Pipeline valve installation

1 Valve installation position must be convenient for operation

Even if the installation is temporarily difficult, it is necessary to think about the long-term work of the operator. It is best to have the valve handwheel and the chest (usually 1.2 meters away from the operating floor), so that the opening and closing of the valve is more labor-saving. The floor valve hand wheel should be facing up, do not tilt, so as to avoid awkward operation. The valve against the wall machine should also leave room for the operator to stand.

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It is necessary to avoid the operation of the sky, especially acid and alkali, toxic media, etc., otherwise it is very unsafe.
Do not flip the gate (ie, the handwheel is down), otherwise the medium will remain in the bonnet space for a long time, which will easily corrode the valve stem and is contraindicated for certain process requirements. It is inconvenient to replace the packing at the same time Open the gate valve, do not install it in the ground, otherwise the exposed valve stem will be corroded due to moisture.
Lifting check valve, the valve flap should be vertical when installing, so that the lifting is flexible. Swing-type check valve, to ensure the level of its pin when installing, so that the swing is flexible. The pressure relief valve should be installed upright on a horizontal pipe and not tilted in all directions.

2 Construction work

Care must be taken during installation and construction. Do not hit the valve made of brittle material.

Before installation

1. The model and specifications of all valves should be carefully checked to meet the design requirements.
(According to the valve type and factory instructions, check if they can be used under the required conditions, if necessary, for water pressure or air pressure test.)
2. In addition, it should also check whether the packing is intact, whether the gland bolt has sufficient adjustment margin, and whether the valve stem and the valve disc are clear, whether there is any jam or skew.
(The valve disc sealing surface 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.)
3. Remove debris from the valve.

Installation process

1. When the valve is lifted.

The rope should not be attached to the hand wheel or the valve stem to avoid damage to these parts and should be attached to the flange.

2. For the pipeline connected to the valve, be sure to clean it.
Compressed air can be used to blow off iron oxide chips, mud sand, welding slag and other debris. These debris not only easily scratch the sealing surface of the valve, but also large particles (such as welding slag) can also block the small valve and make it invalid.
When installing the screw valve, the sealing packing (line hemp aluminum oil or Teflon raw material tape) should be wrapped on the pipe thread and not in the valve to avoid the valve memory and affect the circulation of the medium.
When installing a flanged valve, pay attention to tightening the bolt symmetrically and evenly. The valve flange and the pipe flange must be parallel and the clearance is reasonable to avoid excessive pressure or even cracking of the valve. Pay particular attention to brittle materials and valves that are not strong enough. The valve to be welded to the pipe shall be spot welded first, then the closing member shall be fully opened and then welded.
3. Protection measures
Some valves must also have external protection, which is insulation and cold preservation. Hot steam lines are sometimes added to the insulation layer. What kind of valve should be kept warm or cold, according to 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, so it needs to be insulated or even mixed with heat; if the valve is exposed, it is unfavorable to production or cause frosting and other undesirable phenomena, it needs to keep cold. Insulation materials are asbestos, slag cotton, glass wool, perlite, diatomaceous earth, vermiculite, etc.; cold insulation materials are cork, perlite, foam, plastic and so on.
4. Bypass and instrument
Some valves, in addition to the necessary protection facilities, also have bypass and instrumentation. A bypass is installed. Easy to repair the trap. Other valves are also installed with bypass. Whether to install the bypass depends on the condition of the valve, the importance and the requirements of the production.
5. Filler replacement
Inventory valves, some fillers are not good, and some do not match the use of media, which requires replacement of fillers.
Valve manufacturers can’t consider using different mediums of thousands of units. The packings are always filled with ordinary packing, but when used, the packing must be adapted to the medium.
When replacing the packing, press it in a circle. The seam is preferably 45 degrees per turn, and the circle and the ring are opened 180 degrees. The height of the packing should consider the room for the gland to continue to be compacted. At present, the packing chamber should be pressed to the appropriate depth of the packing chamber. This depth 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 seam between the circle and the circle is staggered by 120 degrees.
In addition to the above fillers, rubber O-rings can be used according to the specific conditions (natural rubber is resistant to weak alkali below 60 degrees Celsius, nitrile rubber is resistant to oil crystals below 80 degrees Celsius, and fluororubber is resistant to various corrosive media below 150 degrees Celsius) Formed packings such as a stack of PTFE rings (resistant to strong corrosive media below 200 degrees Celsius), nylon bowl rings (resistant to 120 degrees Celsius, ammonia, alkali).
On the outside of the ordinary asbestos packing, a layer of Teflon raw material tape is wrapped to 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 evenly and prevent it from being too dead. To tighten the gland, apply even force and not tilt.

Valve pressure test

For low-pressure, medium-pressure and high-pressure valves, strength tests and tightness tests are to be carried out. Alloy steel valves are also subjected to spectral analysis of the casings one by one, and the materials are reviewed.
1. Strength test of the valve
The strength test of the valve is tested under the open state of the valve to check the leakage of the outer surface of the valve. For valves with PN ≤ 32 MPa, the test pressure is 1.5 times the nominal pressure, the test time is not less than 5 min, and no leakage at the shell and packing gland is acceptable.
2. Valve tightness test
Tests carried out under the condition that the valve is completely closed, check whether there is leakage on the sealing surface of the valve. The test pressure, except the butterfly valve, check valve, bottom valve and throttle valve, should generally be carried out with nominal pressure. At the working pressure, the test can also be carried out with a working pressure of 1.25 times, and the valve sealing surface is not leaked as qualified.

General rules for valve installation

  1. The position of the valve installation should not impede the operation, disassembly and maintenance of the equipment, the pipeline and the valve body itself, and the aesthetic appearance of the assembly should be taken into consideration.
  2. The valve on the horizontal pipe, the valve stem is installed upwards, or it is installed at a certain angle. Do not install the hand wheel downward. The valves, stems and handwheels on the high-altitude pipeline can be installed horizontally, and the valve is opened and closed remotely with a chain that is vertically lower.
  3. Arranged symmetrical, neat and tidy; the valve on the riser, under the premise of the process, the valve hand wheel is most suitable for operation with the chest height, generally 1.0-1.2m from the ground, and the valve stem must follow the operator Directional installation.
  4. The valves on the side-by-side pipe shall have the same centerline elevation and the clearance between the handwheels shall not be less than 100mm; the valves on the side-by-side horizontal pipes shall be staggered to reduce the pipe spacing.
  5. When installing heavier valves on pumps, heat exchangers, etc., valve brackets should be provided; when operating frequently and installed on valves more than 1.8m from the operating surface, a fixed operating platform should be provided.
  6. The valve body has an arrow mark on the valve body, and the direction of the arrow is the flow direction of the medium. When installing the valve, care should be taken to point the arrow at the same direction as the flow in the pipe.
  7. When installing the flange valve, ensure that the end faces of the two flanges are parallel and concentric with each other. Do not use double gaskets.
  8. When installing a threaded valve, a threaded valve should be equipped with a union for easy disassembly. The setting of the joint should consider the convenience of maintenance. Usually, the water flow passes through the valve and then passes through the joint.

Valve installation precautions

  1. The valve body material of the valve is mostly made of cast iron, which is brittle and therefore must not be hit by heavy objects.
  2. When carrying the valve, it is not allowed to throw it at hand; when lifting and lifting the valve, the rope should be attached to the valve body, and it is strictly prohibited to lie on the hand wheel, the valve stem and the flange bolt hole.
  3. The valve should be installed in the most convenient place for operation, maintenance and overhaul. It is strictly prohibited to be buried underground. The valves on the pipes directly buried and in the trench shall be inspected to facilitate the opening and closing and adjustment of the valves.
  4. The thread should be intact and wrapped around the thread, leaded with lead oil or wrapped with Teflon tape. When turning the buckle, use a wrench to clamp the hexagonal valve body screwed into one end of the pipe.
  5. When installing the flange valve, pay attention to tighten the connecting bolt in the diagonal direction. When the screwing is used, the force should be even to prevent the gasket from running off or causing deformation and damage of the valve body.
  6. The valve should remain closed during installation. For threaded valves that are closer to the wall, it is often necessary to remove the stem valve disc and handwheel to install. When disassembling, the handwheel should be turned to keep the valve open, and then disassembled.

14 taboos and solutions for valve installation

Taboo 1: The main materials, equipment and products used in construction lack technical quality identification documents or product certificates that meet the current national or ministerial standards.
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 delays in 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 sanitation projects shall have technical quality appraisal documents or product certificates that meet the current standards issued by the state or the ministry; their product names, models, specifications and national quality standards shall be indicated. Code, date of manufacture, manufacturer’s name and location, factory product inspection certificate or code.
Contraindication 2: The necessary quality inspection is not carried out as required before the valve is installed.
Consequences: The valve switch is not flexible during the operation of the system, the shutdown is not strict and the phenomenon of water leakage (steam) occurs, causing 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 shall be checked by 10% of each batch (same brand, same specification, same model) and not less than one. For closed-circuit valves installed on the main pipe, the strength and tightness tests shall be made one by one. The test strength of the valve strength and tightness shall be in accordance with the “Code for Acceptance of Construction Quality of Building Water Supply and Drainage and Heating Engineering” (GB 50242-2002).
Taboo 3: 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 50 mm; the dry water and the riser of the hot water heating adopt a shut-off valve; and the fire pump suction pipe adopts a butterfly valve.
Consequences: Affect the normal opening and closing of the valve and adjust the resistance and pressure. Even when the system is running, the valve is damaged and forced to repair.
Measures: Familiar with the application range of various types of 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 requirements of construction specifications: the water supply pipe diameter is less than or equal to 50mm should be used as a shut-off valve; when the pipe diameter is greater than 50mm, the gate valve should be used. The hot water heating dry and vertical control valves shall adopt gate valves, and the fire pump suction pipes shall not adopt butterfly valves.
Contraindication 4: The valve installation method is incorrect. For example, the shut-off valve or check valve water (steam) flow direction is opposite to the sign, the valve stem is installed downward, the horizontally mounted check valve is installed vertically, the open gate valve or the butterfly valve handle has no opening and closing space, and the valve stem of the concealed valve Not facing the inspection door.
Consequences: The valve is out of order, the switch is difficult to overhaul, and the valve stem is facing down, which often causes water leakage.
Measures: Strictly install according to the valve installation instructions. The open gate valve stays at the stem opening height. The butterfly valve fully considers the handle rotation space. The various valve stems cannot be lower than the horizontal position, and can not be down. The concealed valve should not only be provided with an inspection door that meets the opening and closing requirements of the valve, but also the valve stem should face the inspection door.
Contraindication 5: Common valve flanges for butterfly valve flanges.
Consequences: The size of the butterfly valve flange and the ordinary valve flange are different. Some flanges have a small inner diameter, and the butterfly valve has a large valve flap, which causes the valve to be broken or hard to open and the valve to be damaged.
Action: The flange must be machined to the actual size of the butterfly valve flange.
Taboo 6: There are no reserved holes and embedded parts in the construction of the building structure, or the reserved holes are small in size and the embedded parts are not marked.
Consequences: During the construction of the heating and sanitation project, the building structure is cut and even the stressed steel bars are cut, which affects the safety performance of the building.
Measures: Conscientiously familiar with the construction drawings of the heating and sanitation project, and actively and conscientiously cooperate with the construction of the structural structure to reserve the holes and embedded parts according to the needs of the installation of the pipeline and the supporting hangers, with specific reference to the design requirements and construction specifications.
Taboo 7: When the pipe is welded, the wrong port of the pipe after the counter is not on a center line, no gap is left in the mouth, and the thick wall pipe does not shovel the groove. The width and height of the weld do not meet the construction specifications.
Consequences: The misalignment of the pipe does not directly affect the quality of the weld and the quality of the look and feel in a centerline. There is no gap in the mouth, and the thick-walled pipe does not shovel the groove. If the width and height of the weld do not meet the requirements, the welding cannot meet the strength requirement.
Measures: After welding the pipe to the mouth, the pipe can not be staggered. It should be on a center line, the gap should be reserved for the mouth, and the thick wall pipe should be shovel. The width and height of the weld should be welded according to the specifications.
Taboo 8: The pipe is directly buried in the frozen soil and the untreated loose soil. The spacing and position of the pipe butt are improper, even in the form of dry brick.
Consequences: Due to the unstable support of the pipeline, the pipeline was damaged during the tamping process, resulting in rework and repair.
Measures: Pipes should not be buried in frozen soil and untreated loose soil. The distance between the piers should meet the requirements of construction specifications, and the support pads should be firm, especially at the pipe joints, and should not be subjected to shearing forces. Brick piers should be built with cement mortar to ensure completeness and firmness.
Contraindications 9: The expansion bolts of the fixed pipe supports are inferior in material. The hole diameter of the installation expansion bolts is too large or the expansion bolts are installed on brick walls or even light walls.
Consequences: The pipe support is loose and the pipe is deformed or even falls off.
Measures: The expansion bolts must be selected as qualified products. If necessary, samples should be tested for inspection. The diameter of the installation expansion bolts should not be larger than the outer diameter of the expansion bolts by 2 mm. The expansion bolts are applied to the concrete structure.
Contraindications 10: The flanges and gaskets of the pipe connections are not strong enough, and the connecting bolts are short or have a small diameter. Heat pipes use rubber mats, cold water pipes use asbestos mats, and double-layer mats or beveled mats with flanged inserts protruding into the tube.
Consequences: The flange connection is not tight, even damaged, and leakage occurs. The flange gasket protrudes into the tube and increases the resistance to water flow.
Measures: Flanges and gaskets for pipes must meet the pressure requirements for piping design. Rubber asbestos mats should be used for the flange gaskets of heating and hot water supply pipes; rubber gaskets should be used for the flange gaskets of water supply and drainage pipes. The gasket of the flange shall not protrude into the pipe, and the outer circle to the flange bolt hole is suitable. No inclined mat or several gaskets shall be placed in the middle of the flange. The bolt diameter of the connecting flange should be less than 2mm than the flange diameter. The length of the bolt stem protruding nut should be 1/2 of the thickness of the nut.
Contraindications 11: When testing the hydraulic pressure test and tightness test of the pipeline system, only the pressure value and the water level change are observed, and the leakage inspection is insufficient.
Consequences: Leakage occurs after the pipeline system is in operation, affecting 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 leakage.
Taboo 12: Sewage, rainwater, and condensate pipes are concealed without a closed water test.
Consequences: 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. Concealed sewage, rainwater, condensate pipes, etc., buried underground, suspended ceilings, pipes, etc., must be ensured to ensure no leakage.
Contraindications 13: Flushing is not serious before the completion of the piping system, and the flow rate and speed are not up to the pipeline flushing requirements. Even flushing with water pressure test leaks instead of flushing.
Consequences: Water quality does not meet the requirements of pipeline system operation, and often results in reduced or blocked pipe sections.
Action: Flush with the maximum juice flow rate in the system or at a water flow rate of not less than 3 m/s. It should be qualified according to the water color of the discharge port, the transparency and the water color and transparency of the inlet water.
Contraindication 14: The hydrostatic test is carried out at a negative temperature during winter construction.
Consequences: The tube freezes quickly due to the rapid freezing of the tube during the hydrostatic test.
Measures: Try to carry out the water pressure test before the winter application, and blow the water after the pressure test, especially the water in the valve must be cleaned, otherwise the valve will freeze. The project must be carried out at a positive temperature in the room during the hydrostatic test in winter, and the water should be blown off after the test. When the hydrostatic test is not possible, it can be tested with compressed air.

Valve installation must pay attention

1. The open rod valve cannot be laid directly.
To prevent corrosion of the valve stem, it can only be installed in the covered trench. The valve should be installed in the position of operation, inspection, disassembly, maintenance and operation.
2. It is not allowed to throw it when handling the valve to avoid damage and deformation.
When stacked, the carbon steel valve should be separated from the stainless steel valve and the non-ferrous metal valve. When the valve is hoisted, the steel wire rope should be placed at the connection flange between the valve body and the valve cover. Do not lie on the hand wheel or the valve stem to prevent damage to the valve stem and the hand wheel.
3. The valve installation position should not interfere with the disassembly, maintenance and operation of equipment, pipelines and valves themselves.
The installation height should be convenient for operation and maintenance. Generally, the operating handle of the valve should be 1-1.2m from the ground. For valves that operate more, when it is necessary to install more than 1.8m from the operating surface, a fixed operating platform should be provided. When it must be installed above or below the operating surface, the extension rod should be installed or the valve stem should be installed horizontally. Install a handwheel with a transmission or a remote operating device.
The angle of the axis of the valve transmission should not exceed 30°, the joint should be flexible to rotate, easy to use during operation, and the indication is accurate. For valves with thermal displacement, the transmission should have compensation measures.
4. For horizontal pipes, it is best to install the valve vertically upwards or install the valve stem in the upper semicircle, but do not install the valve stem downward.
The valve stem and handwheel on the vertical pipe must be installed in the direction of the operating circuit. When conditions permit, the valve should be installed as concentrated as possible for ease of operation. Valves on towers above 4m above the ground should not be placed outside the platform for ease of installation and operation.
5. For directional valves, the installation direction should be determined according to the flow direction of the pipeline.
If a shut-off valve is installed, the medium should flow from below the pavilion to the top, commonly known as low in and out.
When the cock and gate valve are installed, the medium is allowed 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 automatically opened. In important cases, an arrow is marked on the outside of the valve to indicate the flow direction of the medium.
For swing-type check valves, the rotation pivot of the insert plate should be installed in a horizontal position. For lift check valves, ensure that the centerline of the disc is perpendicular to the horizontal.

6. For valves with special requirements, be familiar with the installation requirements.

If a lever type safety valve and a pressure reducing valve are installed, the center line of the valve disc must be perpendicular to the horizontal plane, and correction must be made when the tilt is found.

7. When installing the union and installing the threaded valve on the pipeline, be sure to install the union near the valve for disassembly.
8. The auxiliary system piping should enter the workshop and a shut-off valve should be provided. When the workshop is overhauled, it can be cut off from the main pipeline. These valves are generally mounted at a high height and should be placed as close as possible to provide a fixed operating platform.
9. Install flanged valves. Make sure that the two flanges end faces 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 better to avoid damage to the valve due to incorrect installation position and uneven force. When tightening the flange bolts, use a symmetrical or crisscross method and gradually tighten them in several times.
10. Before installing the high pressure valve, the product certificate and test record must be reviewed. Most of the high-pressure valves are angle valves. They are often used in series. When starting, the starting force is large. The 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 connection on the pump, heat exchanger, tower and vessel shall not bear the weight of the valve and the pipe. The valve with the nominal diameter dn>80mm shall be provided with a bracket.
12. Lining, spraying and non-metallic materials The door itself has high quality and low strength. In addition to considering the process requirements, it should be arranged as much as possible to facilitate the design of the valve frame. Even a single valve should be attached to the valve frame. When installing heavy-duty valves on horizontal pipes, consider installing brackets on both sides of the valve.
13. Install the threaded valve to ensure that the thread is intact. The packing should be selected according to the working conditions. When the screw is in place, the position of the valve stem should meet the installation requirements. When tightening, you must use a wrench to bite the valve hexagonal body on one end of the pipe to ensure that the valve body is not deformed and damaged. Flanged or threaded valves should be installed in the closed position.
14. The bottom sealing of the welding joint between the welding valve and the pipe should be welded by argon arc welding to ensure that the inside is smooth and smooth, and the valve should not be closed during welding to prevent overheating deformation of the sealing surface. If the sealing material is not resistant to high temperatures, the sealing material should be removed before welding to prevent the high temperature from damaging the sealing material.
15. Valves on side-by-side pipelines shall have a clearance of not less than 100 mm between the handwheels. In order to reduce the spacing of the pipelines, the valves arranged side by side are preferably staggered.
16. The cryogenic valve should be opened and closed as far as possible in the cold state before positioning, requiring flexibility and no jamming.
17. The connection of the safety valve should have elbows (or accessories such as tees) to prevent the fluid from directly impacting the valve. In addition, it is necessary to ensure that the safety valve does not frost during operation, so as to avoid failure during operation.
18. It is strictly forbidden to climb the valve stem as a scaffold when the valve is installed.
19. High temperature valve above 200 °C, because the valve is installed at normal temperature, and after normal use, the temperature rises, the valve bolt is heated and the gap is increased, so it must be tightened again, called “heat tight”, the operator should pay attention to this A job, otherwise it is prone to valve leakage and other events.
20. When the winter is cold, the water valve should be closed for a long time. The water accumulated behind the valve should be removed. After the steam valve stops, the condensate should also be excluded. The bottom of the valve is like a drain switch that can be opened to drain.
21. Non-metallic valves, some are hard and brittle, and some have low strength. When operating, the opening and closing force should not be too large, especially not to make it strong. Also pay attention to the object collision.
22. The flow direction of the shut-off valve should be the same as the arrow marked on the valve body (cannot be reversed), so that the pressure is applied to the cone on the top of the valve when the valve is closed, and the packing is not loaded. However, for valves that are not frequently opened and closed and that need to be strictly guaranteed to be leak-proof in the closed state (such as a heating valve), they can be consciously reversed according to the demand to be closed by the medium pressure.
23. Large-size gate valve (DN200-500MM) and pneumatic regulating valve should be installed vertically to prevent the valve core from being biased to one side due to its own 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 slightly open to avoid crushing the top sealing surface.
24. After all the valves are in place, they should be opened and closed again, and the flexible and non-sticking phenomenon is qualified.
25. After the large-scale air separation tower is barely cold, the flange of the connecting valve is pre-tightened in a cold state to prevent the valve from leaking at a low temperature at a normal temperature.

26. When the new valve is in use, the packing should not be pressed too tightly, so as not to leak, so that the valve stem of the valve is too much pressure, the wear is accelerated, and the opening and closing is laborious.

Common valve installation

Installation of gate valve, globe valve and check valve

The gate valve, also known as the gate valve, is a valve that uses the gate to control the opening and closing. The flow section is adjusted and the pipeline is opened and closed by changing the cross section. Gate valves are mostly used for pipes that are fully or fully closed to fluid media. Gate valve installation generally has no directional requirements, but cannot be flipped.

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The shut-off valve is a valve that uses a valve flap to control opening and closing. The medium flow or the medium passage is adjusted by changing the gap between the valve flap and the valve seat, ie changing the size of the passage section. The flow of the fluid must be observed when installing the shut-off valve.

The principle that must be observed when installing the shut-off valve is that the fluid in the pipeline passes through the valve hole from bottom to top, commonly known as “low-in and high-out”, and is not allowed to be reversed.

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Check valve, also known as check valve and check valve, is a valve that automatically opens and closes under the pressure difference between the front and the back of the valve. Its function is to make the medium flow only in one direction and prevent the medium from flowing backwards. The check valve has a lift type, a swing type and a butterfly clip type according to its structure. The lift check valve is divided into horizontal and vertical. When installing the check valve, attention should also be paid to the flow direction of the medium, which cannot be reversed.

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Pressure reducing valve installation

The pressure reducing valve is a valve that adjusts the inlet pressure to a certain required outlet pressure and relies on the energy of the medium itself to automatically maintain the outlet pressure.

From the point of view of fluid mechanics, the pressure reducing valve is a throttling element whose local resistance can be changed, that is, by changing the throttling area, the flow velocity and the kinetic energy of the fluid are changed, resulting in different pressure losses, thereby achieving the purpose of decompression. Then, relying on the adjustment of the control and regulation system, the fluctuation of the post-valve pressure is balanced with the spring force, so that the post-valve pressure remains constant within a certain error range.

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Pressure reducing valve installation

  1. The vertically installed pressure reducing valve group is generally placed along the wall at a suitable height from the ground; the horizontally installed pressure reducing valve group is generally installed on a permanent operating platform.
  2. The application steel is loaded into the wall outside the two control valves (usually used for the shut-off valve) to form the bracket, and the bypass tube is also stuck on the bracket to level the alignment.
  3. The pressure reducing valve should be installed upright on the horizontal pipe, and should not be inclined. The arrow on the valve body should point to the flow direction of the medium and should not be reversed.
  4. Both sides should be equipped with a shut-off valve and high and low pressure gauges to observe the pressure changes before and after the valve. The diameter of the pipe after the pressure reducing valve should be larger than the diameter of the inlet pipe before the valve 2#-3#, and the bypass pipe is installed for maintenance.
  5. The pressure equalizing pipe of the membrane type pressure reducing valve should be connected to the low pressure pipe. For low pressure pipelines, safety valves should be installed to ensure safe operation of the system.
  6. When used for steam decompression, set the drain pipe. For piping systems that require a high degree of purification, a filter is placed in front of the pressure reducing valve.
  7. After the installation of the pressure reducing valve group is completed, the pressure reducing valve and the safety valve shall be pressure tested, flushed and adjusted according to the design requirements, and the adjusted mark shall be made.
  8. When flushing the pressure reducing valve, close the pressure reducing valve inlet valve and open the flushing valve for flushing.

Steam trap installation

The basic function of the steam trap is to discharge the condensate, air and carbon dioxide gas in the steam system as quickly as possible; at the same time, to minimize the automatic leakage of steam. There are many types of traps, each with different properties.

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According to the working principle of the trap, it can be converted into the following three types:

  • Mechanical type: Actions based on changes in the level of condensate in the steam trap, including:
  • Float type: The float is a closed hollow sphere.
  • Open-up float type: The float is a bucket type with an open upward.
  • Open down float type: The float is a bucket type with an open downward.
  • Thermostatic type: Acts on changes in liquid temperature, including:
  • Bimetal: The sensitive component is a bimetal.
  • Steam pressure type: The sensitive component is a bellows or ink cartridge, and the inside is filled with a volatile liquid.
  • Thermodynamic type: Acts upon changes in the thermodynamic properties of the liquid.
  • Disc type: Due to the different flow rates of liquid and gas under the same pressure, the different dynamic and static pressures generated drive the disc valve.
  • Pulse type: Since the condensed water of different temperatures passes through the two-pole series orifice plate, different pressures are formed between the two-pole orifice plate to drive the valve flap to move.

Steam trap installation

  1. A shut-off valve (stop valve) should be installed before and after. A filter should be installed between the trap and the front shut-off valve to prevent dirt in the condensate from clogging the trap.
  2. An inspection tube should be set between the trap and the rear shut-off valve to check whether the trap is working normally. If the inspection tube is opened for a large amount of steam, the trap is broken and needs to be repaired.
  3. The bypass pipe is provided to discharge a large amount of condensed water at the time of starting, and to reduce the displacement load of the steam trap.
  4. When the trap is used to remove the condensate from the hot equipment, it should be installed in the lower part of the heat equipment, so that the water pipe is vertically returned to the steam trap to prevent water from being stored in the heat equipment.
  5. The installation location should be as close as possible to the drainage point. If the distance is too far, air or steam will accumulate in the elongated pipe in front of the trap.
  6. Hydrophobic issues should be considered when the steam mains pipeline is too long.

Safety valve installation

The safety valve is a special valve in which the opening and closing member is in a normally closed state under the action of an external force. When the pressure of the medium in the equipment or the pipeline rises above a specified value, the medium is prevented from exceeding the specified value by discharging the medium outside the system. .

Safety valves are automatic valves, mainly used in boilers, pressure vessels and pipelines. The control pressure does not exceed the specified value, which plays an important role in protecting personal safety and equipment operation. Note The safety valve must be pressure tested before it can be used.

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  1. The product must be carefully inspected before installation to verify whether there is a certificate of conformity and product specifications to clarify the pressure at the factory.
  2. Safety valves should be placed as close as possible to the platform for inspection and maintenance.
  3. The safety valve should be installed vertically, and the medium should flow out from the bottom to the top, and check the verticality of the stem.
  4. Under normal circumstances, the shut-off valve cannot be installed before and after the safety valve to ensure safety and reliability.
  5. Safety valve pressure relief: When the medium is liquid, it is generally discharged into the pipeline or closed system; when the medium is gas, it is generally discharged to the outdoor atmosphere;
  6. 6. Oil and gas medium can generally be discharged into the atmosphere. The outlet of the safety valve venting pipe should be 3m higher than the highest structure around it, but the following conditions should be arranged in a closed system to ensure safety.
  7. The diameter of the population pipeline should be at least equal to the inlet diameter of the valve; the diameter of the discharge pipe should not be smaller than the diameter of the outlet of the valve. The discharge pipe should be led to the outside and installed with a bent pipe so that the pipe outlet faces the safety zone.
  8. When the safety valve is installed, when the connection between the safety valve and the equipment and piping is open-hole welding, the diameter of the opening should be the same as the nominal diameter of the safety valve.

Centralized application of steam trap system

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General valve common faults and causes

1. Reasons for the leakage of the stuffing box and maintenance methods

cause of issue

Maintenance method

Filling method is not correct (such as the whole circle is placed)

Correct packing

Stem deformation or corrosion rust

Repair or renewal

Filler aging

Replacement of packing

Improper operation or excessive force

Slow opening and closing, smooth operation

2. Valve stem failure reasons and maintenance methods

cause of issue

Maintenance method

Stem damage, corrosion trip

Replacement valve

Stem bending

When the valve is not easy to open, do not use a long instrument to identify the handwheel. The bent valve stem needs to be changed.

Stem nut tilt

Replace valve or valve

Open-air valve rust

Open-air valves should be strengthened and the handwheel should be rotated regularly.

3. Sealing surface leakage reasons and maintenance methods

cause of issue

Maintenance method

Sealed surface wear, mild corrosion

Regular grinding

Improper closure, poor sealing contact

Slowly, repeatedly opening and closing several times

The stem is bent, the upper and lower sealing faces are not centered

Repair or replacement

Impurities block the valve hole

Open, remove debris, then slowly close, add filter if necessary

The sealing ring is not tightly matched with the valve seat and the valve disc


The valve flap is not firmly connected to the valve stem

Repair or replacement

4. Other faults, causes and maintenance methods


cause of issue

Maintenance method

Gasket leakage

The material of the gasket is not suitable or is affected by the medium in daily use.

Use gaskets or replacement gaskets that are compatible with working conditions

Valve cracking

Excessive force when installing frozen or threaded valves

Insulation and antifreeze, evenly and properly during installation

Hand wheel damage

Heavy objects hit, long rods are opened, inner holes are worn and chamfered

Avoid impact, even force when opening, correct direction, square hole or replace handwheel

Gland fracture

Uneven force when pressing the cover

Symmetrical tightening nut

Broken gate

The wedge gate is not tight due to corrosion, and the top wedge of the double gate is damaged.

Regular grinding and replacement into carbon steel top wedge

Automatic valve common faults and causes

1. Check valve common faults, causes, prevention and repair


cause of issue

Maintenance method

Media backflow

1. Sealing surface damage between valve plug and seat

2 , there is dirt between the valve core and the valve seat

1 , grinding sealing surface

2 , remove dirt

Spool is not open

1. The sealing surface is stuck by scale

2 , the shaft is rusted

1 , remove scale

2 , polishing the rust to make it flexible

Valve flap broken

The medium pressure before and after the valve is in a close-to-balanced “saw-saw” state, which makes the flaps of brittle materials frequently flapped.

Tough material flap

2. Traps common faults, causes, prevention and repair


cause of issue

Maintenance method


1 , steam pressure is too low

2 , steam and condensate did not enter the steam trap

3 , the float type float is too light

4 , the float type stem and the sleeve are stuck

5 , valve hole or channel blockage

6. The thermostatic valve core is broken and the valve hole is blocked.

1 , adjust the steam pressure

2. Check if the steam pipe valve is closed and blocked.

3 , appropriate addition or replacement of the float

4 , repair or replace, making it flexible

5 , remove the clogged debris, install the filter in front of the valve

6 , replace the spool

Exhaust steam

1 , the valve core and seat are worn, leaking steam

2 , the drain hole can not be closed by itself

3 , the buoy type buoy is small in size and cannot float

1 , grinding sealing surface

2 , check for dirt and blockage

3 , properly increase the size of the float

Continuous working temperature drop

1. The displacement is lower than the amount of condensate 2. The amount of condensate in the pipeline increases.

1 , replace the appropriate steam trap

2 , install a steam trap

3. Pressure reducing valve common faults, causes, prevention and maintenance


cause of issue

Maintenance method

Post-valve pressure instability

1. Pulse type is improper selection of valve diameter, large pressure difference between two ends of the medium

2 , the spring type of adjustment spring is not properly selected

1. Replace the appropriate pressure reducing valve

2 , replace the appropriate adjustment spring

Valve does not pass

1. The control channel is blocked by debris.

2 , the rust inside the piston is stuck, can not move down at the highest position

1 , remove debris, valve front filter

2 , repair the piston to make it flexible

Valve straight through

1 , the piston stuck in a certain position

2 , the main valve flap lower spring break

3 , the pulse valve valve handle is stuck at the close position

4. There is dirt stuck or severe corrosion between the main valve flap and the seat sealing surface.

5 , film failure

1. Repair the piston to make it flexible

2 , replace the spring

3 , overhaul, make it flexible

4 , remove dirt, regular grinding sealing surface

5 , replace the film

Post-valve pressure cannot be adjusted

1 , adjusting the spring failure

2 , the cap has a leak, can not maintain pressure

3 , piston, cylinder wear or corrosion

4 , the valve body is filled with condensed water

1 , replace the adjustment spring

2 , timely maintenance, replace the gasket

3 , repair the cylinder, replace the piston ring

4 , loosen the plug, drain the condensate

4. Safety valve common faults, causes, prevention and repair


cause of issue

Maintenance method

Sealing surface leakage

1. Sewage or wear on the sealing surface of the valve plug and seat

2 , the stem center line is not correct

1. Remove dirt or abrasive seals

2 , correct the alignment stem center line

Exceeding working pressure does not open

1. The lever is stuck or the pin is rusted.

2 , the lever weight is moved

3 , spring-type spring is deformed or failed by heat

4 , the valve core and the valve seat stick

1. Overhaul levers or sales

2 , adjust the weight position

3 , replace the spring

4 , regular exhaust test

Open without working pressure

1. The weight of the lever moves inward

2 , spring-type elastic is not enough

1. Adjust the weight position

2 , tighten or replace the spring

The spool does not close automatically after opening

1. Lever-type lever deflection

2 , spring-type spring bending

3 , the valve core or stem is not correct

1 , maintenance lever

2 , adjust the spring

3 , adjust the valve plug or valve stem

Common valve overhaul

During the installation and use of the valve, due to manufacturing quality and wear, the valve is prone to leakage and tight closure.

1. Gland leak repair

  • (1) Small bonnet leak overhaul
  • (2) Large valve gland leakage overhaul

2. Can’t open or open the air, no water

  • (1) Gate valve
  • (2) Globe valve
  • (3) Valve or pipe blockage

3. Can’t hold or close

  • (1) The door is not tight: it may be due to dirt between the valve seat and the valve core, or the valve seat and the valve core are scratched, so that the valve cannot be closed.
  • (2) Can’t keep it: When the valve is opened, the force is too strong and the head is turned over.

Source: China Valves Manufacturer – Yaang Pipe Industry Co., Limited (www.steeljrv.com)

(Yaang Pipe Industry is a leading manufacturer and supplier of nickel alloy and stainless steel products, including Super Duplex Stainless Steel Flanges, Stainless Steel Flanges, Stainless Steel Pipe Fittings, Stainless Steel Pipe. Yaang products are widely used in Shipbuilding, Nuclear power, Marine engineering, Petroleum, Chemical, Mining, Sewage treatment, Natural gas and Pressure vessels and other industries.)

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