Ventilation volute: features of an exhaust centrifugal fan. Hood for domestic and industrial use

Description of equipment

Centrifugal fans are characterized by excellent efficiency, which is achieved due to the rapid rotation of a radial wheel with numerous blades. The working element is located in a spiral chamber, which ensures the highest possible air injection efficiency. The blades on the wheel are made curved, straight or in the shape of a bird's wing. Accordingly, the size of the equipment, its performance and purpose vary.

Depending on the air flow pressure indicators, it is customary to distinguish three classes of centrifugal fans:

low pressure;
medium power;
heavy duty installations.

The pressure indicator can vary in the range of 0.1-12 kPa. The performance of the equipment will depend on the profile and number of blades, as well as on the electric motor used, which is responsible for rotating the working element. On sale you can find both fully mechanical devices and installations that are controlled automatically and have expanded functionality.

All snail coolers used today can work both to blow in and remove air from the room. To change the direction of rotation of the impeller, the phases of the current at the motor terminals are swapped. This is done using the corresponding switch toggle switch on the device control unit. Some models of ventilation equipment have the ability to change the rotation speed, which allows you to adjust the performance of the blowers.

Operating principle and design

Centrifugal fans, designed to move air and a mixture of gases, are made of durable materials that allow the unit to withstand elevated temperatures. The design consists of a rotating wheel with blades attached to it. The working part is connected to the shaft of an electric motor responsible for rotating and pumping air. The operating principle of the hood is as follows:

1. Air is sucked into the housing by the rotor through the inlet.
2. Air masses receive rotational movement.
3. Due to the centrifugal force created by the rotating blades, high-pressure air is forced to the outlet located in the spiral casing.

The special design of the fan makes it possible to provide high pressure and excellent performance even with low power electric motors. Due to their compact size, blowers can be used in household ventilation and smoke removal systems.

Design features

A snail hood is a radial fan built into a specially shaped housing, reminiscent of a snail's shell. Air is directed into it under the influence of centrifugal force.

The centrifugal fan consists of the following parts:

Spiral shaped body.
The suction pipe is round in shape, the diameter size coincides with the size of the impeller.
An exhaust duct ending in an outlet pipe.
The outlet pipe is rectangular in shape and is located with the throat facing up.
Impeller with blades.
Electric motor.

The center of the housing is occupied by the fan impeller. Its blades differ from the usual large ones, starting from the axis of rotation. In a radial fan, the impeller blades are rectangular, straight or curved in a certain way, and are located along the rim of the circle of rotation.

The shape of the snail hood blades depending on the purpose:

straight – for removing volatile suspended matter (dust, small chips);
with the blade bent backwards - to increase the speed of rotation of the wheel with reduced noise generation;
with the blade bent forward - to increase the pressure and efficiency of the engine.

The design features of a radial fan lie in the different ways of transmitting torque from the engine to the impeller:

The impeller is “mounted” directly on the motor shaft. This design is simple and accessible. However, if the fan breaks down, it must be completely disassembled for repair work.
Torque is transmitted via a belt. A common type of interaction between a motor and rotating parts of a mechanism, which opens up many possibilities for manipulating pulley sizes and speeds. The belt drive makes the device more bulky and expensive.
The impeller is connected to the motor shaft through a coupling. This fit relieves the load on the engine bearings without increasing the complexity and metal consumption of the design. This type of snail hood can be considered the best in terms of maintainability and price.

We recommend that you read: Ventilation in the sewer system in a private house

The speed of a snail-type hood is regulated not only by the power of the motor, but also by the number of blades on the impeller. The fan housing is made of steel, alloys or aluminum. To protect against corrosion, steel parts are painted or coated with special protection.

Types of centrifugal radial fans

There is no fundamental difference in design between radial fans. They are divided into several types according to purpose and power.

By power

The working pressure that the volute hood is capable of depends on the engine power of the device, the number and configuration of the impeller blades.

There are 3 types of radial fans according to this parameter:

Relatively low pressure devices (up to 100 kg/cm²). These are small fans used to create forced ventilation in residential buildings, labeled as BP 80-75. In apartment buildings, such devices are mounted on the roof, in a common ventilation duct.
Devices that operate in the medium pressure range from 100 to 300 kg/cm². They are used in ventilation systems of production workshops without special safety requirements. The general marking of hoods of this group is BP 300-45.
Powerful (working pressure in the range from 300 to 1200 kg/cm²) snail hoods are installed in hazardous industries where there is a need for intensive removal of caustic, flammable and explosive gas mixtures. The general marking of this class is VR 12-26.

Which fan should be chosen for a given ventilation system is influenced by many parameters: the length of the channels, their branching, throughput, and the required air exchange rate per unit time. Such calculations are carried out by specialists at the design stage of the ventilation system.

Note! Centrifugal fans are installed not only for exhaust, but also for air supply, for example, in boiler rooms.

By purpose

The second classification system for radial fans divides them according to their purpose:

General purpose snail hoods. They are operated at temperatures up to +80 degrees in an atmosphere where there are no specific or dangerous contaminants. Installed in residential or industrial sectors.
Explosion-proof - the body and parts of the mechanism are made of materials that prevent the occurrence of sparks during operation. Used in rooms where there are explosive gas mixtures. The permissible operating temperature range is from -30 to +40 degrees.
Fire-resistant or heat-resistant hoods are installed in industries that use increased temperature in the technological process. The devices are made of carbon steel and coated with heat-resistant compounds. Operate at temperatures up to +200 Celsius.
With enhanced anti-corrosion protection. These are fans that are installed in chemical plants with aggressive environments.
Dust (marked VRP) – fans for removing air masses with suspended particles. The devices have a larger gap between the housing and the impeller and a reduced number of blades so that the device does not become clogged with waste during operation. Design features here lead to a drop in the efficiency of the device. It is necessary to choose a hood with a reserve of operating power.
For smoke removal (marking VRDU). These fans are installed to remove smoke if a fire occurs. The devices operate in the temperature range of 400-600 degrees.

Do it yourself

Building a scroll fan is not the most difficult thing if you decide to take on a homemade unit with your own hands.

There are several important recommendations that you should consider before building your own snail fan.

Functional purpose. To equip a part of a room, a small area or equipment with a ventilation system, the housing can be assembled from scrap materials. If this is a centrifugal unit that will generate air flows to ensure the operation of boiler equipment, then the housing is made by hand using stainless steel or heat-resistant metal.
Power. This parameter directly depends on the functions that the centrifugal unit will perform. Many home craftsmen use snails removed from old equipment, ventilation systems, hoods or vacuum cleaners. By using such a unit, you guarantee an exact balance between power and body characteristics.

If you want to make a snail for domestic use or for use inside a workshop, then you can assemble the device yourself. All other situations imply the need to use only factory-proven, proven snails.

To assemble an effective homemade snail fan with your own hands, you will need to complete the following tasks:

Calculate the dimensions of future equipment. If this is a centrifugal unit for installation in a confined space, be sure to use damper pads. They will compensate for the vibrations generated during its operation and protect the volute from premature wear. If this is a large stationary unit, vibration protection occurs due to the weight of the equipment and its fixation;
Make a fan casing. If you do not have a ready-made box that is ideal for the fan, use scrap materials. Plastic, plywood sheets, and steel are suitable for these purposes. If you decide to take sheets of plywood, make sure that during the process of assembling the structure there are absolutely no gaps and all seams are properly sealed;
Think over the diagram of the snail's power unit. The job of the power plant is to rotate the fan blades. When choosing, consider how much power the snail has. If it is a high power centrifugal fan, use a belt drive. In small installations, it is important to use a shaft that connects the motor gearbox to the rotor;
Use fasteners. When installing a scroll fan on the outer casing of the structure, U-shaped mounting plates are used. If the power of the units is impressive, then be sure to adopt a massive, durable base;
Minimize noise. A high-power volute is characterized by the fact that such a centrifugal fan emits quite a lot of noise. Objectively, the best way to protect yourself from snail noise is to assemble the equipment with the highest quality possible. After assembling the cochlea, it is problematic to compensate for the noise. The noisiest models are those whose body is made of plastic and metal. Wooden cases reduce snail noise, but are significantly inferior to their metal and plastic counterparts in terms of service life.

According to the presented diagram, you can create centrifugal exhaust devices of various power purposes with your own hands. If necessary, you can make changes to the circuit, change components, add auxiliary elements.

The most significant point when assembling a fan with your own hands is the reliable sealing of all seams in the structure and the protection of the engine itself. Over time and with use, an engine that does not have proper protection can become exposed to various debris, dust, dirt and moisture. It is no secret that this leads to wear, gradual destruction and failure of equipment.

The mechanism of any fan is based on a rotor with blades attached to it. Their purpose is to move large masses of air for the purpose of air circulation.

The scope of application of centrifugal fans "snail" is very wide. They are used in engineering systems of buildings, industrial ventilation systems, drying chambers, household appliances, painting, and blowing machines.

How to buy a “Snail” fan

Selecting a centrifugal fan

When choosing a radial fan, you should pay attention to:

characteristics - performance, pressure, electric motor power, supply voltage;
installation and overall dimensions, diameter of nozzles, design of connections with air ducts;
purpose - for work in normal or aggressive environments;
Availability of automation, performance control and protection equipment.

The price of “Snail” fans depends on the manufacturer, size and purpose. For work in a normal environment, a general-purpose unit that is inexpensive is suitable. If the atmosphere contains corrosive gases, you will have to buy a special purpose fan at a higher price.

Do it yourself

Building a scroll fan is not the most difficult thing if you decide to take on a homemade unit with your own hands.

Functional purpose. To equip a part of a room, a small area or equipment with a ventilation system, the housing can be assembled from scrap materials. If this is a centrifugal unit that will generate air flows to ensure the operation of boiler equipment, then the housing is made by hand using stainless steel or heat-resistant metal.
Power. This parameter directly depends on the functions that the centrifugal unit will perform. Many home craftsmen use snails removed from old equipment, ventilation systems, hoods or vacuum cleaners. By using such a unit, you guarantee an exact balance between power and body characteristics.

If you want to make a snail for domestic use or for use inside a workshop, then you can assemble the device yourself. All other situations imply the need to use only factory-proven, proven snails.

To assemble an effective homemade snail fan with your own hands, you will need to complete the following tasks:

Calculate the dimensions of future equipment. If this is a centrifugal unit for installation in a confined space, be sure to use damper pads. They will compensate for the vibrations generated during its operation and protect the volute from premature wear. If this is a large stationary unit, vibration protection occurs due to the weight of the equipment and its fixation;
Make a fan casing. If you do not have a ready-made box that is ideal for the fan, use scrap materials. Plastic, plywood sheets, and steel are suitable for these purposes. If you decide to take sheets of plywood, make sure that during the process of assembling the structure there are absolutely no gaps and all seams are properly sealed;
Think over the diagram of the snail's power unit. The job of the power plant is to rotate the fan blades. When choosing, consider how much power the snail has. If it is a high power centrifugal fan, use a belt drive. In small installations, it is important to use a shaft that connects the motor gearbox to the rotor;
Use fasteners. When installing a scroll fan on the outer casing of the structure, U-shaped mounting plates are used. If the power of the units is impressive, then be sure to adopt a massive, durable base;
Minimize noise. A high-power volute is characterized by the fact that such a centrifugal fan emits quite a lot of noise. Objectively, the best way to protect yourself from snail noise is to assemble the equipment with the highest quality possible. After assembling the cochlea, it is problematic to compensate for the noise. The noisiest models are those whose body is made of plastic and metal. Wooden cases reduce snail noise, but are significantly inferior to their metal and plastic counterparts in terms of service life.

A low-power centrifugal fan will be of little use. Even quiet hoods are equipped with commutator motors that make a lot of noise. If the fact doesn’t frighten you, let’s proceed to choosing funds. We'll show you how to make a centrifugal fan with your own hands from scrap items. If in a typical axial fan the motor and impeller are important, here, in addition to everything else, the housing is added. Let's try to assemble a centrifugal fan ourselves.

Advantages and disadvantages

The ventilation volute combines reliable design and excellent efficiency. The advantages of this type of equipment include:

affordable price;
ease of operation, maintenance and repair;
reliability and wear resistance;
performance.

Disadvantages include difficulties in adjusting power and rotation speed. Such operating features are typical for fans equipped with an asynchronous motor. If it is necessary to change the rotation speed, it is necessary to purchase units with advanced automatic control, which leads to an increase in the cost of the equipment.

Housing material

The purpose and power indicators of the device will largely depend on the material from which the cooler is made. The industrial volute for ventilation is made of steel and other heavy-duty alloys, taking into account the degree of aggressiveness of the environment of use. Fan models designed for operation with non-aggressive gas mixtures and oxygen can be made of carbon and galvanized steel.

When the device is used to move aggressive gas mixtures and acids, it is necessary to choose chemically resistant steels, which ensures reliable and trouble-free operation of the equipment.

Standard modifications of exhaust fans are designed for use with air masses and gases whose temperature does not exceed 90 °C. On sale you can find highly specialized models used to work with gases with temperatures up to 200 °C. Such units are made of special heat-resistant steel, which is resistant to acids.

There is also an explosion-proof version of the hood, made of aluminum, copper alloys and other ductile metals. These snails use a special electrical wire that eliminates sparking, which is the main cause of explosions and fires.

If it is necessary to use centrifugal fans in conditions of high humidity, modifications protected from corrosion processes are used. The volute body is made of special galvanized steel, and the presence of rubberized gaskets prevents the penetration of moisture into the protected housing where the electric motor and control automation are located.

If the technological process involves active dust formation and the presence of sawdust and other mechanical mixtures in the air, then it is not possible to use standard modifications of radial fans. It is necessary to choose special dust-proof installations that do not have an additional front disk on the impeller, and the number of blades on the shaft reaches 6-8 pieces.

Another feature of this type of equipment is the presence of a large gap between the suction port and the impeller. This design allows you to cope with dust without reducing the efficiency of the equipment.

Disassembling the device: step-by-step instructions

Dismantling external ventilation parts

To remove the engine, it is necessary to disassemble the external parts of the kitchen ventilation. In this case, you can gain access to the engine system.

To do this you need to take the necessary tools and materials.

When the motor is removed from the device, the resistance of its windings is checked. To do this, prepare in advance a bundle of wires that go from the board to the electric motor. In this case, you can simultaneously diagnose faults in the motor and try to repair it without removing it from the hood. The method is less convenient, since a complex of additional work will first be required. It is better to dismantle the engine itself and not touch other parts in the ventilation housing.

Cleaning and checking

After cleaning all the grooves, dry the small parts well. Cleaning can be done with a soft cloth that does not leave streaks or scratch the surface. After cleaning, the serviceability of the engine is checked. The problem of its failure to work could be due to clogging of parts. After cleaning, the structure can become serviceable.

When the motor is installed in place, its performance is checked. If the problem also persists, the ventilation works very poorly, which means the engine needs to be replaced or some of its components are broken. The device is again removed from the fan and its performance is checked in detail.

Testing and assembly

The engine may gain speed when turned on when cranking it manually. This situation indicates a fault in the starting winding. It needs to be removed from the electric motor and replaced.

The converter adapter is also checked with a tester to ensure it matches the voltage required for operation. When using a standard 220 V LED lamp in the system, repairs only involve cleaning the contacts in the lamp base.

Types of impeller

The fan performance will directly depend on the shape, size and material of the impeller. It is also necessary to take into account the number and shape of the blades responsible for pumping pressure inside the cochlea. The main requirements for the material of the impeller and blades are corrosion resistance and ductility. Such a working body will withstand the chemical influences of an aggressive environment and increased vibration loads.

When choosing the shape and number of blades, aerodynamic loads and rotation speed are taken into account. When using powerful engines, the metal blades must be bent at right angles, which allows the formation of a stable air flow. But for low-power fans, it is preferable to use large straight blades, which make it possible to provide high pressure in large-sized volutes.

A well-made wheel should not vibrate during operation, as this can lead to rapid failure of the unit. Fan vibration increases the noise level, destroys the installation base and negatively affects the overall durability of the equipment. Oscillatory movements can be minimized by carefully balancing the shaft or using special shock-absorbing springs. They are mounted under the base of the housing, allowing them to dampen longitudinal and transverse parasitic vibrations of the unit.

Electric motors used

The industrial snail hood is equipped with explosion-proof electric motors, durable housings and covers. Most often, asynchronous mechanisms with a fixed rotation speed are used as a drive. This unit quickly reaches maximum performance and is reliable and durable. The disadvantages of asynchronous electric motors include the inability to adjust the speed of rotation of the working shaft, which somewhat limits the possibilities of using such equipment.

The presence of dimming in the electric motor and an automatic control unit allows you to regulate the rotation speed, significantly expanding the functionality of the use of volute fans. The disadvantage of using such motors with variable speed control is their high cost, as well as reduced reliability of units in which the electronics that control the operation of the drive often fail.

Self-production

Let's consider how you can create a snail fan with your own hands, the drawings of which can be found on the Internet or made yourself.

Drawing

Video review

Working wheel

First of all, you need to get an impeller. This is important because it is a fairly massive element and requires good balancing . If the impeller beats even a little, the bearings of the electric motor (or its own drive shaft) will quickly fail. Ready-made impellers from fans or air conditioners are often used, but if you can’t find them, you’ll have to make them yourself.

Landing sleeve

First of all, you need to make a landing coupling. It is made on a lathe . The coupling is then attached to the sheet metal by welding or screws, clamped in a lathe and carefully centered. The result is a round disk with a seating sleeve in the center. Markings are made on it and the blades are attached. Making a drum-type impeller with your own hands is impractical, since high-quality balancing of homemade elements is impossible.

How does a snail hood work?

The device operates from the mains. Sizes range from household (main body diameter 25 cm) to industrial (diameter 150 cm).

The fan “rakes” air with small blades that rotate at high speed. The air flow is directed into the housing, makes a turn and is removed into the outlet hole. Passing through the curls, the flow loses speed and creates pressure.

Note! If the fan inlet is hermetically connected to a closed channel, then the volute hood will work like a vacuum pump.

Supercharger sizes

The dimensions of snail fans vary significantly. You can choose a snail for an air conditioning system in a private home, or purchase powerful, productive industrial units. Hood sizes vary from 250 to 1500 mm. Depending on the dimensions and intended use, the fan can be manufactured as a single product or have a modular design with main components that can be easily replaced. The latter option allows you to modernize the equipment used at minimal cost.