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What are the fourteen taboos and solutions for valve installation?

November 06,2023

Taboo 1

Conduct water pressure tests at negative temperatures during winter construction.

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 test, blow the water clean, especially the water inside the valve must be removed completely, otherwise the valve will freeze and crack.

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. When hydraulic testing is not possible, compressed air can be used for testing.

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., must ensure no seepage or 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.

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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. The alignment should leave gaps, and thick walled pipes should be chamfered. In addition, the width and height of the weld seam should be welded according to the specifications.

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. Rubber gaskets are used for heating pipelines, asbestos gaskets are used for cold water pipelines, and double-layer or inclined gaskets are used, with flange gaskets protruding 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).

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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.


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