Frequency, definition and change of rotation of the fan

Fans are an integral part of ventilation, air conditioning and heating systems. They are used both in industrial premises and in residential buildings to ensure better air circulation or exhaust.

An example of a fan used in industrial premises

This device is a device consisting of a propeller and an electric motor that drives them. According to the type of installation, they are divided into indoor and roof mounted. How to determine which direction the blades are spinning? How to change the side of rotation? How to determine the frequency of revolutions? This is what will be discussed further.

Definition of the side of rotation

Determining the direction of movement of the impeller is very simple. Often the direction of rotation is marked in the form of an arrow. The arrow indicates the side in which the impeller rotates. If for some reason there is no indication of the direction of movement, then determining the right side will not be difficult without it.

An example of a direction indicator of movement of a "snail"

To determine the direction of the blades, it is necessary to look at the structure from the side of the hole through which air is drawn in. If the impeller rotates clockwise and the “snail” type case is twisted clockwise, the movement is right. If the revolutions of the blades go counterclockwise, the side is left.

How to determine the fan speed?

The speed indicates its installation performance. In order to calculate the frequency of movement of the impeller, a device called a tachometer is used. For a more accurate determination, it is recommended to use tachometers of accuracy class 0.5 or 1.

Tachometers differ at the installation site and are divided into:

• stationary;
• remote;
• tame.

Also, tachometers differ in principle of action. They are mechanical, magnetic, magnetic induction and electronic.

Modern electronic tachometer in action

Consider the example shown in the picture. Using a laser beam aimed at the wheel, the measurement of speed (rpm). All data is displayed on a small display.

How to change the direction of rotation of the propeller?

Sometimes such situations occur when you need to change the side of rotation of the blades. For such purposes reversible fans are used. Their main difference is that the reversing fan is designed for possible changes in direction, but the usual one is not.

Reversible model

Reverse models were widely used at mine enterprises. They serve both for air supply and for its exhaust.

Reversible axial models used in mines

Changing the direction of movement of axial models is carried out in two main ways:

• Without changing the direction of rotation.
• With a change of direction.

When applying the second method without changing the position of the blades, the system does not work at full strength. The wheel runs backward, which reduces the efficiency. In order to get 100% of productivity during reverse, it is necessary to change the position of the blades.

In order to change the direction of rotation of the propeller, it is necessary to disassemble the engine and change the phases:

• On a single-phase output motor, we have 4 wires. 2 wires to the beginning of the winding and 2 from the end. To reverse, it is necessary to transfer the phase and zero from the beginning of the winding to the end.
• In the case of a three-phase motor, we have 6 wires at the output. 3 at the beginning of the winding and 3 at its end.To reverse in a three-phase network, we need to swap any two wires at the input.
• To reverse a three-phase electric motor with connection to a single-phase network through a starting capacitor, it is necessary to interchange the cable going to the input of the capacitor with a cable that is not connected to it.

In order to change the direction of the propeller of the exhaust hood (kitchen hood), there are two working methods:

1. If an induction motor is installed in the hood structure, the change is made by throwing wires (the method is described above).
2. In the case of a phase-shifting capacitor, the change is made by means of its permutation. For the correct execution of this method, it is recommended to turn to the services of an experienced electrician.

Exhaust hood

Summarize. The direction of travel of the wheel is determined either by the arrow drawn on the housing or the impeller, or by the side view.

To measure the rotational speed of the blades, a device called a tachometer is used. They are both old mechanical and modern, reading information using a laser beam.

To change the direction of rotation of the blades, we just need to change the necessary contacts on the electric motor. If after changing the direction side it is not possible to change the position of the blades, then the efficiency and its performance will drop by about 30% of the norm (depending on the type).

All these procedures can be performed without much effort and with your own hands.