Duct system installation

1. General Provisions

a. This chapter applies to the inspection and acceptance of the installation quality of metal and non-metal duct systems in ventilation and air conditioning projects.

b. After the duct system is installed, it must be inspected for tightness, and it can only be delivered to the next process after passing the inspection. The tightness inspection of the duct system is mainly based on the main and trunk pipes. Under the premise that the processing technology is guaranteed, the low-pressure duct system can be inspected by the light leakage method.

c. When the duct system hanger and bracket are fixed by expansion anchoring methods such as expansion swing bolts, they must comply with the provisions of the corresponding technical documents.

This section only makes corresponding provisions for the general construction content of the duct system installation. Such as the inspection and testing of the tightness of the duct system, the provisions for the anchoring of duct hangers and bracket expansion bolts, etc. The tightness inspection of the duct system in the project is a relatively difficult task. 

(Figure 1: Pipe system installation)

2. Main control items

a. When the air duct passes through the fireproof and explosion-proof wall or floor that needs to be closed, a pre-buried pipe or protective sleeve should be installed, and the steel plate thickness should not be less than 1.6mm. Between the air duct and the protective sleeve, non-flammable and harmless flexible materials should be used to seal.

Inspection quantity: 20% by quantity, not less than 1 system.

Inspection method: measurement, observation and inspection.

b. The installation of air ducts must comply with the following regulations:

• It is strictly forbidden to cross other pipelines in the air duct.

• The air duct system that transports flammable and explosive gases or is installed in a flammable and explosive environment should have good grounding, and must be tight when passing through the living area or other auxiliary production rooms. No interface shall be set;

• The fixed cable of the outdoor riser is strictly prohibited to be pulled on the lightning rod or lightning rod network.

Inspection quantity: 20% of the quantity shall be randomly inspected, and no less than 1 system shall be inspected.

Inspection method: hand wrench, measurement, observation inspection.

c. For air ducts with air delivery temperature higher than 80"C, protective measures shall be taken according to the design regulations.

Inspection quantity: 20% of the quantity shall be randomly inspected, and no less than 1 system shall be inspected.

Inspection method: observation inspection.

(Figure 2: Installation of air duct assembly)

d. The installation of air duct components must comply with the following regulations

• The installation of various air duct components and operating mechanisms shall ensure their normal use functions and be easy to operate:

• When installing the oblique plug-in plate air valve, the valve plate must be pulled up; when installed horizontally, the valve plate should also be inserted in the direction of air flow;

• The installation direction of the check valve and automatic exhaust valve should be correct.

Inspection quantity: 20% of the quantity shall be randomly inspected, and no less than 5 pieces shall be inspected.

Inspection method: measurement, observation inspection, action test.

Description: This article stipulates the main control items that should be accepted for the installation of general components in the air duct system. 

e. The installation direction and position of fire dampers and smoke exhaust valves (ports) should be correct. The fire dampers on both sides of the fire partition wall should not be greater than 200mm from the surface. 

Inspection quantity: 20% of the quantity shall be randomly inspected, and shall not be less than 5 pieces. 

Inspection method: measurement, observation inspection, action test. 

Note: The installation direction and position of fire dampers and smoke exhaust valves will affect the normal function of the valves, so they must be correct. The farther the fire dampers on both sides of the firewall are from the wall, the higher the fire resistance requirements for the through-wall pipes, and the worse the function of the valves, so the provisions have made provisions for this. 

(Figure 3: Smoke exhaust valve)

f. The installation of the air duct of the purification Air conditioning system shall also comply with the following provisions: 

• The air duct, static pressure box and other components must be wiped clean to ensure that there is no oil and dust. When the construction is paused or completed, the port should be sealed; 

• Flange gaskets should be made of non-dust-producing, non-aging, and strong and elastic materials with a thickness of 5-8mm. Latex sponges should not be used. Flange gaskets should be spliced as little as possible, and straight seam joints are not allowed. It is strictly forbidden to apply paint on the surface of the gasket: 

• The joints between the air duct and the ceiling, partitions and other enclosure structures of the clean room should be tight.

Inspection quantity: 20% of the quantity should be randomly inspected, and no less than 1 system should be inspected. 

Inspection method: Observation and wiping with a cloth. 

Explanation: This article stipulates the main control items that should be accepted for the installation of the purification air duct system. 

g. The installation of the centralized vacuum system should comply with the following provisions: The radius of curvature of the vacuum system bend should not be less than 4 times the pipe diameter, the inner wall of the bend should be smooth, and wrinkled bends should not be used. The angle of the tee of the vacuum system should not be greater than 45°; two oblique tees should be used for production. 

(Figure 4: Installation of air ducts for purification air conditioning system)

Inspection quantity: 20% of the quantity should be randomly inspected, and no less than 2 pieces should be inspected. 

Inspection method: measurement and observation inspection .

Note: This article stipulates the main control items that should be accepted for the installation of the vacuum dust collection duct system.

h. After the duct system is installed, it should be inspected for tightness according to the system type, and the air leakage should meet the requirements. The tightness test of the duct system should comply with the following provisions: The tightness test of the low-pressure system duct should be carried out by random inspection, with a sampling rate of 5%, and not less than 1 system. Under the premise that the processing technology is guaranteed, the light leakage method is used for detection. If the test fails, the air leakage test should be carried out according to the prescribed sampling rate.

The tightness test of the medium-pressure system duct should be carried out after the light leakage method test is qualified, and the system air leakage test should be carried out by random inspection, with a sampling rate of 20%, and not less than 1 system.

The tightness test of the high-pressure system duct is to conduct air leakage test for all.

(Figure 5: Air leakage test)

The inspected systems of the system duct tightness test should be qualified in all cases, and then they are deemed to have passed; if there are unqualified ones, they should be doubled for random inspection until all are qualified. Tightness test of air ducts in purification air conditioning systems.

Inspection quantity: as specified in the article.

Inspection method: conduct tightness test in accordance with the provisions of this specification.

Explanation: This article mandates a tightness test for air duct systems after installation, aligning with international standards for ventilation and air conditioning engineering. Conducting the leakage test can be challenging, requiring specialized instruments and proper sealing of system openings, as well as coordination with the project's construction progress.

To address the specific needs of air duct systems in China, this specification categorizes the tightness inspection into three levels, detailing the number and methods for random checks. High-pressure duct systems require thorough inspections due to their significant impact on system operation, while medium-pressure systems, which include low-level purification and humidity control, have lower leakage tolerance. For these systems, extensive manpower for leakage measurement is discouraged; instead, strict supervision during construction is recommended.

During light leakage detection, the absence of numerous leaks indicates stable quality, allowing for the acceptance of the system without further testing. Conversely, significant light leaks suggest processing quality issues, necessitating an air leakage test. For purification air conditioning systems, excessive leakage affects cleanliness targets, so acceptance should follow high-pressure system criteria.

i. When installing the manual closed valve, the direction of the arrow marked on the valve must be consistent with the direction of the shock wave.

Inspection quantity: full inspection.

Inspection method: observation and verification.

Instructions: The manual closed valve is set to prevent the harm of high-pressure shock waves to the human body, and the installation direction must be correct.

(Figure 6: Leakage test of air duct system)

3. General items

a. The installation of air ducts shall comply with the following provisions:

• Before installing the air duct, internal and external debris should be removed, and cleaning and protection work should be done well;

• The location, elevation and direction of the air duct installation should meet the design requirements. The configuration of the on-site air duct interface shall not reduce its effective cross-section;

• The swing bolts of the connecting flanges should be tightened evenly, and their female straightness should be on the same side:

• The connection of the air duct interface should be tight and firm. The gasket material of the air duct flange should meet the requirements of the system function, and the thickness should not be less than 3mm. The gasket should not protrude into the pipe.

• The installation of the flexible short pipe should be moderately tight and without obvious distortion:

• The length of the flexible or non-flexible duct should not exceed 2m, and there should be no dead bends or concave

The connection interface between the air duct and the brick or concrete air duct should be inserted along the air flow direction, and sealing measures should be taken. A rainproof device should be installed at the place where the air duct passes through the roof. The contact between the stainless steel plate and aluminum plate air duct and the carbon steel bracket should be isolated or anti-corrosion insulation measures.

(Figure 7: Air duct cleaning and maintenance)

Inspection quantity: 10% of the quantity shall be randomly inspected, and no less than 1 system shall be inspected.

Inspection method: measurement and observation inspection.

Explanation: This article stipulates the basic quality acceptance requirements for the installation of the duct system. For example, the duct interface, return bend or reducer installed on site, due to improper configuration and excessive reduction of the cross section, often affects the normal operation of the system, among which the interface connecting the fan and the air conditioning equipment is the most seriously affected.

b. The installation of air ducts without flange connection should also comply with the following regulations:

• The connection of the air duct should be complete and without defects, the surface should be flat, and there should be no obvious distortion:

• The gaps around the socket-type air duct should be consistent, without obvious bending or wrinkles; the sealant applied inside should be complete, and the sealing tape applied outside should be firmly attached, complete and without defects;

• For the connection of thin steel plate flange air ducts, the interval between elastic inserts, spring clips or fastening bolts should not be greater than 150mm, and they should be evenly distributed without looseness;

• For rectangular air ducts connected by inserts, the board surface after connection should be flat and without obvious bending.

Inspection quantity: 10% of the quantity should be randomly inspected, and no less than 1 system.

Inspection method: measurement and observation inspection.

Explanation: This article stipulates the basic quality acceptance requirements for the installation of air ducts without flange connection by category.

c. The connection of the air duct should be straight and not twisted. For the horizontal installation of exposed air ducts, the allowable deviation of the horizontality is 3/1000, and the total deviation should not be greater than 20mm. The exposed air duct is installed vertically, and the allowable deviation of verticality is 2/1000, and the total deviation should not be greater than 20mm. 

The position of the concealed air duct should be correct and without obvious deviation. 

The air duct of the dust removal system should be laid vertically or tilted, and the angle with the horizontal should be greater than or equal to 45°. 

The small slope and horizontal pipe should be as short as possible. For air ducts containing condensate or other liquids, the slope should meet the design requirements, and a drainage device should be installed at the lowest point. 

(Figure 8: Dust removal system air duct)

Inspection quantity: 10% by quantity, but not less than 1 system. 

Inspection method: measurement, observation and inspection.

Explanation: This article stipulates the acceptance requirements for the position, horizontality, verticality, etc. of the installation of the system air duct. There is no quantitative provision for the horizontality and verticality of the concealed air duct, only requiring "the position should be correct and without obvious deviation". This is not to lower the standard, but to start from the actual construction. If the concealed air duct is also required to be horizontal and vertical, it is of little practical significance. Moreover, in a narrow space, various pipes cross vertically, which is objectively difficult to do.

d. The installation of duct supports and hangers shall comply with the following provisions:

When the duct is installed horizontally, the diameter or long side dimension is less than or equal to 400mm, and the spacing should not be greater than 4m; greater than 400mm, it should not be greater than 3m. The spacing between supports and hangers for spiral ducts can be extended to 5m and 3.75m respectively; for ducts with thin steel plate flanges, the spacing between supports and hangers should not be greater than 3m.

When the duct is installed vertically, the spacing should not be greater than 4m, and a single straight pipe should have at least 2 fixing points.

For special ducts with a diameter or side length over 2500 mm, supports and hangers must follow design regulations. Hangers should not be placed at vents, valves, inspection doors, or control mechanisms, with a minimum distance of 200 mm from vents or pipes.

(Figure 9: Installation of support brackets for the air duct system)

For horizontal main and trunk ducts longer than 20 m, fixed points must be installed to prevent swinging, with at least one per system. Hanger screw holes should be machined, and hangers must be straight with smooth threads. After installation, all supports and hangers should evenly distribute force without significant deformation.

Adjustable vibration isolation supports and hangers must be set according to design requirements. Clamp bracket corners should be straight, and clamps must securely hold the duct. Circular ducts on brackets need both support and clamps, with consistent arc alignment to the duct's outer diameter.

Inspection quantity: 10% by quantity, not less than 1 system.

Inspection method: measurement and visual inspection.

Explanation: This article stipulates the acceptance requirements for the installation quality of the support and hanger of the air duct system. After the air duct is installed, it should also be adjusted immediately to avoid uneven force on the auxiliary support and hanger or local deformation of the air duct.

e. The installation of non-metallic air ducts shall also comply with the following provisions:

• The two flange end faces of the air duct connection shall be parallel and tight, and galvanized washers shall be added on both sides of the flange bolts:

• The contact area between the support and hanger and the horizontal air duct shall be appropriately increased;

• The straight section continuous length of the rigid polyvinyl chloride air duct is greater than 20m, and the expansion joint shall be set according to the design requirements; the weight of the branch pipe shall not be borne by the main pipe, and the support and hanger must be set by itself:

• The air duct is installed vertically, and the bracket spacing shall not be greater than 3m.

Inspection quantity: 10% of the quantity shall be randomly inspected, and shall not be less than 1 system.

Inspection method: measurement and observation inspection.

f. The installation of composite material air ducts shall also comply with the following provisions:

• The connection of the composite material air duct shall be firm, without holes and cracks. When using plug-in connection, the interface shall be matched and not loose, and the port gap shall not be greater than 5mm;

• When using flange connection, measures should be taken to prevent cold bridges;

• The installation of supports and hangers shall be carried out in accordance with the provisions of product standards.

(Figure 10: Composite material air duct)

Inspection quantity: 10% by quantity, but not less than 1 system.

Inspection method: measurement and observation inspection.

g. The installation of centralized vacuum dust collection system shall comply with the following provisions:

• The slope of the dust collection duct shall be declared as 5/1000, and shall slope towards the vertical pipe or dust collection point;

• The connection between the dust collection nozzle and the duct shall be firm and tight.

Inspection quantity: 20% by quantity, but not less than 5 pieces.

Inspection method: measurement and observation inspection.

Explanation: The provisions stipulate the acceptance requirements for the basic quality of installation of non-metallic, composite materials, and centralized vacuum dust collection duct systems.

h. All kinds of air valves shall be installed in places that are convenient for operation and maintenance. The manual or electric operating devices after installation shall be flexible and reliable, and the valve plate shall be closed tightly.

When the diameter or long side dimension of the fire damper is greater than or equal to 630mm, independent supports and hangers should be provided.

The position of the exhaust valve (exhaust port) and the manual control device (including the embedded sleeve) shall meet the design requirements, and the embedded sleeve shall not be dead or trapped.

(Figure 11: Vacuum dust collection system)

The regulating valve of the suction pipe section of the dust removal system should be installed on the vertical pipe section.

Inspection quantity: 10% of the quantity shall be randomly checked, and shall not be less than 5 pieces.

Inspection method: measurement and observation inspection.

Note: This article stipulates the acceptance requirements for the installation quality of various types of air valves in the air duct system.

i. The hood must be installed firmly, and the junction between the air duct and the roof or wall should not be seawater.

Inspection quantity: 10% of the quantity shall be randomly checked, and shall not be less than 5 pieces.

Inspection method: measurement and observation inspection.

Note: This article stipulates the most basic quality requirements (firm and leak-free) for the installation of hoods in the air duct system.

j. The installation position of the exhaust and suction hoods should be correct, neatly arranged, firm and reliable.

(Figure 12: Duct system hood)

Inspection quantity: 10% of the quantity shall be randomly checked, and shall not be less than 5 pieces.

Inspection method: measurement and observation inspection.

Explanation: This article stipulates the basic quality requirements for the installation of hoods in duct systems.

k.  The connection between the vent and the duct should be tight and firm, close to the decorative surface; the surface should be flat and not deformed, and the adjustment should be flexible and reliable. When installing strip vents, the joints should be naturally connected without obvious gaps. The installation height of the same vents in the same hall or room should be consistent and the arrangement should be neat. For vents installed without ceilings, the installation position and elevation difference should not be greater than 10mm.

The vent is installed horizontally, and the deviation of the horizontality should not be greater than 3/1000.

The vent is installed vertically, and the deviation of the verticality should not be greater than 2/1000.

Inspection quantity: 10% of the quantity shall be randomly inspected, and no less than 1 system or no less than 5 pieces and 2 rooms of vents.

Inspection method: measurement, observation and inspection.

Explanation: This article stipulates the basic quality requirements for the installation of vents in duct systems. The quality of vent installation should be based on the tightness of the connection and the comfort and beauty of the appearance.

(Figure 13: Air outlet of purification air conditioning system)

l. The installation of air outlets in purification air conditioning systems shall also comply with the following provisions:

• The air outlets shall be cleaned before installation, and the joints between the frame and the building, ceiling or wall shall be provided with sealing gaskets or sealants, and there shall be no air leakage:

• The air outlets with high-efficiency filters shall use hanging rods with adjustable heights.

Inspection quantity: 20% shall be randomly inspected by quantity, and the air outlets shall not be less than 1 system or not less than 5 pieces and 2 rooms.

Inspection method: measurement and observation inspection.

Note: The installation of air outlets in purification air conditioning systems has higher requirements, so this article has made additional provisions.