The terms behind the numbers on your datasheet.
Plain-English definitions of the centrifugal-fan terms that show up on a datasheet, a GA drawing or an enquiry — engineer to engineer.
The actual shaft power a fan draws at its operating point, before drive and motor losses; it must be established at the real duty and density so the motor is sized with adequate margin. read more →
Backward-curved blades with a wing-shaped hollow or solid profile that minimises turbulence, delivering the highest efficiency and lowest noise of any centrifugal wheel on clean-air duty. read more →
The adjustment of a fan's rated performance (quoted at standard air) for the actual gas density set by temperature, altitude, moisture and composition; pressure and power scale directly with density while volume flow does not. read more →
A classification of how often an explosive atmosphere is present — gas Zones 0/1/2 and dust Zones 20/21/22; a fan for a hazardous area is built and self-declared suitable for the specified zone rather than certified by a notified body. read more →
Blades that lean away from the direction of rotation, giving high efficiency and a non-overloading power characteristic that peaks and then falls with increasing flow. read more →
A designation such as G 6.3 or G 2.5 (per ISO 21940-11) that specifies the permissible residual unbalance for a rotor as the product of specific unbalance and service speed; a lower G number means a finer balance and smoother running. read more →
The flow-and-pressure combination at which the fan converts the most shaft power into useful air power; selecting the duty at or just to the right of BEP gives stable operation and the lowest running cost. read more →
The tongue of the scroll nearest the impeller outlet that separates discharging air from recirculating air; its clearance influences pressure development, efficiency and blade-pass noise. read more →
Flow regulation by adding adjustable resistance — an outlet or inlet damper — which moves the operating point along the fan curve; simple and cheap, but it wastes energy as pressure drop across the damper. read more →
Effectively two impellers back-to-back on a common shaft drawing air through inlets on both sides, roughly doubling the flow of an equivalent SWSI wheel at the same pressure and speed. read more →
The standardised (AMCA) description of the bearing and drive configuration — for example an impeller overhung on the shaft with pedestal bearings, or belt- versus direct-driven — which dictates how the wheel is supported relative to the motor. read more →
The AMCA construction class (I, II, III, IV) defining the minimum pressure-and-outlet-velocity envelope a fan's build is designed to withstand; a higher class means heavier construction rated for more demanding duties. read more →
The manufacturer's characteristic plot of the pressure a fan develops versus volume flow at a fixed speed and density, usually shown with efficiency and power curves overlaid. read more →
Blades that lean toward the direction of rotation, moving a large volume at low speed and pressure but with a steeply rising (overloading) power curve and lower peak efficiency; the classic squirrel-cage wheel. read more →
The rotating assembly of blades, backplate and (optional) shroud that adds energy to the air; its blade type, diameter and speed set the fan's pressure, flow and efficiency. read more →
The inlet cone (inlet bell) guides air smoothly into the impeller eye; the radial overlap and running clearance between the cone and the wheel shroud strongly affect efficiency and leakage and must be set correctly on assembly. read more →
Adjustable radial vanes at the fan inlet that pre-swirl the incoming air in the direction of rotation, reducing the work done and shifting the fan curve to throttle flow more efficiently than a plain damper. read more →
The current international standard series for measurement and evaluation of machine vibration; it defines the vibration severity zones used to judge and accept a fan's running condition. read more →
The current international standard series for the mechanical balancing of rotors; Part 11 defines the balance quality grades used to specify residual unbalance for fan impellers. read more →
The single flow-and-pressure condition where the fan curve intersects the system curve; it is where the fan actually runs, which is not necessarily where it was selected. read more →
Blades that project straight out from the hub, tolerating high pressure, abrasive dust and material build-up at the expense of efficiency; the wheel of choice for material-handling and high-wear service. read more →
Construction that reduces the risk of a frictional or impact spark in a fan handling flammable atmospheres; AMCA defines Type A (all air-stream parts non-ferrous), Type B (non-ferrous impeller plus a non-ferrous rubbing ring at the shaft opening) and Type C (construction that prevents ferrous-to-ferrous contact between moving and stationary parts). read more →
The aerodynamic separation of airflow from the blade surface as the angle of attack becomes too steep at low flow, producing a dip or discontinuity in the fan curve, lost pressure and raised vibration. read more →
The potential (compressive) pressure a fan develops to overcome the frictional and dynamic resistance of ductwork, dampers and filters; it acts equally in all directions and is measured perpendicular to the airflow. read more →
An unstable, oscillating flow condition that occurs when a fan is driven far up the left (low-flow, high-pressure) side of its curve, causing periodic flow reversal, pressure pulsation, noise and mechanical stress. read more →
A centrifugal fan with one impeller drawing air through a single inlet eye; the standard configuration for most duties and the simplest to install and maintain. read more →
The plot of pressure a duct system requires versus volume flow; because losses are dominated by turbulent friction, required pressure rises roughly with the square of flow, giving a parabola through the origin. read more →
The peripheral velocity of the blade outer edge (pi times wheel diameter times rotational speed); it sets the maximum pressure a wheel can generate and is capped by blade material strength, especially at elevated temperature. read more →
The algebraic sum of static and velocity pressure, representing the total mechanical energy imparted to the air; fan total pressure equals the rise in total pressure from inlet to outlet. read more →
A VFD controls flow by varying motor speed; by the affinity (fan) laws, flow varies directly with speed, pressure with the square of speed and absorbed power with the cube of speed, making speed control the most energy-efficient method of turndown. read more →
The kinetic component of air pressure created by air in motion, always positive and acting in the direction of flow; it is a function of gas density and the square of velocity (VP is proportional to rho times V squared). read more →
The spiral-shaped fan housing that collects air leaving the impeller and converts part of its velocity pressure into static pressure as the cross-section expands toward the outlet. read more →
Flow, static, gas temperature, application — or attach a spec, GA drawing or a multi-fan schedule. Engineer to engineer.
ISO 9001:2015 quality system · performance-tested to IS 4894 / ISO 5801 / AMCA 210 method · witnessed FAT on request, at no cost.
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