Under design conditions, a fan with a wind pressure of 30 kPa to 200 kPa or a compression ratio e of 1.3 to 3 is called a blower. Blowers are often used as vacuum pumps and for pneumatic conveying and are widely used in various environments in production and daily life.
I. Working Principle of Centrifugal Blowers
When the motor rotates and drives the fan impeller to rotate, the gas between the blades in the impeller also rotates. Under the action of centrifugal force, this gas is thrown out. The gas flow velocity increases, converting kinetic energy into static pressure energy during the flow. Then, with the pressurization of the fluid, the static pressure energy is converted into velocity energy again, and the gas is discharged through the exhaust port. A certain negative pressure is formed in the middle of the impeller. Due to the negative pressure at the inlet, the external gas is immediately replenished under the action of atmospheric pressure. Under the continuous rotation of the impeller, gas is continuously discharged and replenished, thus achieving the purpose of continuous blowing.
II. Classification of Blowers
According to the pressure of the blower, fans can be divided into low-pressure fans, medium-pressure fans, and high-pressure fans. The pressure ranges are as follows: for low-pressure fans, the total pressure H is less than or equal to 1000 Pa; for medium-pressure fans, 1000 Pa < H is less than or equal to 3000 Pa; for high-pressure (centrifugal fans), 3000 Pa < H is less than or equal to 15000 Pa.
III. Characteristics of Blowers
- Since the impeller operates without friction inside the machine body and does not require lubrication, the discharged gas does not contain oil. It is an ideal pneumatic conveying air source for industries such as chemical and food.
- Blowers are positive displacement blowers. The selection range of pressure is very wide, and the selection of flow rate can be achieved by selecting the rotational speed.
- The rotational speed of the blower is relatively high, and the gap between the rotor and the rotor and between the rotor and the body is small, resulting in less leakage and higher volumetric efficiency.
- The rotors of the blower have all undergone static and dynamic balance checks. The finished product operates smoothly with minimal vibration.
IV. Installation Precautions for Blowers
- The surrounding area of the blower should be as wide as possible to facilitate disassembly, assembly, and daily inspection. When installed outdoors, a rain shelter should be set up; when installed indoors, good ventilation should be maintained.
- The concrete foundation of the unit should comply with the regulations of relevant materials for equipment installation and machine foundation. When designing the foundation, users should fully consider the weight of the blower and the pressure resistance of the foundation. The surface of the foundation should be kept as horizontal as possible and sufficient reserved holes for anchor bolts should be left.
- Place the blower on the foundation and insert shims at appropriate positions between the unit base and the foundation surface to make the unit evenly supported. After leveling the unit, conduct secondary grouting. After the cement mortar solidifies, evenly tighten the anchor bolt nuts at the same time.
- Before installing the pipeline, thoroughly remove foreign matters such as rust and welding slag in the piping to avoid serious accidents caused by mixing into the cylinder.
- To ensure the long-term safe operation of the blower, an air filter or vacuum filter must be installed on the intake pipeline. To effectively reduce the noise of the blower, the mufflers at the inlet and outlet should be installed as close as possible to the inlet and outlet of the blower according to the calibrated airflow direction.
- The elastic joint should be close to the inlet and outlet ends of the blower. It not only compensates for the installation error of the piping but also can reduce the transmission of vibration along the rigid pipeline when the blower is running.
- On the exhaust pipeline close to the blower, depending on the load situation, consider arranging a vent bypass and configuring a muffler to facilitate the no-load start and unload stop of the blower.
- The exhaust side of the blower is better equipped with a safety valve and a check valve. The intake side of the vacuum pump is equipped with a vacuum safety valve. Pressure gauges should be installed on the inlet and exhaust sides of the blower, and a vacuum gauge should be installed on the intake side of the vacuum pump.
- There should not be too many bends in the pipeline. At the same time, try to avoid using 90° right-angle bends. All pipelines should be provided with reliable supports to prevent the fan from bearing unfavorable additional loads.
- Voltage meters and ammeters should be installed on the power supply.
V. Usage Precautions for Blowers
- The boost pressure of the blower must not exceed the pressure value specified on the nameplate. Overload operation will damage the fan and motor and may even cause more serious quality accidents.
- During operation, the bearing temperature rise should not exceed 75°C, and the lubricating oil temperature rise should not be higher than 45°C. When the oil temperature is high in summer, it is recommended to use Shell Omala 220# lubricating oil.
- During operation, attention must be paid to the operation of the fan. In case of abnormalities, the machine should be stopped immediately for inspection, and pay attention to the readings of the power meter. At the same time, regularly check the bearing temperature, lubricating oil temperature, lubricating oil level, etc., and make records.
- If the safety valve opens frequently or continuously during operation, the machine should be stopped immediately to check whether the system is overpressurized. Only after the problem is solved can the test run be carried out again.
- When the system flow needs to be adjusted, it is not allowed to adjust by reducing the valve opening. The flow adjustment of Roots blowers can be achieved by diverting or changing the rotational speed within the allowable range.
- When using water-cooled products, keep the waterway unobstructed. If it is停用, drain the cooling water from all parts and dry it.
- When the oil level gauge is seriously contaminated, it should be cleaned or replaced in time so that the oil level can be clearly observed to ensure normal lubrication of the fan.
VI. Maintenance Points for Blowers
- Hard objects, dust bag powder particles, fibers, and water droplets should be removed before entering the fan. This can be handled by using a dust collection bag. If a filter is installed in the pipeline, to avoid pressure drop loss, please use a large-area filter and regularly clean the pollutants in the filter.
- The inside and outside of the fan should be cleaned regularly to remove surface dust. If a large amount of dust accumulates, the heat dissipation effect will become worse, which may cause a temperature rise, a reduction in air volume, an increase in vibration, and eventually lead to a failure.
- Bearings, oil seals, and mufflers are consumables and therefore have a certain lifespan and need to be replaced regularly. At the same time, blades, casings, metal meshes, etc. also need to be replaced regularly according to the usage environment
