Practical information about centrifugal ventilators

Environmental legislation plays an increasingly important role in drying and conditioning agricultural products and ventilation technology. Noise-reduction measures often lead to a choice for the noiseless centrifugal ventilator. The centrifugal ventilator, with its V-belt drive, comprises a fan casing in which the impeller vane is mounted on a shaft supported on bearings. The duo-centrifugal ventilator comprises two ventilators on one shaft supported on bearings and driven by one motor via V-belts. In the centrifugal ventilator, the direction in which the air is drawn in and the direction in which it is blown out are at right angles. The rotational speed of the motor and the pulley ratio determine the rotational speed of the impeller vane. Many factors play a role in determining the correct centrifugal ventilator for your particular situation - the people at Agratechniek are pleased to provide you with sound advice. They can talk from experience. Counterpressure in Pa Based on the conventional standards that apply to drying technology, a rough classification can be made of three main groups for the counterpressure in Pa (Pascal) for the agricultural sector: * Low pressure: 0- 75 Pa, the ventilator blows into an open space * Medium pressure: 75-250 Pa, for flower bulbs, potatoes, garlic and shallots * High pressure: 250-800 Pa, for onions (stored loosely), seeds and cereals. Available versions Various versions of centrifugal ventilators are available: Dimensions: lxbxh from 395x425x325 through 1845x1649x1540 mm (dimensions do not include those of the motor) impeller vane diameter: 200 through 1000 mm * Motor power: 1.5 kW through 37 kW * Rotational speed of motor: 720,960,1440, 2880 p/min.(or double-speed motor) * Motor position: can be located in almost any position Practical example: Centrifugal ventilator HE-630 with a 2.2 kW motor: A volume of air equal to 20,000 m_/h, at Pa 220, is the volume for which this ventilator has been designed. From this, a rotational speed results of 360 rpm. Sufficient for processing 6 boxes of product by one ventilator. If considerably more boxes are placed in front of each ventilator, the counterpressure falls significantly. Such a situation involves more motor power consumption and the current consumption (in Amperes) rises. With a slight counterpressure, the ventilator exceeds its maximum motor power. To avoid this undesirable situation, it is necessary to select a motor with ample power capacity. Regarding air delivery You achieve higher air delivery at a constant counterpressure by deploying: * An impeller vane with a larger diameter * A higher rotational speed (which demands a heavier motor). A greater counterpressure is resolved with the aid of higher rotational speeds. Maximum air delivery in the desired pressure area is achieved by controlling the rotational speed of the impeller vane by means of the correct pulley ratio. Important facts: * The centrifugal ventilator cannot be used to blow in air and draw out air alternately * The direction of the air flow is independent of the direction of rotation of the motor - if the direction of rotation is incorrect, the air delivery is significantly reduced, a detail that demands extra attention when installing the motor * V-belts and bearings must be maintained at regular intervals.