How To Make And Install Air Duct (Project Solution)?

1. Project overview

The project is located on Modao Island, Zhongshan City, with a total construction area of 34580 square meters.

Air duct installation works include: smoke exhaust system, positive pressure air supply system, exhaust system, fresh air and air conditioning system.

2. Preparation basis

● Schematic design engineering drawings

● Unified standard for quality acceptance of Building Engineering (GB50300-2001)

● Code for acceptance of construction quality of ventilation and air conditioning engineering (GB50243-2002)

● Standard for safety inspection of building construction (JGJ59-99)

3. Ventilation and air conditioning construction scheme

In modern installation engineering, with the progress of science and technology, new materials and new processes emerge one after another in the process of making and installing air-conditioning air duct, and the TDF flange air duct is one of them.

The air duct adopts full-automatic production line and combines the world’s advanced numerical control and optical fiber information technology.

In addition to producing galvanized rectangular air duct, it can also produce various special-shaped air duct accessories such as elbow, tee and cross.

It plays a more and more important role in installation engineering.

1. Process characteristics of air duct:

1) Production line mechanization

The high degree of automation greatly improves the manufacturing efficiency and the manufacturing accuracy of the air duct, and reduces the project cost.

2) The air duct forms its own flange to reduce the weight of the air duct.

Compared with the traditional angle iron flange, it saves the flange section steel and connecting bolts and reduces the material loss.

3) The air duct has good sealing, significantly reduces air leakage, saves energy and reduces the operation cost of the main engine.

4) The air duct has many advantages, such as high strength, no solder joint, good corrosion resistance, tight connection, low air leakage rate, beautiful and tidy appearance, and no damage to the zinc coating.

5) Fast production and installation, reduce labor intensity, provide labor efficiency and meet the needs of the project.

2. Air duct manufacturing equipment

No. Equipment list Spec. Qty Function
1 Automatic  production line AML-III 2 sets Blanking, beading and folding of air duct materials
2 TDF flange forming machine T-12 2 sets Forming of special flange for TDF air duct
3 Automatic plasma blanking machine PCM-1250*3100 1 set Automatic blanking of air duct fittings
4 Air duct seaming machine LC-12DR 1 set Automatic joint and undercut of air duct
5 Air duct folding machine WE67Y-100/3200 2 sets Special folding for TDF flange
6 Spiral duct production line Φ80~Φ1500 Article 1 Production of circular spiral duct
7 Steel round pipe forming machine W11-4/1300 1 set Professional production of wall casing and civil air defense circular duct
8 Steel round flange machine JY-50 1 set Production of circular flange of air duct
9 Plasma cutting machine LGK-100 2 sets Shaped air outlet opening
10 Resistance spot welder DNJ-25 1 set Professional production of static pressure box and deflector
11 Argon arc welding machine WSM-200 1 set Professional wall casing, civil air defense circular pipe production, etc
12 Professional automatic argon arc welding machine NBC-250 1 set Special equipment for making stainless steel ventilation pipe
13 Punch 35T 1 set Produce air duct accessory
14 Round elbow machine SBWT-700 1 set Manufacture of round air duct fittings
15 Shearing machine Q11*2000 1 set Air duct blanking
16 Other supporting special electric machines and tools 1 batch 1 batch /

3 . Main construction scheme

3.1 plate selection

The thickness of the steel plate used for making air duct shall be in strict accordance with the provisions of national standard GB50243-2002.

Thickness of steel plate of air duct and accessories (mm)

Duct diameter or long side size

Circular duct

Rectangular duct

Air duct of dust removal system

Medium and low voltage system

High voltage system
































By design


By design

By design


A. The steel plate thickness of spiral air duct can be reduced by 10% ~ 15%

B. The steel plate thickness of the air duct of the smoke exhaust system can be determined according to the high-pressure system

C. It is not applicable to the embedded pipe of underground civil air defense and firewall

3.2 manufacturing process of air duct

3.2.1 draw the blanking processing sketch of the air duct

According to the construction drawings and the actual situation on site (the installation elevation and direction of the air duct and the coordination with other disciplines), the processing sketch shall be drawn on site according to the system served by the air duct and numbered according to the system.

3.2.2.  production process

Input the draft size of air duct processing into the computer → enter the galvanized plate and straighten it in the production line → beading → cut the plate by the shear → lockformer → machine-made TFD flange forming machine → bending by the folder → quality inspection

Installation diagram of TDF flange air duct

Installation diagram of TDF flange air duct

3.2.3 fabrication of TDF air duct

a. When making the air duct, the blanking drawing input into the computer must be correct, the plate surface should be kept flat, and the undercut seam should be tight. The width of the undercut joint shall be uniform, and the longitudinal joint shall be staggered for a certain distance, so as not to reduce the quality of the air duct.

b. Mechanical processing is mainly used for blanking, lockforming and folding of duct in the project, supplemented by manual operation.

c. The galvanized steel plate is connected by lockformer, the locking of air duct plate adopts single lock, and the four corner of rectangular air duct adopts combined angle (corner mold) lock.

d. The side length of the smoke control and exhaust air duct of the project is large.

In order to avoid the deformation of the air duct section and reduce the noise caused by the vibration of the pipe wall during the system operation, the air duct needs to be reinforced.

During the construction, the following methods are mainly adopted for reinforcement in combination with the site conditions.

e. Press the stiffener on the surface of the air duct plate;

According to the size of galvanized steel plate, the length of TDF air duct section is made into a section of 1160mm;

f. The air duct is processed and formed (cage pipe), and the corner mold is installed at the four corners of the TDF flange.

Note that the diagonal length of the air duct is consistent.

g. Sealant selection shall meet the following requirements:

It has good adhesion performance and can be applied to various materials.

The sticky skin is moderate. (the bonding effect of sealing materials with too high viscosity is not very good, but the effect is better when using materials with lower viscosity)

It can withstand the air pressure and various properties of gas in the receiving pipe to ensure water tightness and air tightness.

h. The air ducts that fully meet the requirements shall be numbered in sections according to the processing sketch, and the pipe orifice shall be blocked with plastic film for installation.

Schematic diagram of flange edge folding by mechanical folder

Semi finished products when the common flange air duct is not assembled

Semi finished products when the TDF air duct is not assembled

Photo of TDF flange air duct

Photo of TDF flange air duct

3.3 installation of galvanized steel sheet air duct

a. The installation sequence of air duct is generally from main pipe to branch pipe, and the vertical air duct is generally installed in sections from bottom to top. 

The installation methods of each part are as follows:

Installation method of air duct


Air duct height < 3.5m

Air duct height < 3.5m

Horizontal duct

Main air duct

Integral installation

Sectional installation

Install tools

Mobile platform, chain fall

Elevator, mobile platform, scaffold, chain fall

Branch air duct

Sectional installation

Sectional installation

Install tools

Mobile platform and pulley

Elevator, mobile platform, scaffold, chain fall

Vertical air duct

Pulley, chain block, high stool

Pulley, chain block and scaffold

b. Flange connection

The gasket for flange connection shall be made of materials that do not leak air, produce dust, have good elasticity, are not easy to aging and have a certain strength.

The sealing material used for the connection of the smoke exhaust air duct must meet the class A material required by fire acceptance.

The flange gasket shall reduce the joints, and the joints must be connected in trapezoid or tenon shape.

The gasket shall be clean, shall not protrude into the air duct, and shall be firmly bonded with adhesive.

During flange connection, pad the gasket, align the flange, put on the bolts at the four corners of the TDF flange, and put on the nuts to tighten.

The middle section between the four corner bolts of the flange shall be fixed with hook bars or bolt clamps (those with side length less than 1000mm shall be reinforced with hook bars, and those with side length greater than 1000mm shall be fixed with special bolt clamps).

The thickness of the bolt clamp body must be 1.6mm higher than that required by fire acceptance, i.e. more than 2.0.

The connected air duct shall be subject to the flanges at both ends, and the cable shall be used to check whether the air duct connection is straight.

Bolts and nuts for flange connection shall be galvanized parts.

During connection, the nut shall be on the same side of the flange, and the length of the bolt exposed to the nut shall be appropriate and consistent.

c. The overall installation of the air duct means that the air duct is extended to 1-20m on the ground, and then the air duct is opened to the installation height and fixed by chain fall.

Select the lifting point and hang the chain fall according to the actual situation on site.

The number of lifting points shall ensure that the air duct is not deformed during lifting.

When lifting, when the air duct is 200-300mm above the ground, stop lifting, carefully check whether the lifting point, rope and rope buckle are firm, and whether the center of gravity of the air duct is correct.

After confirmation, continue lifting.

Lift the air duct to the predetermined position, connect all pallets and suspenders, stabilize the air duct, untie the rope buckle and remove the chain fall.

d. The air duct is installed in sections.

The air duct sections can be pulled to the scaffold with ropes, and then lifted to the support to install the flange section by section.

e. Before hoisting, the inner and outer walls of the air duct must be wiped clean.

When the construction is completed or stopped, the port must be sealed with plastic film to prevent secondary pollution.

f. After the air duct is installed, the adjustment screw on the suspender or the cushion on the bracket can be used for leveling and alignment.

g. After the air duct is adjusted, the fixed support shall be set according to the design requirements to prevent the air duct from shaking.

3.3.1 Installation of air duct and components

A. Preliminary conditions for air duct installation

a. After the civil works meet certain conditions, the installation of air ducts and components can be carried out.

The installation of exposed air duct shall be carried out after the civil construction of the installation part of ventilation duct or the completion of main works, floor and painting;

If civil engineering and other works are carried out after the installation of the ventilation duct, the ventilation duct may be damaged.

b. In the process of civil construction, special personnel shall be assigned to closely cooperate with the civil construction according to the schedule of civil construction, and do a good job in the reservation of holes and the laying of embedded parts.

Installed TDF flange air duct

Installed TDF flange air duct

Duct during installation

Duct during installation Installation of flexible air duct

The flexible air duct is made of metal aggregate and coated fiber fabric (or metal film) wall materials, which are processed and formed by winding, and the metal aggregate is used as the supporting frame to make the air duct have the necessary strength;

Coated fabric (or metal film) with its high flexibility makes the air duct flexible, telescopic, shock-absorbing, silencing and other characteristics.

At present, it is commonly used in the connection between the main Phoenix pipe and the air outlet or static pressure box.

Installation process requirements

a. Sagging amount of horizontal flexible air duct h ≤ D / S

b. Minimum bending radius of flexible air duct R ≥ D

c. Connecting pipe length of flexible air duct and hard pipe L ≥ D

The flexible air duct support adopts flat steel (made into a circular ring) to be suspended under the floor or other components:

D(mm)Lifting ring materialSupport spacingNumber of supports

D. The support ring shall contact at least half of the circumferential surface of the air duct, and the effective inner diameter of the air duct shall not be reduced.

E. Lifting rings shall be set at the flexible air duct close to the hard pipe interface to make the connection between the flexible air duct and the hard pipe interface more firm and avoid wrinkles of the air duct.

When in use, the flexible air duct shall be opened as far as possible to avoid unnecessary wind pressure loss.

During installation, after the installation of the main air duct and static pressure box, select the optimal flexible air duct direction according to the actual situation on site, determine the position of the hard pipe interface, and then open on the main air duct to install the hard pipe interface. Installation of air outlet and components

1) Air valve installation

a. The air duct system of the project mainly includes multi-leaf regulating valve, butterfly valve, fire and smoke control valve and other air valves.

Before installation, check whether the frame structure is firm, and the adjustment, braking, positioning and other devices shall be accurate and flexible.

b. Punch holes on the flange of the air valve according to the screw hole size of the air duct flange.

c. The installation of the air valve is the same as that of the air duct.

During installation, just align the flange of the valve with the flange on the air duct or equipment, add a sealing gasket and tighten the screws to make it firmly and tightly connected.

d. Pay attention to the installation position of the air valve to make the control position of the valve easy to operate.

e. During installation, pay attention to the air flow direction of the air valve, do not install it reversely, and install it according to the direction marked on the air valve shell.

f. The fire damper is the safety device of the ventilation system. It is necessary to ensure that it plays the role of closing and shutdown in case of fire.

The fire damper can be divided into horizontal, vertical, left and right types.

The ordering and installation shall be carried out according to the design requirements.

The fire damper can be divided into horizontal, vertical, left and right types.

The ordering and installation shall be carried out according to the design requirements to prevent mistakes.

In order to prevent the fusible sheet of the fire damper from falling off, the fusible sheet shall be installed after the system installation and before the system test run.

g. In order to facilitate the replacement and inspection of the fusible sheet of the fire damper, an inspection door shall also be set on the air duct section close to the fire damper according to the design.

2) Air outlet installation

a. The installation of various air outlets shall be horizontal, straight and flat.

The exposed part shall be parallel to the indoor line, and the air outlet surface of various diffusers shall be parallel to the ceiling.

b. After the tuyere arrives, check the specification and size of the tuyere according to the drawing, stack it separately according to the system and mark it well to avoid mistakes during installation.

c. Carefully check the air outlet before installation, especially the air outlet with adjustment and rotation parts.

Check whether the moving parts are light and flexible, whether the blades are straight, and whether the shutter can be opened and closed freely.

d. After the installation of the tuyere, the movable parts of the tuyere shall also be checked again to prevent deformation during handling and installation and affect the adjustment function of the tuyere. Finished product protection

a. During the whole construction process, the raw materials, construction finished products and semi-finished products shall be actively protected.

The ventilation works mainly pay attention to the following points:

b. The finished products of air ducts shall be stacked neatly according to the system number, and shall be handled and handled with care to prevent damage.

c. There are many cross operations and additional works.

It is strictly prohibited to use the installed air duct as the support, hanger and bracket.

It is not allowed to weld or hang other supports and hangers on the air duct flange and air duct supports and hangers, let alone stand on the air duct. Key points for construction

a. Joint review of drawings before engineering: understand the design intention and clarify the operation position of each discipline

b. Drawing processing drawings:

Through drawings and field measurements, it is clear whether the pipeline direction and elevation of each system are in contradiction with the ventilation pipeline and the specifications and dimensions of air ducts and components.

After considering various factors, draw the air duct processing sketch.

c. Prepare material demand plan:

Provide accurate information on various material specifications.

d. During the structural construction, the air duct opening shall be reserved, and the size shall be sufficient for the air duct to pass through.

e. Material preparation:

Make incoming inspection.

f. Installation of air duct support.

Coordinate, elevation and support spacing shall be confirmed.

The firmness of the support is the key to ensuring the safe operation of the air duct.

g. Installation of air duct: the flange is tightly connected.

h. Light leakage test of air duct: conducted in dark environment. The light leakage rate shall not be greater than the specification requirements.

J. Installation of air outlet: the position is correct, horizontal and vertical.

3.4 Detection of light and air leakage of air duct

A. Light leakage detection of air duct

Light leakage detection is a method to detect the tightness of the air duct of the system by using the strong penetration of light to the small hole.

① Standard for light leakage detection

When the light leakage method is used to detect the tightness of the system, the air duct of the low-pressure system is qualified with no more than 2 light leakage points per 10m joint and no more than 16 joints per 100m;

For the medium pressure air duct, it is qualified if the light leakage point is no more than 1 for every 10m joint and no more than 8 for every 100m joint.

② Specific operation method of light leakage detection

The safety light source with certain intensity, not less than 100W low-voltage lighting lamp with protective cover, shall be used as the light source for light leakage detection.

When detecting the light leakage of the air duct of the system, the light source can be placed inside or outside the air duct, but the opposite side should be in a dark environment.

The detection light source moves slowly along the detected part and joint, and observes on the other side.

When light is found to be emitted, it means that obvious air leakage is found and recorded.

The air duct of the system adopts the method of segmented detection and summary analysis.

On the basis of strict installation quality management, the detection of system air duct is mainly based on main pipe and main pipe.

If slit-shaped light leakage is found in light leakage detection, it shall be treated according to different light leakage parts.

If it is at the flange, tighten the bolts and replace the sealing gasket; In case of undercut, seal with sealant.

If the light leakage of the undercut joint is serious, the air duct of this section shall be fabricated and installed again, and the light leakage test shall be conducted again.

If the light leakage test is unqualified, the air leakage test shall be conducted according to the specified sampling rate.

B. Air leakage test

The measuring instrument used for the air leakage test of the air duct must be qualified and within the validity period.

At the same time, the measuring element in accordance with the current national standard flow measurement throttling device shall be used to set up the test device for measuring the air leakage per unit area of the air duct.

The inspection standard of allowable air leakage per unit area of air duct is shown in the following table:

Allowable air leakage per unit area of air duct (m3 / h·m2)

Working pressure (PA)200300400500600800100012001500
Allowable air leakage of low pressure system3314.305.196.00     
Allowable air leakage of medium pressure system    2.252.713.143.534.08

The air leakage detection of the air duct of the medium pressure system must be carried out on the basis of passing the light leakage detection.

① Preparations before the test:

Take down the branch pipe connecting the air duct to be measured to the air outlet, and seal the opening with a blind plate.

② Test method:

Use the test fan to blow into the air duct to make the static pressure in the air duct rise to the required test pressure (Pa) and stabilize the pressure.

At this time, the air inlet in the air duct is equal to the air leakage.

The air volume is measured by the orifice plate set between the fan and the air duct.

 ③ Test device:

Test Fan: it is a variable air volume centrifugal fan.

The maximum air volume of the fan is 1600m3 / h and the maximum air pressure is 2400Pa.

Connecting pipe: Ф 100mm

Orifice plate: when the air leakage is ≥ 130 m3 / h, the orifice plate constant C = 0.697 and the aperture = 0.0707m

When the air leakage is less than 130 m3 / h, the orifice constant C = 0.603 and the aperture = 0.0316m

Inclined micro manometer: measure the pressure difference of orifice plate 0 ~ 2000Pa

The pressure difference of orifice tube is 0 ~ 2000Pa.

Test steps

A) air leakage sound test:

This test is conducted before air leakage measurement.

During the test, remove the branch pipe, seal the opening with blind plate and tape, and connect the hose of the test device to the measured air pipe.

Close the air inlet baffle and start the fan.

Gradually open the air inlet baffle until the static pressure in the air duct rises and remains at the test pressure.

Pay attention to the sound of air leakage at all joints and holes of the air duct, mark each air leakage point and repair it.

B) air leakage test:

This test is carried out after the air leakage sound point is sealed.

During the test, first start the fan, and then gradually open the air inlet baffle until the static pressure in the air duct rises and remains at the test.

Read the pressure difference on both sides of the orifice plate and calculate the air leakage of the measured air duct according to the following formula:

The air leakage is calculated according to the following formula:



  • Q – air leakage, (m3 / h)
  • ε— Air velocity expansion coefficient
  • ρ— Air density (kg / m3)
  • An – opening area of orifice plate (m2)
  • α— Orifice discharge coefficient
  • △ p – orifice differential pressure (Pa)

4. Quality requirements

1. The air duct joint shall be tight, the width shall be uniform, and there shall be no defects such as holes, half bite and expansion crack.

2. The flange connection of air duct shall be firm, with straight angle and uniform arc.

3. The reinforcement of air duct shall be reliable, neat, with appropriate spacing, uniform and symmetrical.

4. When the size of the large side of the air duct is ≤ 300mm, the allowable error is 0 ~ 1mm. When the size of the large side of the air duct is > 300mm, the error is within 0 ~ 2mm.

5. The allowable error of flange inner edge dimension is 1.0 ~ 3.0mm.

6. The allowable error of air duct flatness is ± 2mm.

7. The error of diagonal difference of rectangular flange air duct is less than 3mm.

8. The allowable error of flange flatness is 0 ~ 2mm.

5. Labor arrangement plan

In combination with the construction process characteristics of the project, select a group of employees to carry out targeted technical training in advance, master the construction methods of new materials and new processes in the project, and ensure that the construction personnel can immediately put into intense construction work as soon as they enter the site, which can not only ensure the construction quality, but also improve the construction efficiency and meet the needs of all aspects of project construction.

During the peak construction period, the company will reasonably arrange 50 ventilators, 6 electric and gas welders, 5 fitters, 5 painters, 5 commissioning workers and 20 general workers to meet the construction period and quality requirements.

6. Safety precautions

1. Safety helmet and safety belt must be worn when entering the construction site.

2. During production and installation, all kinds of equipment shall be managed by special personnel.

All operating parts of the equipment shall be provided with protective measures such as protective cover, and the operating procedures of the equipment shall be strictly observed.

3. The emergency stop protection switch and leakage switch of various equipment are flexible and reliable.

4. During the on-site hoisting of the air duct, special personnel shall be assigned to command, and the selection of hoisting points shall be firm and reliable.

No one is allowed to stand under the air duct during hoisting.

5. The leakage protection switch of various small electric tools used on site shall be flexible and reliable.

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