Valves are the most common equipment in chemical enterprises. Installing valves may seem easy, but if not implemented according to relevant technologies, it can lead to safety accidents. Today, I will share some experience and knowledge about valve installation with you.

Taboo 1

Consequence: Due to the rapid freezing inside the pipe during the hydraulic test, the pipe freezes out.

Measures: Try to conduct a water pressure test before winter construction, and after the pressure test, the water should be blown clean, especially the water inside

the valve must be removed completely. Otherwise, the valve may rust slightly and freeze crack severely.

When conducting hydraulic tests in winter, the project must maintain a positive indoor temperature, and the water should be blown clean after the pressure test.

Taboo 2

The pipeline system was not flushed carefully before completion, and the flow and speed did not meet the requirements for pipeline flushing. Even using hydraulic strength testing to release water instead of flushing.

Consequence: If the water quality does not meet the operational requirements of the pipeline system, it often leads to a reduction or blockage of the pipeline cross-section.

Measure: Flush with the maximum set juice flow rate in the system or a water flow rate that should not be less than 3m/s. It should be deemed qualified if the color and transparency of the discharge water are visually consistent with those of the inlet water.

Taboo 3

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

Consequence: May cause water leakage and result in user losses.

Measures: The closed water test work should be strictly inspected and accepted in accordance with the specifications. Concealed sewage, rainwater, condensate pipes, etc. buried underground, in suspended ceilings, between pipes, etc., should be ensured to prevent seepage and leakage.

Taboo 4

During the hydraulic strength test and leak test of the pipeline system, only observing the pressure value and water level changes is not enough for leakage inspection.

Consequence: Leakage occurs after the pipeline system operates, affecting normal use.

Measures: When conducting tests on the pipeline system in accordance with design requirements and construction specifications, in addition to recording pressure or water level changes within the specified time, it is particularly important to carefully check for any leakage issues.

Taboos 5

Butterfly valve flanges are ordinary valve flanges.

Consequence: The size of the butterfly valve flange is different from that of a regular valve flange. Some flanges have a small inner diameter, while the butterfly valve disc is large, causing the valve to be unable to open or hard to open, resulting in valve damage.

Measure: The flange plate should be machined according to the actual size of the butterfly valve flange.

Taboo 6

There are no reserved holes or embedded parts in the construction of building structures, or the reserved hole size is too small and the embedded parts are not marked.

Consequence: During the construction of heating and sanitation projects, the building structure is chiseled and even the load-bearing steel bars are cut, affecting the safety performance of the building.

Measures: Carefully familiarize yourself with the construction drawings of the heating and sanitation engineering, and actively cooperate with the construction of reserved holes and embedded parts in the building structure according to the needs of pipeline and support and hanger installation. Please refer to the design requirements and construction specifications for specific details.

Taboos 7

When welding pipelines, the misalignment of the pipes after alignment is not on the same centerline, and there is no gap between the alignment. Thick walled pipes do not have bevels, and the width and height of the weld seam do not meet the requirements of construction specifications.

Consequence: The misalignment of the pipes not on the same centerline directly affects the welding quality and visual quality. When there is no gap between the joints, thick walled pipes are not chamfered, and the width and height of the weld seam do not meet the requirements, the welding cannot meet the strength requirements.

Measures: After welding the pipeline, the pipeline should not be misaligned and should be on the same centerline; Gaps should be left for alignment; Thick walled pipes need to be beveled. In addition, the width and height of the weld seam should be welded according to the specification requirements.

Taboo 8

The pipeline is directly buried on frozen soil and untreated loose soil, and the spacing and position of pipeline piers are improper, even using dry bricks.

Consequence: Due to unstable support, the pipeline suffered damage during the backfilling and compaction process, resulting in rework and repair.

Measures: The pipeline shall not be buried on frozen soil or untreated loose soil, and the spacing between support piers shall comply with the construction specifications. The support pads shall be firm, especially at the pipeline interface, and shall not bear shear forces. Brick piers should be built with cement mortar to ensure completeness and firmness.

Taboo 9

The material of the expansion bolts used to fix the pipeline support is poor, and the hole diameter for installing the expansion bolts is too large or the expansion bolts are installed on brick walls or even lightweight walls.

Consequence: The pipeline support is loose, causing deformation or even detachment of the pipeline.

Measures: Qualified products must be selected for expansion bolts, and if necessary, samples should be taken for testing and inspection. The hole diameter for installing expansion bolts should not be greater than 2mm of the outer diameter of the expansion bolts. Expansion bolts should be used on concrete structures.

Taboos 10

The flange plate and gasket used for pipeline connection are not strong enough, and the connecting bolts are short or have a small diameter. Heating pipelines use rubber pads, cold water pipelines use double-layer pads or inclined pads, and flange gaskets protrude into the pipes.

Consequence: The flange connection is not tight, or even damaged, resulting in leakage. The flange gasket protruding into the pipe will increase water flow resistance.

Measures: The flange and gasket used in the pipeline must meet the requirements of the pipeline design working pressure.

Rubber asbestos pads should be used as flange gaskets for heating and hot water supply pipelines; Rubber gaskets should be used for the flange gaskets of water supply and drainage pipelines.

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

Taboos 11

The valve installation method is incorrect.

For example, for globe or check valves, the water (steam) flow direction is opposite to the mark, and the valve stem is installed downwards. For horizontally installed check valves, they are installed vertically. For rising stem gate or butterfly valve handles, there is no open or close space, and for concealed valves, the valve stem is not facing the inspection door.

Consequence: Valve failure, difficult maintenance of switches, and downward valve stem often cause water leakage.

Measures: Strictly follow the valve installation manual for installation, leave sufficient stem extension and opening height for rising stem gate valves, fully consider the handle rotation space for butterfly valves, and all valve stems should not be lower than the horizontal position, let alone downward. Concealed valves should not only have inspection doors that meet the opening and closing requirements of the valve, but also have the valve stem facing towards the inspection door.

Taboos 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; When the diameter of the water supply branch pipe is less than or equal to 50mm, a gate valve is used; The dry and vertical pipes for hot water heating use shut-off valves; The suction pipe of the fire water pump adopts a butterfly valve.

Consequence: It affects the normal opening and closing of the valve, as well as the adjustment of resistance, pressure, and other functions. Even causing valve damage and forced repair during system operation.

Measures: Familiarize yourself with the application range of various valves, and select the specifications and models of valves according to the design requirements. The nominal pressure of the valve should meet the requirements of the system test pressure. According to construction specifications, cut-off valves should be used for water supply branch pipes with a diameter less than or equal to 50mm; When the pipe diameter is greater than 50mm, a gate valve should be used. The dry and vertical control valves for hot water heating should use gate valves, and the suction pipe of the fire pump should not use butterfly valves.

Taboos 13

Failure to conduct necessary quality inspections as required before valve installation.

Consequence: During system operation, the valve switch is not flexible, the valve is not tightly closed, and water (steam) leakage occurs, resulting in rework and repair, and even affecting normal water supply (steam).

Measures: Before installing the valve, pressure strength and tightness tests should be conducted. The test should be conducted by sampling 10% of each batch (of the same brand, specification, and model), and not less than one. For closed circuit valves installed on the main pipeline that have a cutting effect, strength and tightness tests should be conducted one by one. The strength and tightness test pressure of the valve should comply with the provisions of the "Code for Acceptance of Construction Quality of Building Water Supply, Drainage and Heating Engineering" (GB 50242-2002).

Taboos 14

The main materials, equipment, and products used in construction lack technical quality appraisal documents or product certificates that comply with current national or ministerial standards.

Consequence: The engineering quality is unqualified, there are potential accidents, and it cannot be delivered and used on time, and must be reworked and repaired; Causing delays in the construction period and an increase in labor and material inputs.

Measures: The main materials, equipment, and products used in the water supply and drainage and heating and sanitation engineering should have technical quality appraisal documents or product qualification certificates that comply with the current national or ministerial standards; The product name, model, specification, national quality standard code, factory date, manufacturer name and location, and factory product inspection certificate or code should be indicated.

Taboos 15

Valve inversion

Consequence: Valves such as check valves, throttle valves, pressure reducing valves, and check valves all have directional characteristics. If installed upside down, the throttle valve will affect its effectiveness and lifespan; The pressure reducing valve is not working at all, and the check valve can even cause danger.

Measures: For general valves, there are directional signs on the valve body; If not, it should be correctly identified based on the working principle of the valve. The valve chamber of the shut-off valve is asymmetric from left to right, and the fluid should pass through the valve port from bottom to top. This way, 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, making it easy for maintenance. This is why the shut-off valve cannot be reversed. Do not install the gate valve upside down (i.e. with the handwheel facing downwards), otherwise the medium will remain in the valve cover space for a long time, which is easy to corrode the valve stem and is prohibited by certain process requirements. It is extremely inconvenient to replace the packing at the same time. Rising stem gate valves should not be installed underground, otherwise the exposed stem will corrode due to moisture. When installing a lift check valve, ensure that the valve disc is vertical for flexible lifting and lowering. When installing a swing check valve, ensure that its pin shaft is horizontal for flexible swing. The pressure reducing valve should be installed vertically on a horizontal pipeline, without tilting in any direction.

Taboos 16

Manual valve opening and closing with excessive force

Consequences: ranging from valve damage to safety accidents

Measure: The manual valve, with its handwheel or handle, is designed according to ordinary manual labor, taking into account the strength of the sealing surface and the necessary closing force. Therefore, it is not possible to use a long lever or a long wrench to move the board. Some people are accustomed to using a wrench and should be strictly careful not to use too much force, otherwise it may damage the sealing surface or break the handwheel or handle. When opening and closing the valve, the force should be steady and not impact. Some components of high-pressure valves with impact opening and closing have considered that this impact force cannot be equal to that of ordinary valves. For steam valves, prior to opening, they should be preheated and condensed water should be drained. When opening, they should be opened as slowly as possible to avoid water hammer. After the valve is fully opened, the handwheel should be turned back a little to tighten the threads tightly to avoid loosening and damage. For rising stem valves, it is important to remember the stem position when fully open and fully closed to avoid hitting the top dead center when fully open. And facilitate the inspection of whether it is normal when fully closed. If the valve stem falls off or there are large debris embedded between the valve core seals, the position of the valve stem will change when fully closed. When the pipeline is first used, there is a lot of internal dirt. The valve can be slightly opened, and the high-speed flow of the medium can be used to flush it away. Then, it can be gently closed (not quickly closed or forcefully closed to prevent residual impurities from damaging the sealing surface), and then opened again. Repeat this process multiple times to flush out the dirt before putting it into normal operation. Normally open valves may have dirt sticking to their sealing surfaces. When closing, the above method should also be used to flush them clean and then officially close them tightly. If the handwheel or handle is damaged or lost, it should be immediately equipped and cannot be replaced by a flexible wrench to avoid damaging the valve stem and causing accidents during production due to poor opening and closing. Some media cool down after the valve is closed, causing the valve to contract. The operator should close it again at an appropriate time to ensure that there are no gaps on the sealing surface. Otherwise, the media can flow through the gaps at high speed and easily erode the sealing surface. When operating, if it is found that the operation is too laborious, the reason should be analyzed. If the packing is too tight, it can be relaxed appropriately. If the valve stem is tilted, personnel should be notified for repair. Some valves, when in a closed state, experience thermal expansion of the closing part, causing difficulty in opening; If it is necessary to open at this time, the valve cover thread can be loosened by half a turn to one turn to eliminate the stress on the valve stem, and then the handwheel can be turned.

Taboos 17

Improper installation of valves in high-temperature environments

Consequence: Causing a leakage accident

Measures: High temperature valves above 200 ℃ must be tightened again due to being installed at room temperature. After normal use, the temperature increases, the bolts expand due to heat, and the gap increases. This is called "hot tightening". Operators should pay attention to this work, otherwise leakage may occur.

Taboos 18

Delayed drainage in cold weather

Measures: When the weather is cold and the water valve is closed for a long time, the accumulated water behind the valve should be drained. After the steam valve stops, the condensate should also be discharged. The bottom of the valve is like a plug, which can be opened for drainage.

Taboos 19

Non metallic valves with excessive opening and closing force

Measures: Some non-metallic valves are hard and brittle, while others have lower strength. When operating, the opening and closing force should not be too large, especially not with strong force. Also, pay attention to avoiding collisions with objects.

Taboos 20

The packing of the new valve is pressed too tightly

Measures: When using a new valve, do not press the packing too tightly to prevent leakage, in order to avoid excessive pressure on the valve stem, accelerated wear, and difficult opening and closing. The quality of valve installation directly affects its use, so it is necessary to carefully pay attention to the direction and position of the valve, valve construction operations, valve protection facilities, bypasses and instruments, and valve packing replacement.

Taboos 21

Installation location without operating space

Measures: The installation position of the valve must be convenient for operation; Even if installation is temporarily difficult, it is important to consider the long-term work of the operators. It is best to align the valve handwheel with the chest (usually 1.2 meters from the operating floor), so that opening and closing the valve is more effortless. The handwheel of the floor mounted valve should be facing upwards and not tilted to avoid awkward operation. The valve of the wall machine against the equipment should also leave room for operators to stand. It is necessary to avoid operating in the sky, especially with acid, alkali, toxic media, etc., otherwise it is very unsafe.

Taboos 22

Valves made of impact brittle materials

Measures: Care must be taken during installation and construction to avoid hitting valves made of brittle materials. Before installation, the valve should be inspected to verify its specifications and model, and to identify any damage, especially for the valve stem. We need to rotate it a few more times to see if it is skewed, as the valve stem is most likely to be knocked out during transportation. Also, remove any debris from the valve. When lifting the valve, the rope should not be tied to the handwheel or valve stem to avoid damaging these components. It should be tied to the flange. The pipeline connected to the valve must be cleaned thoroughly. Compressed air can be used to blow away iron oxide chips, mud and sand, welding slag, and other debris. These impurities not only easily scratch the sealing surface of the valve, but also block the small valve with large particles (such as welding slag), making it ineffective. When installing a screw valve, the sealing filler (hemp, lead oil, or PTFE raw material tape) should be wrapped around the pipe thread and not get into the valve to avoid accumulation in the valve and affecting the flow of the medium. When installing flange valves, it is important to tighten the bolts symmetrically and evenly. The valve flange and pipe flange must be parallel and have a reasonable gap to avoid excessive pressure or even cracking on the valve. For brittle materials and valves with low strength, special attention should be paid. Valves that need to be welded to the pipe should be spot welded first, then the closing part should be fully opened, and then welded tightly.

Taboos 23

The valve has not undergone insulation and cold insulation measures

Measures: Some valves also require external protective facilities, which are insulation and cold insulation. Sometimes, heat tracing steam pipelines are added inside the insulation layer. What type of valve should be insulated or cooled depends on production requirements. In principle, if the temperature of the medium inside the valve decreases too much, it will affect production efficiency or freeze the valve, so insulation or even heat tracing is necessary; When the valve is exposed, which is detrimental to production or causes adverse phenomena such as frost formation, cold insulation is necessary. Insulation materials include asbestos, slag wool, glass wool, perlite, diatomaceous earth, vermiculite, etc; Cold insulation materials include cork, perlite, foam, plastic, etc.

Taboos 24

The drain valve is not equipped with a bypass

Measures: Some valves, in addition to necessary protective facilities, also need to have bypasses and instruments. A bypass has been installed for easy maintenance of the drain valve. Other valves also have bypass installed. Whether to install a bypass depends on the condition, importance, and production requirements of the valve.

Taboos 25

Failure to regularly replace packing

Measures: For inventory valves, some of the packing is no longer suitable, and some do not match the medium used, which requires replacement of the packing.

The valve faces thousands of different media, and the packing box is always filled with ordinary packing. However, when using it, the packing must be adapted to the media.

When replacing the packing, press it in circle by circle. The appropriate joint for each circle is 45 degrees, and the joints between circles should be staggered by 180 degrees. The height of the packing should consider the space for the gland to continue to be compressed. At present, the lower part of the gland should be pressed into the packing chamber at an appropriate depth, which 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 seams between the circles are staggered by 120 degrees.

In addition to the above fillers, rubber O-rings (natural rubber resistant to weak alkalis below 60 degrees Celsius, nitrile rubber resistant to oil products below 80 degrees Celsius, and fluororubber resistant to various corrosive media below 150 degrees Celsius) can also be used according to specific circumstances. Three piece 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) can also be used as forming fillers. Wrapping a layer of polytetrafluoroethylene raw material tape outside the ordinary asbestos packing can improve the sealing effect and reduce electrochemical corrosion of the valve stem.