Fans are vane machines designed to move air or other gases at a pressure not exceeding 15000 Pa.

Fans are conventionally divided by the developed pressure into fans:

• low pressure – up to 1000 Pa;
• medium pressure — from 1000Pa to 3000 Pa;
• high pressure – over 3000 Pa.

According to the principle of operation and device, they are divided into:

• radial (centrifugal);
• axial;
• diametrical

Radial fans. In radial fans, the flow of air or gas entering the rotating impeller changes the direction of movement from axial to radial. Radial fans, in comparison with axial fans, develop more pressure, since energy is imparted to a unit volume of transported air when moving from the radius of the entrance to the radius of the exit of the wheel.

Axial fans. In axial fans, the air flow, as opposed to radial, does not change its direction – it enters and exits along the axis of rotation of the wheel. In the simplest case, an axial fan consists of an impeller mounted on an electric motor and a cylindrical casing (shell). The design can be supplemented with inlet guide vanes and / or straightening devices.

The guide vane creates a twist of the flow at the wheel inlet against the direction of rotation. The straightening device is designed to combat the swirling of the flow behind the wheel, which is a source of pressure losses, both in the fan itself and in the elements that interface the fan with the network.

Smoke exhaust fans are special equipment used in supply and exhaust ventilation systems.

These units are used in industrial and industrial premises, in shopping centers and in other places where there is a risk of fire. Smoke extraction exhaust fans are produced in various designs.

The following types of smoke exhaust fans are distinguished:

• The roof smoke exhaust fans are adapted for installation on the roof, squat and resistant to atmospheric precipitation.
• Radial or centrifugal smoke exhaust fans. Installed in the duct system. They include impellers with forward or backward curved blades and an electric motor.
• Axial smoke exhaust fans, which are part of stationary emergency ventilation systems, are distinguished by their high efficiency and the ability to move large air flows.

Mine fans are stationary mine equipment used to provide air exchange in underground mine workings. Mine fans also include fans for ventilating tunnels and metro stations.

By the principle of action, they are divided into two groups:

• centrifugal mine fans
  axial shaft fans

By the nature of use, they are divided into three groups:

• mine fans for main ventilation
  mine fans of local ventilation
  fans of the main ventilation of tunnels and metro stations

An air heater (air heater) is one of the main elements of the ventilation system, which provides heating of the incoming supply air to the required temperature. Heaters are of the following types:

• water or steam – the air is heated by passing through the heated circuit of plates or tubes in which hot water or steam flows;
• electric – the air is heated by passing heated electrical elements through the circuit;
• gas – the air is heated when passing near burning gas burners.

Air coolers are heat exchange units that are successfully used to cool air in refrigerators, in industry and at home. Despite the variety of air conditioning equipment cooling air masses, there are only three types of air coolers:

• Superficial or dry. In such devices, heated air masses are cooled due to contact with a heat exchanger, in the pipes of which freon boils or cold water passes. This is the most common type of installation, which has only one drawback: to defrost ice on the heat exchanger, you should periodically use heat sources, such as heating elements.
• Contact or wet. In such installations, there is a direct heat exchange between air and cold water, which was previously cooled in the evaporator. With the help of a fan, the air flow is driven through a nozzle cooled in water. Such devices are also designed to use water (brine) nozzles. Such a water air cooler has a serious drawback, increased corrosion of the metal parts of the device, due to the enrichment of water with oxygen.
• Mixed (combined) air coolers. In combined installations, the water is cooled by sprinkling the freon evaporator, after which it cools the air mixture passing through the water. The air flow is generated by fans.

Draft machines are devices that provide forced movement of air and flue gases in technological systems of boiler plants, industrial furnaces and other systems for burning fuel in furnaces.

As a rule, they are rotary vane injection machines with 1-2 stages, increasing the pressure of the medium by 0.6-3 kPa.

According to the method of operation, draft machines are divided into smoke exhausters and fans.

The smoke exhausters work on combustion products removed from the installation. Externally, the smoke exhauster can be distinguished from the fan by the presence of thermal insulation on it.

The mechanism of action of the smoke exhauster: With the help of the movement of the wheel, air moves to the middle of the structure, is thrown out by the wall of the smoke exhauster, and enters the boiler furnace, where fresh air is supplied. Combustion products are removed. Smoke exhausters are installed after heating surfaces. They work in an aggressive environment: they corrode under the influence of flue gases, therefore they have low wear resistance.

The fans are designed to draw air from outside and supply it to the furnaces of steam boilers. They are installed in front of heating surfaces. Wear rate is lower than that of smoke exhausters

Types of smoke exhausters depending on the boiler equipment:

• Solid fuel.
• Pyrolysis (solid fuel is pre-processed).
• Gas (used both main and liquefied gas).

The principle of action is distinguished:

• Centrifugal smoke exhausters: designed for gas boilers, have thick walls and a 32-blade impeller. After entering the axis, the gas is scattered around the periphery.
• Injection type smoke exhausters: designed for solid fuel and gas, have 16 blades; work on the principle of one-way suction.

Blowing fans: used in steam boilers; 32 blades, work on the principle of suction.