What is an explosion-proof fan: a guide to safety, application and maintenance of explosion-proof fans

Explosion-proof ventilators are widely used in explosive hazardous places in petroleum, chemical, metallurgy, pharmaceutical, electronics, aerospace, ports, warehousing and other industries to ensure the safety of explosive atmospheres. There are many types of explosion-proof ventilators, such as explosion-proof axial fans, explosion-proof centrifugal fans, explosion-proof side wall fans, explosion-proof roof fans, and so on.

The principle of explosion protection of explosion-proof ventilators is to avoid possible sparks, arcs and dangerous temperatures during their operation or operation, so as to ensure that they do not ignite the surrounding explosive atmospheres during their operation.

The drive motor of the explosion-proof ventilator is an explosion-proof motor, and the impeller and casing are made of matching materials that meet the explosion-proof requirements. The assembly of the casing and impeller of the explosion-proof ventilator, the protection of the inlet and outlet air ends, the influence of the load on the temperature rise of the motor, and the protective grounding device should also meet the requirements of explosion-proof standards.

1. General requirements for explosion-proof fans

One. Product performance requirements for explosion-proof ventilators

　　1) Under the rated speed and within the specified flow range, the deviation between the measured aerodynamic performance of the ventilator and the specified aerodynamic performance shall meet the following requirements:

　　a) Under the specified flow rate, the pressure value of the fan with the machine number less than or equal to No.10 does not exceed -8%~+ 5% of the specified value; The pressure value of the fan with machine size greater than No.10 does not exceed -5%~+5% of the specified value.

　　b) The efficiency of the ventilator shall not be less than 8% of the efficiency of its corresponding point.

　　2. The ratio of ventilator noise at the best efficiency working point to the Las value of sound level A shall comply with the provisions of JB/T 8690.

　　3. The bearing temperature rise and supporting vibration speed of the fan shall comply with the following provisions:

　　a) The bearing temperature measured on the bearing surface shall not be higher than the ambient temperature by 40 °C.

　　b) The effective value of the vibration velocity of the rigid support shall not exceed 4.6 mm/s, and the effective value of the vibration velocity of the flexible support shall not exceed 7.1 mm/s.

　　Two. Structural requirements

　　1) Basic design requirements

　　a) Under the specified working conditions, the ventilator and auxiliary equipment should be designed with a service life of at least 10 years (except for wearing parts) and a safe operation time of not less than 18 000 h before the first overhaul.

　　b) The critical speed of the rigid shaft of the fan should be more than 1.3 times the maximum working speed.

　　c) The basic type, size parameters and performance curve of the ventilator shall comply with the provisions of GB/T 3235.

　　d) In the structure of the ventilator, it is required that the rotating parts and the adjacent stationary parts avoid rubbing to prevent sparks. Other aspects such as structure, type, strength, stiffness, etc. should be satisfied: axial flow fans should comply with the relevant provisions of JB/T 10562, centrifugal fans should comply with the relevant provisions of JB/T 10563, and other ventilators should meet the provisions of relevant standards.

　　2) Impeller

　　a) The fan impeller shall be subject to the overspeed test, and the impeller shall operate at a speed of not less than 110% of the maximum working speed, with a duration of not less than 2 min, and shall comply with the provisions of JB/T 6445.

　　b) The impeller should be balanced and the quality grade should be in accordance with the provisions of JB/T 9101.

　　c) The diameter of the through hole for the rivet of the impeller rivet shall be in accordance with the relevant regulations, and the riveting quality requirements shall comply with the provisions of JB/T 10214.

　　Three. Main component material

　　a) When the fan impeller is made of aluminum alloy, the air intake chamber and casing must be made of carbon steel.

　　b) When the fan impeller is made of steel, the material of the inlet ring and rivets of the centrifugal fan must be made of brass or aluminum; The corresponding impeller part in the steel casing of the axial flow fan must be made of brass or aluminum ring and corresponding rivets.

　　c) When using other materials, materials that do not produce sparks when the rotating parts and the stationary parts collide should be selected, and the technical requirements should comply with the provisions of JB/T 10562 and JB/T 10563.

　　Four. fabricate

　　a) Casting requirements

　　The quality of iron castings should comply with the provisions of JB/T 6887.

　　The quality of steel castings should comply with the provisions of JB/T 6888.

　　The quality of aluminum alloy castings should comply with the provisions of GB/T 9438.

　　b) Riveting and welding requirements

　　The welding quality should be in accordance with the provisions of JB/T 10213.

　　The manufacture of riveting and welding parts shall comply with the provisions of JB/T 10214.

　　Other welding requirements shall be in accordance with the provisions of JB/T 10562 and JB/T 10563.

　　Five. Assembly requirements

　　a) The radial clearance between the inlet ring of the centrifugal fan and the impeller inlet should be uniform along the circumference, the radial unilateral clearance of the fan with a machine size less than or equal to No.10 is 2.5 mm~4 mm, and the radial unilateral clearance of the fan with a machine size greater than No.10 is (0.15%~0.4%) D impeller diameter, but the minimum radial unilateral clearance shall not be less than 2.5mm, and the axial overlap length is (0.8%~1.2%) D impeller diameter.

　　b) The radial clearance between the casing and the impeller of the axial flow fan should be uniform, the radial unilateral clearance of the fan with a machine size less than or equal to No.10 is 2.5mm~4mm, and the radial unilateral clearance of the fan with a machine size greater than No.10 is (0.15%~0.35%) D impeller diameter, but the minimum radial unilateral clearance shall not be less than 2.5mm.

　　Six. Safety requirements

　　a) The flameproof motor and supporting electrical accessories used in the ventilator shall comply with the provisions of GB 3836.1, GB 3836.2, GB 3836.3 and JB/T 7565.5.

　　b) The surface of the ventilator casing and the surface of the transmission assembly should have a grounding device that meets the explosion-proof requirements and a permanent grounding mark.

　　c) When the air inlet chamber of the ventilator is directly open to the atmosphere, the air inlet chamber must be equipped with a fixed protective fence (or net) to prevent foreign objects from sucking into the ventilator. In addition to considering factors such as the size of the fan number and the working environment, the structural design of the protective fence (net) should also consider the minimum airflow resistance caused by the addition of the protective fence (net).

　　d) The rotating (transmission) parts such as transmission group, coupling, pulley, belt and so on shall be guarded with safety devices and comply with the provisions of GB/T 19074. The structure of the shield should be sturdy and avoid contact with the rotating parts. In order to avoid sparks caused by static electricity accumulation on the shroud, the shroud insulated from the casing should be equipped with a reliable grounding device.

　　e) The rotating parts of the fan must be fixed firmly, and there should be measures to prevent loosening (the impeller is locked with the shaft; There are positioning measures for bearing housings, bearing housings and motors and brackets).

　　f) When the impeller spindle passes through the casing, the shaft hole of the steel casing and the passing part of the shaft should be equipped with an aluminum sealing isolation ring with a stop; The clearance between the inner bore of the sealing ring and the shaft is 0.5 mm.

　　Seven. other

　　a) The fan coating shall comply with the provisions of JB/T 6886.

　　b) The appearance and cleanliness of the ventilator shall comply with the provisions of JB/T 10562 and JB/T 10563.

2. Technical requirements for explosion-proof fans

Let's take the axial flow fan as an example to explain the explosion-proof technical requirements of the explosion-proof fan:

1. The material of the impeller and the matching material of the casing corresponding to the impeller

1) Metal fans, fan covers, and vent baffles shall comply with the provisions of the housing materials specified in Chapter 8 of GB/T 3836.1-2021:

The total content (mass percentage) of magnesium, titanium and zirconium does not exceed 7.5% for EPL Gb or Gc for Class II equipment and EPL Db or Dc for Class III equipment;

If the above material composition limits are exceeded, the equipment shall be marked with an "X" in accordance with the provisions of (GB/T 3836.1—2021 in 29.3e), and the special conditions of use shall contain sufficient information to ensure that the user can determine whether the equipment is suitable for use under specific conditions, for example, to prevent ignition hazards caused by impact or friction.

2) When the fan impeller is made of aluminum alloy, the air intake chamber and casing must be made of carbon steel;

3) When the steel material is used for the fan impeller, the corresponding impeller part in the steel casing of the axial flow fan must be made of brass or aluminum ring and the corresponding willow nails;

4) When using other materials, materials that do not produce sparks when the rotating parts and static parts collide should be selected, and the technical requirements should comply with the provisions of JB/T 10562;

5) The impeller, fan cover and vent baffle of the external fan made of non-metallic shall meet the requirements of the non-metallic shell and non-metallic parts of the shell in Chapter 7 of GB/T 3836.1-2021, but for the Class II rotary explosion-proof motor used to drive the fan, the anti-static performance of the external fan blade with a rotation linear speed of less than 50m/s may not be required.

Second, the assembly requirements of the casing and impeller

The radial clearance between the casing and the impeller of the axial flow fan should be uniform, the radial unilateral clearance of the fan with a machine size less than or equal to No.10 is 2.5mm~4mm, and the radial unilateral clearance of the fan with a machine size greater than No.10 is (0.15%~0.35%)D impeller diameter, but the minimum radial unilateral clearance shall not be less than 2.5mm.

For room ventilation fans of 5kW and below, where the fan impeller is mounted directly on the motor shaft, the gap between the fan impeller and the fan cover, vent baffle and its fasteners should be at least 1/100 of the maximum diameter of the fan impeller during normal operation. If the corresponding part is manufactured with controlled dimensional concentricity and dimensional stability (e.g. cast metal machined parts), the clearance does not have to be greater than 5 mm and can be reduced to 1 mm. In any case, this gap should not be less than 1mm.

3. Safety protection requirements for air inlet and outlet ends

The protection performance of the inlet and outlet ends of the explosion-proof ventilator shall be at least as follows:

Air inlet: IP20

Air outlet: IP10

The purpose of this is to prevent solid foreign objects with a diameter of more than 12.5 mm from coming into contact with moving parts and causing sparks.

Fourth, the influence of load on the temperature rise of the motor

Explosion-proof ventilators should avoid excessive loads and surface temperatures that exceed the ignition temperature of gases or dusts in explosive atmospheres.

5. Requirements for protective grounding devices

The protective grounding device and grounding sign that meet the requirements of the explosion-proof standard shall be set at the appropriate place on the surface of the casing of the explosion-proof ventilator and the surface of the transmission assembly; In order to avoid sparks caused by the accumulation of static electricity on the shroud, the shroud insulated from the casing should also be equipped with a reliable protective grounding device.

6. Explosion-proof qualification certificate

The structure, strength, and rigidity of the explosion-proof ventilator should be considered as a whole, and in order to ensure the explosion-proof safety performance, the explosion-proof ventilator should obtain the CCC compulsory certification certificate and the explosion-proof certificate.

3. Precautions when selecting explosion-proof fans

1. Determine the type of ventilator according to different uses. For example, when transporting clean air, you can choose a ventilator for general ventilation; When transporting corrosive gases, anti-corrosion ventilators should be selected; When transporting flammable ventilators or dusty air, explosion-proof ventilators or dust exhaust ventilators should be used.

2. Determine the model of the fan according to the required air volume, wind dust and the selected fan type.

3. In order to facilitate the connection and installation of the ventilator and the system pipeline, the appropriate ventilator outlet direction and transmission mode should be selected.

Here are some things to look out for when choosing a model.

Air volume of the fan:

The product of the wind velocity V and the cross-sectional area F of the air duct.

Since the large fan can accurately measure the wind speed with an anemometer, the air volume calculation is also very simple, and the air volume can be calculated directly with the formula Q=VF.

The determination of the number of fans needs to calculate the total air volume required by the plant according to the number of air changes in the selected room, and then calculate the number of fans.

Calculation formula:

N=V×n/Q其中：N——风机数量(台); V——场地体积(m3);

n - the number of air changes (times/hour);

Q——所选风机型号的单台风量(m3/h)。

Fan model:

The selection of fan model should be based on the actual situation of the plant, try to choose the fan model that matches the original window size, and keep a certain distance between the fan and the wet curtain as much as possible (as far as possible on both sides of the gable wall of the plant) to achieve good ventilation effect. The exhaust side should not be close to nearby buildings as much as possible to avoid affecting nearby residents.

Fan air pressure:

It refers to the resistance to be overcome during the conveying of so much air volume, and the pressure rises. However, the selection of domestic fans is generally pressed by full pressure, and foreign fans are generally pressed to rise. The residual pressure outside the machine = the full pressure of the fan - the resistance of each treatment section of the wind cabinet, the return air duct is generally 7~8Pa/m, and the resistance of the 90-degree elbow is calculated according to 10Pa/piece.

Empirical formula: external residual pressure = full pressure of the fan - resistance of each treatment section of the fan power (W) = air volume (L/S) * wind pressure (Kpa) / efficiency (75%) / force rate (75%) full pressure = static pressure + dynamic pressure. Fan motor power (W) = fan power (W) * 130% = air volume (L/S) * wind pressure (Kpa) / efficiency (75%) / force rate (75%) * 130%

Other precautions for explosion-proof fans:

When it comes to the difference in the surface treatment of explosion-proof fans and axial fans, the first thing that comes to mind is the choice of coatings. The paint used for the room temperature centrifugal induced draft fan is the same as that of the axial fan, but the high-temperature induced draft fan must be selected for the high-temperature resistant coating.

There is no difference between explosion-proof fans from the perspective of fans, and they are all driven by electric motors to rotate the fan blades to generate wind. The former is located at the back end of the boiler, blowing air to the flue outside the boiler, generating negative pressure on the furnace and guiding the flue gas, so it is called the induced draft fan; The latter is located at the front end of the boiler on the contrary and blows air into the boiler, so it is called a blower.

The condensate discharge pipe of the fan coil unit must have a certain slope to ensure that there is no water accumulation in the drip tray. For the installation of the fan coil unit, please refer to the National Building Standard Design Atlas 01K403 "Fan Coil Unit Installation". The fan coil unit in the guest room often leaks, if it is not the pipe and valve damage, it is usually caused by condensation.

With the normal operation of the explosion-proof fan, the noise cannot be eliminated. The latest research shows that as long as the wind speed exceeds 0.75 m/s, noise is generated. Of course, the lower the wind speed, the less noise is generated. Noise is harmful pollution. Is it true that when selecting a fan, the less noise the better? Low noise is good, of course, but it must be economical. The lower the noise required, the higher the cost of the fan required. For every 10 decibels decreased, the cost of the fan increases by a factor of 1 (empirical value, non-linear). Most fans have a minimum noise level and cannot be lower than 35 dBA. Therefore, when choosing a fan, it is not necessary to pursue low noise, and it can be within a reasonable range that is acceptable to you.

4. Security and application scenarios

Safety has always been a crucial consideration in industrial production and in everyday life. Explosion-proof fans play an important role in ensuring the safety of life and property. Its application scope is not only limited to industrial production sites, but also widely used in a series of flammable and explosive places, such as chemical plants, gas stations, etc. In these places, explosion-proof fans can effectively remove combustible gases, reduce the risk of explosion, and ensure the safety of personnel and equipment.

Explosion-proof fans also play an important role in everyday life. In harsh environments, such as high temperature, high humidity, etc., explosion-proof fans provide effective ventilation and cooling effects. This not only helps to maintain a good working environment, but also ensures the health and safety of workers and increases productivity.

In addition to their wide range of applications in industry and everyday life, explosion-proof fans also play a key role in the military and medical fields. In military facilities, one of the main tasks of explosion-proof fans is the elimination of flammable gases, which is essential to ensure the safety of military equipment and personnel. It can effectively maintain the gas environment in the facility, prevent the potential risk of explosion, and provide the necessary safety guarantee for military activities.

In the medical field, explosion-proof fans provide a high-quality ventilation environment and play a vital role in ensuring the health and safety of patients. In medical facilities, a good ventilation system can effectively remove harmful gases and bacteria, maintain fresh air, reduce the risk of cross-infection, and create a safe and healthy working and treatment environment for medical staff and patients.

5. Design considerations and environmental considerations

The explosion-proof fan design focuses on humanization and environmental protection. Designed to be low noise, these fans focus on reducing noise generation, employing specially designed mechanisms and materials to minimize noise during operation. This design not only improves the working environment, reduces the disturbance to the surrounding environment and personnel, but also improves the comfort of the equipment.

At the same time, the energy consumption of the fan can be effectively reduced by optimizing the structure of the fan, improving the efficiency of the motor and reducing the energy loss. This design not only helps to reduce the operating costs of enterprises, but also has a positive impact on the environment, reduces carbon emissions, and makes a substantial contribution to the cause of environmental protection.

6. The importance of maintenance and upkeep

Maintenance and upkeep are essential for the proper operation and long-term use of explosion-proof fans. The reliability and stability of explosion-proof fans are directly related to the safety and productivity of the workplace. Therefore, maintenance and upkeep work are key to ensuring the continuous and efficient operation of explosion-proof fans.

First of all, regular maintenance can detect and repair potential problems in a timely manner, reducing the risk of equipment failure. Regularly inspect all parts of the explosion-proof fan, including but not limited to the motor, fan blade, air duct, etc., which will help to detect abnormal operation, wear or loosening and other problems in time. Through regular maintenance, these problems can be dealt with in a timely manner, preventing small faults from gradually turning into serious problems and ensuring the stable operation of the wind turbine.

Secondly, regular cleaning and maintenance are also key to ensuring stable fan performance. Removing dust, debris, etc. from the inside of the fan and keeping parts clean and integrity helps to reduce friction and overheating caused by dirt and extend the service life of parts.

In addition, regular replacement of worn parts is also an important part of maintenance. When it is found that the internal components of the fan are worn or aged, they need to be replaced in time to keep the fan in good condition. Select the original parts that meet the specifications for replacement to ensure the normal operation of the fan.

Maintaining records is also important. Recording the time, content, replaced parts and other information of maintenance is helpful to track the maintenance history of explosion-proof fans, formulate more scientific and reasonable maintenance plans, and provide reference and guidance for follow-up maintenance.

Here are the key points from the maintenance process:

1. Regular inspection and cleaning: Check and clean the operating status and components of the fan, and pay attention not to damage its components.

2. Replacement of parts: Wear or damaged parts should be replaced in time, and parts that match the original equipment should be selected.

3. Adjustment of operating parameters: Adjust the operating parameters of the fan to suit the working environment as needed.

4. Record maintenance information: Record maintenance time, content, replacement parts and other information during maintenance as a reference.

7. Other precautions in the maintenance process

1. Anti-corrosion measures: Explosion-proof fans may be exposed to corrosive gases or liquids during operation, which may cause damage to the components of the fan. Therefore, when selecting and using explosion-proof fans, their corrosion resistance must be considered. Measures such as applying anti-corrosion coatings or using corrosion-resistant materials can be taken to enhance the durability of the fan against corrosive environments. Regular inspections and preventive maintenance, timely cleaning and application of anti-corrosion coatings can effectively protect wind turbine components from corrosion.

2. Maintain tightness: Explosion-proof fans need to maintain good sealing performance during operation to prevent the leakage of hazardous substances such as combustible gases. Regularly inspect the seals of the fan, such as seals or seams, to ensure their integrity and tightness. When a deterioration or damage to the seal is found, it needs to be repaired or replaced in time to prevent the leakage of hazardous materials and ensure the safety of the working environment.

3. Installation specifications: The installation process of the wind turbine needs to follow the relevant specifications to ensure its normal operation and service life. During the installation process, special attention needs to be paid to the details of the position selection, angle adjustment and fixing method of the fan. Ensure that the fan is installed securely and properly in the designated location, and meets the standards for safe and stable operation.

4. Operational monitoring: Continuous operation monitoring is essential for explosion-proof fans, which helps to grasp the operating status of the wind turbine in real time and detect potential problems in advance. The monitoring content includes the recording of air volume, wind pressure, temperature, vibration and other parameters, and pays attention to the working status and abnormal sound of the fan. Through regular monitoring, abnormal conditions in the operation of the wind turbine can be identified in time, so that preventive measures or timely maintenance can be taken to ensure the continuous and stable operation of the wind turbine.

5. Maintenance Personnel Requirements: Personnel who maintain explosion-proof fans need to have the corresponding professional knowledge and skills to ensure the proper operation and maintenance of the fans. Trainers need to understand the relevant safety operating procedures and maintenance procedures, and strictly follow the operation guidelines to ensure the safety and health of workers during the maintenance process.