves, be careful to tighten the bolts symmetrically and evenly. Valve flange and pipe flange must be parallel, reasonable clearance, so as to avoid excessive pressure, or even cracking of the valve, for brittle materials and strength is not high, especially pay attention to the valve.
The valves that need to be welded with pipes should be spot-welded first, then the closing parts should be fully opened, and then welded dead.
(3) Valve insulation facilities
Some valves also need external protection, that is, insulation and cooling. Heating steam lines are sometimes added to the insulation layer.
Whether the valve needs to be insulated or kept cold should be determined according to the production requirements.
Protection principle: where the medium in the valve reduces the temperature too much, it will affect the production efficiency or freeze the valve, it needs heat preservation or even with heat; Where the valve is exposed, adverse to production or cause frost and other adverse phenomena, it is necessary to keep cold. For personal safety and production efficiency, when the valve temperature of the power plant exceeds 50℃, it must be equipped with thermal insulation facilities.
If the water is not used for a long time, the steam valve must discharge the water.
(4) Bypass and instrument
Some valves in addition to the necessary protection facilities, but also have bypass and instrumentation, bypass installation to facilitate trap maintenance. Other valves, also have the installation of bypass. Whether to install the bypass depends on the valve condition, importance and production requirements.
(5) Replacement of packing
Reasons for packing replacement
a. Inventory valves, some packing is not good, some with the use of media does not match, need to replace the packing.
b. Valve manufacturer can not consider the use of the medium used by the unit, the packing box is always filled with ordinary root, but when used, the packing must be adapted to the medium.
Packing replacement process
a. When replacing the filler, press it in round by round.
b. It is appropriate for each round seam to be 45°, and the round seam should be staggered 180°.
c. The packing height should consider the room for continued pressing of the gland. At present, the depth of the packing chamber under the gland should be appropriate, which can be 10%~20% of the total depth of the packing chamber.
d. For high demand valves, the joint Angle is 30°. The joints between the rings are staggered by 120°.
E. processing the above packing, can also according to the specific situation, USES the rubber o-ring (natural rubber resistant to weak base under 60 ℃, nitrile butadiene rubber oil resistant under 80 ℃, fluorine rubber resistance to a variety of corrosive medium under 150 ℃) three lap ptfe ring (below 200 ℃) strong corrosive medium resistance nylon bowl ring (ammonia under 120 ℃, alkali resistant) forming filler. A layer of polytetrafluoroethylene (PTFE) raw material tape is wrapped around the common asbestos disc, which can improve the sealing effect and reduce the electrochemical corrosion of the valve stem.
f. When pressing the packing, rotate the valve stem at the same time to keep the circumference uniform and prevent too dead. Tighten the gland with even force and do not tilt.
Pipe valve installation should pay attention to the following three points
Pipe valve installation should pay attention to the following three points
First, we must pay attention to check before installation
1. Carefully check whether the valve model and specification meet the requirements of the drawing.
2. Check whether stem and disc are opened flexibly, and whether they are stuck or skewed.
3. Check whether the valve is damaged and whether the thread of the valve is correct and intact.
4. Check whether the combination of seat and valve body is firm, disc and seat, cover and valve body, stem and disc connection.
5. Check whether the valve padding, packing and fasteners (bolts) are suitable for the requirements of the nature of the working medium.
6. The old or long used pressure reducing valve should be removed, dust, sand and other debris must be cleaned with water.
7. Through the cover, check the sealing degree, the valve disc must be closed tightly.
4. The screw thread should be guaranteed intact and wrapped with hemp, lead oil or polytetrafluoroethylene tape on the thread. When screwing, the wrench should be stuck into the hexagonal valve body at one end of the pipe.
5. When installing the flange valve, pay attention to tighten the connection bolt along the diagonal direction, and the force should be uniform when screwing to prevent the gasket from deviating or causing deformation and damage to the valve body.
6. The valve should be kept closed during installation. For threaded valves close to the wall, the installation often needs to remove the stem, disc and hand wheel, to turn. Disassembly should be carried out after twisting the hand wheel to keep the valve open.