Dry goods | Twenty-five taboos on valve installation, how much do you know?

Issuing time:2019-12-05 09:05

Valves are the most common equipment in chemical companies. It seems easy to install valves, but if they are not implemented in accordance with relevant technologies, safety accidents will occur. Today, I will share with you some experience about valve installation.

Taboo 1

Hydraulic tests are performed at negative temperatures during winter construction.

Consequence: The tube freezes quickly due to the rapid freezing in the tube during the hydrostatic test.

Measures: Try to perform a hydraulic 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 rust, and the valve will freeze and crack.

The project must be carried out at a positive indoor temperature during the hydrostatic test in winter, and the water should be blown off after the test.

Taboo 2

The piping system was not flushed carefully before completion, and the flow and speed did not meet the requirements for piping flushing. Even hydraulic pressure test leaks instead of flushing.

Consequences: The water quality does not meet the requirements of the pipeline system, and often causes the pipeline section to decrease or block.

Measures: Use the maximum juice flow in the system or the water flow speed should not be less than 3m / s for flushing. It shall be qualified that the color and transparency of the water at the outlet and the color and transparency of the water at the inlet are consistent with visual inspection.

Taboo 3

Sewage, rainwater, and condensate pipes are concealed without a closed water test.

Consequence: May cause water leakage and loss to users.

Measures: The closed-water test work shall be strictly checked and accepted in accordance with the specifications. Concealed sewage, rainwater, and condensate pipes, such as those buried underground, inside the ceiling, and between pipes, must be leak-proof.

Taboo 4

In the hydraulic system strength test and tightness test of the piping system, only the pressure value and water level change are observed, and the leakage inspection is not enough.

Consequence: Leakage occurs after the pipeline system runs, which affects 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.

Taboo 5

Butterfly valve flanges use common valve flanges.

Consequences: The size of the flange of the butterfly valve is different from that of the ordinary valve. Some flanges have a small internal diameter, and the butterfly valve has a large flap, which can cause the valve to fail to open or hard to open, causing damage to the valve.

Measures: The flange should be processed according to the actual size of the butterfly valve flange.

Taboo 6

There are no holes or embedded parts reserved 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, picking up the building structure, or even cutting off the reinforced steel bars, affects the safety performance of the building.

Measures: Familiarize yourself with the construction drawings of the heating and sanitation project, and actively cooperate with the construction structure to reserve holes and embedded parts according to the requirements of the installation of pipes and supports and hangers, and refer to the design requirements and construction specifications.

Taboo 7

When the pipe is welded, the pipe misalignment is not on a center line after the counterpart, there is no gap in the counterpart, the thick-walled pipe does not shovel the bevel, and the width and height of the weld do not meet the requirements of the construction code.

Consequence: The misalignment of the tube is not directly on the center line, which directly affects the welding quality and the quality of the look and feel. There is no gap at the mouth, the bevel of thick-walled pipes is not shovel, and the width and height of the welds do not meet the requirements of strength when the welding does not meet the requirements.

Measures: After welding the pipe counterparts, the pipes must not be staggered and must be on a center line; gaps should be left at the counterparts; thick-walled pipes should be shoveled. In addition, the width and height of the weld shall be welded in accordance with the requirements of the code.

Taboo 8

The pipeline is directly buried in frozen soil and untreated loose soil. The distance and location of the support pier of the pipeline are improper, even in the form of dry code bricks.

Consequence: Due to the unstable support of the pipeline, the pipeline was damaged during the compaction of the backfill soil, resulting in rework and repair.

Measures: The pipeline must not be buried in frozen soil and untreated loose soil. The distance between the pier should meet the requirements of the construction code, and the support pads should be firm, especially at the interface of the pipeline. The brick pier should be built with cement mortar to ensure completeness and firmness.

Taboo 9

The expansion bolts used to fix the pipe bracket are of inferior material. The hole diameter for installing the expansion bolts is too large or the expansion bolts are installed on brick walls or even light walls.

Consequence: The pipe support is loose, the pipe is deformed, or even falls off.

Measures: Qualified products must be selected for the expansion bolts. If necessary, samples should be tested and tested. The diameter of the expansion bolts should not be greater than 2mm.

Taboo 10

The flange and gasket of the pipe connection are not strong enough, and the connecting bolts are short or thin in diameter. Rubber pipes are used for thermal pipes, double-layered or beveled gaskets are used for cold water pipes, and flange gaskets protrude into the pipes.

Consequence: The flange connection is not tight, even damaged, and leakage occurs. Flange gaskets protrude into the tube and increase water resistance.

Measures: The flanges and gaskets for pipelines must meet the requirements of the design working pressure of the pipelines.

Rubber asbestos gaskets should be used as flange gaskets for heating and hot water supply pipes; rubber gaskets should be used as flange gaskets for water supply and drainage pipes.

The gasket of the flange must not protrude into the pipe, and its outer circle is appropriate to the flange bolt hole. No flange pad or several gaskets should be placed in the middle of the flange. The diameter of the bolt connecting the flange should be less than 2mm than the diameter of the flange. The length of the protruding nut of the bolt rod should be 1/2 of the thickness of the nut.

Taboo 11

Incorrect valve installation method.

For example, the water (steam) flow direction of the stop valve or check valve is opposite to the mark, the valve stem is installed downwards, and the horizontally installed check valve is installed vertically. Do not face the inspection door.

Consequence: The valve fails, the switch is difficult to repair and repair, and the valve stem often causes water leakage.

Measures: Install strictly in accordance with the valve installation instructions. The open stem gate valve should be left with the valve stem extended to open height. The butterfly valve fully considers the turning space of the handle. The various valve stems cannot be lower than the horizontal position, nor can they be downward. The concealed valve should not only be provided with an inspection door that meets the needs of valve opening and closing, but also the valve stem should face the inspection door.

Taboo 12

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 branch pipe of the water supply when the diameter is less than or equal to 50mm; the stop valve for hot and dry pipes is used; and the butterfly valve is used for the suction pipe of the fire pump.

Consequences: Affects the normal opening and closing of the valve and adjusts resistance, pressure and other functions. It even caused the valve to be repaired during system operation.

Measures: Familiar with the application scope of various valves, and choose the specifications and models of the 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 code: a stop valve should be used for the pipe diameter of the water supply branch pipe less than or equal to 50mm; a gate valve should be used when the pipe diameter is greater than 50mm. Gate valves for hot water heating, dry, and vertical control valves should be used, and butterfly valves should not be used for fire pump suction pipes.

Taboo 13

Before the valve is installed, the necessary quality inspection is not performed as required.

Consequence: The valve switch is not flexible during the operation of the system, the closure is not strict, and the phenomenon of water leakage (steam) occurs, which causes rework repair and even affects normal water supply (steam).

Measures: Before the valve is installed, the pressure strength and tightness test should be performed. The test shall be carried out by random inspection of 10% and not less than one in each batch (same brand, same specification, same model).

For the closed-circuit valve installed on the main pipe to cut off, the strength and tightness test should be performed 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).

Taboo 14

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, it cannot be delivered and used on schedule, and it must be reworked for repairs; causing delays in the construction period and increased labor and material inputs.

Measures: The main materials, equipment and products used in water supply, drainage and sanitation engineering should have technical quality appraisal documents or product certifications that meet the current standards issued by the country or the ministry; their product names, models, specifications, and national quality standards should be indicated Code, date of manufacture, name and location of the manufacturer, inspection certificate or code of the manufactured product.

Taboo 15

Valve flip

Consequence: Check valve, throttle valve, pressure reducing valve, check valve and other valves are directional. If it is installed upside down, the throttle will affect the use effect and life; the pressure reducing valve will not work at all, the check valve It can even be dangerous.

Measures: General valves have directional signs on the valve body; in case of no, they should be correctly identified according to the working principle of the valve. The valve cavity of the globe valve is asymmetrical left and right. The fluid must pass through the valve port from bottom to top, so the fluid resistance is small (determined by the shape), and the opening is labor-saving (due to the pressure of the medium upwards). . This is why the shut-off valve is not reversible.

Do not install the gate valve upside down (that is, the handwheel is downward), otherwise the medium will remain in the bonnet space for a long time, it is easy to corrode the valve stem, and it is contraindicated for certain process requirements. It is extremely inconvenient to change the packing at the same time.

Open-stem gate valves should not be installed underground, otherwise the exposed valve stem will be corroded due to humidity.

The lifting check valve should be installed vertically to ensure its flexibility.

For swing check valve, the pin should be level during installation to allow flexible swing.

The pressure reducing valve should be installed upright on a horizontal pipe, and it should not be inclined in all directions.

Taboo 16

Manual valve opens and closes with excessive force

Consequences: the valve may be damaged in a small way, and a safety accident may be caused in a serious way

Measures: The manual valve, its handwheel or handle, is designed according to ordinary manpower, taking into account the strength of the sealing surface and the necessary closing force. Therefore, you cannot use a long lever or a long wrench to move. Some people are accustomed to using the wrench. Care should be taken not to apply too much force or force, otherwise the sealing surface may be damaged, or the handwheel or handle may be broken. Open and close the valve, the force should be stable and not impact. Some parts of high-pressure valves that have been opened and closed due to shocks have considered such impact forces and ordinary valves cannot be equal. For the steam valve, before opening, it should be heated in advance and the condensed water should be eliminated. When opening, it should be slowed down as much as possible to avoid water hammer. When the valve is fully open, the handwheel should be turned upside down a little to tighten the threads tightly to prevent loosening damage. For open-stem valves, remember the position of the stem when fully open and fully closed to avoid hitting the top dead center when fully open. And easy to check whether it is normal when fully closed. If the valve sheds, or if large debris is embedded between the valve core seals, the valve stem position will change when fully closed. When the pipeline is used for the first time, there is a lot of internal dirt, you can slightly open the valve, use the high-speed flow of the medium to flush it away, and then gently close it (cannot be closed quickly or violently to prevent the residual impurities from pinching the sealing surface) Turn it on again, repeat this many times, rinse the dirt, and then put it back into normal work. Normally open valve, dirt may be stuck on the sealing surface. When it is closed, it must be flushed clean by the above method, and then closed formally. If the handwheel or handle is damaged or lost, it should be equipped immediately. It can not be replaced by a flexible wrench, so as not to damage the four sides of the valve stem, opening and closing failure, and an accident in production. For some media, after the valve is closed, it will cool down and cause the valve to shrink. The operator should close it again at an appropriate time so that there are no crevices on the sealing surface. Otherwise, the medium flows through the crevices at high speed and it is easy to erode the sealing surface. . During operation, if it is found that the operation is too laborious, the cause should be analyzed. If the packing is too tight, it can be properly relaxed. If the valve stem is skewed, the personnel should be notified to repair it. Some valves, in the closed state, the closing member is thermally expanded, which makes it difficult to open; if it must be opened at this time, the valve cover screw can be loosened half a turn to one turn to eliminate the valve stem stress, and then move the handwheel.

Taboo 17

Improper valve installation in high temperature environments

Consequences: a spill

Measures: Because the high temperature valve above 200 ℃ is at normal temperature during installation, after normal use, the temperature rises, the bolts are heated and expand, and the gap is increased. Therefore, they must be tightened again, called "heat tight". The operator must pay attention to this work , Otherwise it is easy to leak.

Taboo 18

Cold weather does not drain in time

Measures: When the weather is cold, the water valve is closed for a long time, and the water behind the valve should be drained. Condensate should also be drained after the steam valve is stopped. The bottom of the valve is like a wire plug, which can be opened to drain water.

Taboo 19

Non-metallic valve with too much opening and closing force

Measures: Some non-metallic valves are hard and brittle, and some have low strength. During operation, the opening and closing force should not be too large, especially not to be vigorous. Also pay attention to avoid collision of objects.

Taboo 20

New valve packing pressure is too tight

Measures: When using the new valve, do not press the packing too tightly, so as not to leak, so as not to pressure the valve stem too much, accelerate wear and tear, and open and close effort. The quality of valve installation directly affects the use, so careful attention must be paid to the direction and location of the valve, valve construction work, valve protection facilities, bypass and instrumentation, valve packing replacement.

Taboo 21

No operating space at installation location

Measures: The valve installation position must be convenient for operation; even if the installation is temporarily difficult, the long-term work of the operator must be considered. It is best to align the valve handwheel with the chest (usually 1.2 meters away from the operating floor). In this way, it is easier to open and close the valve. The handwheel of the floor valve should be facing up and not tilted to avoid awkward operation. The valve of the wall-to-wall machine and the equipment should also allow 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.

Taboo 22

Valve made of impact brittle material

Measures: Care must be taken during installation and construction. Avoid hitting valves made of brittle materials. Before installation, check the valve, check the specifications and models, and check for damage, especially for the valve stem. You need to turn it a few times to see if it is skewed, because it is the easiest to bump the valve stem during transportation. Also remove debris from the valve. When the valve is being lifted, do not tie the rope to the handwheel or valve stem to avoid damaging these parts. It should be tied to the flange. The pipeline to which the valve is connected must be cleaned. Compressed air can be used to remove iron oxide filings, mud, sand, welding slag and other debris. These debris, not only easily scratch the sealing surface of the valve, among which large particles (such as welding slag), can also block the small valve and make it invalid. When installing a screw valve, the sealing packing (linen plus lead oil or Teflon raw material tape) should be wrapped in the thread of the pipe, so as not to get into the valve, so as to prevent the valve from accumulating and affecting the flow of the medium. When installing flange valves, pay attention to tighten the bolts symmetrically and evenly. The valve flange and the pipe flange must be parallel with a reasonable gap to prevent the valve from generating excessive pressure or even cracking. Special attention should be paid to brittle materials and low strength valves. Valves to be welded to the pipe should be spot welded, then the closing parts should be fully opened, and then welded to death.

Taboo 23

The valve is not insulated or cooled.

Measures: Some valves also need external protection facilities. This is insulation and cooling. Sometimes heat tracing steam lines are added to the insulation. What kind of valve should be insulated or kept cold depends on the production requirements. In principle, where the temperature of the medium in the valve is too low, it will affect production efficiency or freeze the valve, it will need heat preservation, or even heat tracing; where the valve is exposed, it is unfavorable to production or causes frost formation and other undesirable phenomena, it needs to keep cold. Insulation materials include asbestos, slag wool, glass wool, perlite, diatomaceous earth, vermiculite, etc .; cold insulation materials include cork, perlite, foam, plastic, etc.

Taboo 24

Trap without bypass installed

Measures: Some valves, in addition to necessary protection facilities, also have bypasses and meters. A bypass is installed for easy maintenance of the trap. Other valves are also equipped with bypass. Whether to install a bypass depends on the condition, importance and production requirements of the valve.

Taboo 25

Packing is not changed regularly

Measures: Some valves are not suitable for storage valves, and some do not match the use of the medium. This requires replacement of the packing.

The valve faces thousands of different types of media. The packing box is always filled with ordinary packing, but when used, the packing must be adapted to the medium.

When changing the packing, turn around

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公司地址:天津市河西区美年广场4-801                                            联系邮箱:frank.pan@kxc-metal.com                                                                   联系电话:18622652376