Technical Library Axial Flow Fans

Axial Flow Fans - Adjustable Pitch



This section of the site details the performances of a wide range of axial flow fan types as follows:-

Duct Mounted Axial Fans

    • AP Series - direct driven
    • APV Series - direct driven, vertical mounted
    • APS Series - direct driven, smoke-spill
    • APB Series - belt-driven
    • BFA Series - bifurcated, direct driven

Wall Mounted Fans

    • SQ Series - square plate, direct drive

Axial Roof Units

    • RDE Series - downflow cowl, exhaust
    • RDS Series - downflow cowl, supply
    • RVE Series - vertical discharge
    • RSS Series - vertical discharge, smoke-spill
    • HC Series - high capacity, vertical discharge
    • SS Series - smoke-spill
The above fans range in diameter from 315mm to 2000mm.

Test standards

The International Standards Organisation (ISO) achieved a standardised fan test code with the publication of ISO5801:1997. This Standard replaces BS848:Part 1, 1980 upon which it was based.

Fan performances for the Elta 1000 Series diameter have been aerodynamically tested to BS848:Part 1, 1980 and the Elta 1400 and 2000 Series to ISO5801:1997. All three series have been tested to BS848:Part 2, 1985 for sound performance.

The main difference between the above Standards and those they replaced, is the installation Types A, B, C and D such that, if a fan unit is designed for use in any one of these arrangements, the variation in performance should be established and shown.

Test Standard

Both BS848:Part 1, 1980 and ISO5801:1997 reflect the latest understanding of measuring techniques and accuracy in fan performance testing.

If the same fans were tested to pre-1980 air flow and noise Standards and then to the latest Standards, different performances would be obtained. The results from the later Standards give differences of as much as:-

  • -5% in volume
  • -10% in pressure
  • -5% in efficiency
  • +2 to 6dB in noise
These differences should be borne in mind when making comparisons of fans tested to the different Standards, as they are the result of the test method and not the product.


The achieved fan performances can differ from the test performances shown on the subsequent pages due to two main effects:- 

a)   The encroachment of irregular or abrupt changes within the system close to the fan. If good design practice is followed, then the fan will receive nearly uniform air into its inlet and discharge its air flow in a nearly ideal pattern. If this is achieved the fan will perform to its expected level. 

Refererence to the Do's and Don’t's listed on this website or Section O of the Fans by Fantech atalogue will assist in avoiding pitfalls. The advice in "Do's and Don'ts" applies to the application of all fans, not just axial flow fans.

b)   Changes to the internal elements of the fan: e.g. large junction boxes on motors, belt drive stacks or excessive blade tip clearances.

    Operating Range

Tests were conducted to assess these effects and the generalised impact is shown below for fan selections made within the normal operating region over a wide blade-angle range.

Forms of running

The main series of tests were conducted on Form B units and comparative tests were carried out on Form A units. Resultant performance differences occur mainly on the outlet side of the fan, as correct practice should result in the presence of a duct or inlet cone on the fan inlet.

We supply fans to Form B running unless Form A is requested at the time of the order.

Forms of running

Dowm Stream Guide Vanes

A normal axial flow fan, whilst being very economical and compact, imparts motion to the air in an axial and rotational direction. The rotating component is usually called ‘swirl’. The swirl component eventually dissipates, but by using Down Stream Guide Vanes (DSGV) it can be converted to more useful static pressure. Static pressure increases of 10%-25% can be achieved with DSGVs, thus giving an increase in efficiency. As the work is done after the air leaves the fan, DSGVs do not require any additional fan power. They are most effective at pitch angles over 20° and produce small increase in sound levels of 1-2dB.

Multi-stage axial flow fans

Multi-stage axial fans with contra-rotating impellers can be supplied up to 1400mm diameter.

A two-stage assembly develops approximately 2.4 times the pressure developed by a single-stage fan and increases the overall sound level by 8 to 10 dB.

To select a contra-rotating axial fan from the curves in this catalogue, divide the specified static pressure by 2.4 and then select as though it were a single-stage unit. The kW derived is for one stage only and the noise level will be 8 to 10 dB higher than the single-stage fan.

NOTE: Reference should be made to Fantech for complete selections of these fan arrangements. Alternatively selections can be made using our Fans by Fantech product selection CD.




The blades have been designed for optimal performance, for both aerodynamic needs as well as noise characteristics. They are available in a range of materials as shown below:-

Impeller Ranges

Range of diameters


No of blades


Hub Dia mm



315 to 900   5 or 10   150   GRP, Nylon, Alum. Or Anti-static GRP  
560 to 1000   7 or 14   250   GRP, Nylon, Alum. Or Anti-static GRP  
800 to 1250   3 or 6   255   GRP, Nylon, Alum. Or Anti-static GRP  
800 to 1400   3, 6, 9 or 12   350   GRP, Nylon, Alum. Or Anti-static GRP  
1000 to 1800   3, 6 or 9   400   GRP or Aluminium  
1250 to 2000   3, 6, 9 or 12   550   GRP or Aluminium  

The stress limits of the blades vary from one material to another and simplified criteria are incorporated on the curves. However, if selecting fans using our interactive product selection CD, you may find solutions with higher pitch angles are chosen; these selections are quite acceptable.

It should be noted that, as we are constantly reviewing the materials we use, these limits may be extended.


All hubs use Fantech TECH-LOCK® taper bushes as standard with one exception. The bush ensures ease of fitting and removal of the impeller from the motor shaft should adjustment of the pitch angle, cleaning or repair of the impeller prove necessary. The exception is for bores above 65mm and 85mm diameter for the 400mm and 550mm diameter hubs respectively. In these cases we supply impellers with simple through-bores.


All impellers are assembled using high-tensile, zinc-plated set screws and self-locking nuts.


Right and left-hand blades are available enabling the selection of contra-rotating or multi-stage axial flow fans up to 1400mm diameter. If contra-rotating fans of a larger diameter are required please refer to our sales department.

Standard Material

GRP blades will be supplied for normal clean ventilation applications as standard except where otherwise specified, or where local regulations prohibit their use. 


The balance of all impellers is carefully checked to ensure vibration-free running.

Fully-adjustable Blades

All impeller pitch-angles are fully adjustable. For the Elta Range, up to size 1400, the required blade angles are set on jigs but for sizes up to 100, may also be set utilising the graduated scale at the root of each blade. For the Elta 2000 Range pitch angle setting is by protractor.




All axial fan casings are rolled and flanged from heavy-gauge mild steel and hot-dip galvanised after manufacture. The standard casings enclose the impeller and motor completely and weatherproof external terminal boxes are standard.

The motor is wired into the external terminal box through flexible terminal weatherproof conduit and a separate earthing screw is provided.

An inspection hatch is standard on fans 1000mm diameter and over, a 50 mm sight hole is fitted on smaller fans. An inspection hatch is available in the smaller fans on request.

Flameproof or increased-safety motors are not normally wired to the outside of the case so the client can connect directly to the terminal box in accordance with the requirements for the particular hazardous zone.

Direct-drive - AP Series (315 to 2000 mm diameter)

Direct-drive - AP Series (315 to 2000 mm diameter)

The entire range can be provided in a wide choice of speeds to meet an extensive range of performances and applications. If a speed or duty you require is not shown please contact our sales engineers for assistance. In general, all flameproof or special application motors can be fitted if required.

Direct-drive - APV Series (315 to 2000 mm diameter)

The full range of sizes and speeds can be provided as direct-drive APV units for applications where the fan must be installed vertically. The casing is designed with integral outriggers to facilitate vertical mounting.

Direct-drive - APS Series (315 to 2000 mm diameter)

For smoke-spill applications we can supply fans up to 2000mm diameter fully tested to meet the Australian Standards AS/NZS1668.1:1998 and AS4429:1999. See below for more information.

Belt-drive - APB Series (315 to 2000 mm diameter) 

The full range of sizes and speeds can be supplied as belt-driven APB units for applications where the motor must be out of the air stream.

When selecting these fans allowance for the additional pressure loss caused by the drive arrangement must be taken into account as follows:-
  • Open belts: no extra pressure loss
  • Sealed belt guard: add 5% to the design pressure.

Belt-drive - APB Series (315 to 2000 mm diameter)

Bifurcated - BFA Series (400 to 1250 mm diameter)

Bifurcated - BFA Series (400 to 1250 mm diameter)

This range is available in a wide choice of speeds. Bifurcated axial flow BFA fans are designed for handling toxic, noxious, abrasive and hot gases and can be used as an alternative to the APB belt-driven range.

The maximum air temperature the standard bifurcated fan can handle continuously, and without special treatment to the impeller and motor, is 100°C for an aluminium impeller or 70°C for GRP.

Bifurcated fans can be specially built to accommodate temperatures of up to 200°C continuous for sizes up to 1250mm and 250°C up to sizes 630mm.

For this type of application it is essential the fan be mounted in normal ambient conditions, that the central motor tunnel be aligned vertically and that the motor have Class F insulation and equivalent lubrication of the bearings.

Refer to us if the fans are to handle higher temperatures or the motor tunnel is not vertical.

When selecting these fans the following allowances must be made to the duty to compensate for the central shroud:-

    Sizes 400 to 560 - 1.0 × pdF
    Sizes 630 to 1250 - 0.7 × pdF

Square Plate - SQ Series (315 to 1250 mm diameter)

This range is available in a wide choice of speeds. All square-plate fans, irrespective of the direction of the air flow, incorporate a bell-mouth entry; the direction of air flow must be nominated at the time of order.

Generally all flameproof or increased safety motors can be fitted if required.

When selecting these fans installations Type A or B must be used.

The square plates are of heavy-gauge steel with a bell-mouth entry and are hot dip galvanised after manufacture. Electrical supply will normally be taken directly to the motor terminal by the installing Contractor.

See Wall, Window & Celing Mounted fans section for alternative selections of size 315 to 800 diameter square plate fans.


Square Plate - SQ Series (315 to 1250 mm diameter)


All galvanising of axial flow fan products is to AS1650 and is the standard finish on the fans detailed above and their accessories.



New Generation Series - RDE, RDS, RVE & RSS (315 to 1250 mm diameter)


New Generation Series - RDE, RDS, RVE & RSS (315 to 1250 mm diameter)

These are available in both vertical and down flow configurations and can be supplied in a wide range of speeds. The hot dip galvanised heavy-gauge steel base incorporates a bell-mouth entry to optimise the air flow. Down flow top caps are generally plastic and vertical discharge cowls are of fibreglass or steel. In general, all flameproof or special application motors can be fitted if required.

High Capacity and Smoke-Spill Series - HC & SS (500 to 1800 mm diameter)

These are for vertical discharge applications only, have a hot dip galvanised steel construction and can be supplied in a wide range of speeds. In general, all flameproof or special application motors can be fitted if required.

The SS Series is specifically designed for smoke-spill applications, see notes below for more comprehensive information on smoke-spill Standards and the range available.

When selecting any of the above fans, use Type A Installation or, more accurately, use our interactive CD.


High Capacity and Smoke-Spill Series - HC & SS (500 to 1800 mm diameter)


Smoke-spill fans have to be tested to Standard AS4429:1999 to conform with the new requirements of AS/NZS1668.1:1998. To meet the Standards Fantech conducted an extensive series of tests covering both air flow and temperature. The air flow tests for sizes 315mm to 1000mm diameter conformed to BS848:Part 1, 1980 and to ISO5801 for sizes 1.0m to 2.0m. The temperature tests were conducted in accordance with AS4429:1999, although the 300°C tests were extended from 0.5 hours to 2 hours to ensure we met the needs of most of our export markets.

The outcome of the series of tests is that we can supply fans ranging in diameter from 315mm to 2000mm at speeds as high as 2 pole depending on size and, for both 50 and 60Hz supply that fully comply with the Standards in all respects.

The following conditions can be met:-

  • 200ºC for two hours
  • 200ºC for four hours
  • 250ºC for four hours
  • 280ºC for 0.5 hours
  • 300ºC for 0.5 hours
  • 300ºC for two hours

Discharge damper fail-open latching

An additional requirement of the Standards relates to the function of the discharge dampers in unsprinklered buildings. Fantech has met the requirements with two designs, the first being a manual release type requiring manual closing after the fan has been run. These may be used for dedicated smoke spill fans. The second design, an electro-mechanical arrangement, permits the shutters to close automatically after the fan stops. These are recommended for use on dual-purpose ventilation/smoke-spill fans. Fantech has provisional patents for both designs.

For advice on Smoke-Spill wiring requirements, refer to the above Standard.

Contact our Sales Engineers for additional information.



Our CD is an interactive product selection program encompassing the following features:-

  • a fan selection program
  • an attenuator selection program
  • an acoustic analysis system
  • enables drawings to be downloaded through dwg/dxf files and
  • easily updated with the latest data from our website.
To obtain a copy of our CD, contact one of our Sales Offices.



Air flow direction can be reversed on fans fitted with three-phase motors by simply reversing the direction of rotation.

The impact on performance in reverse rotation approximates to:-

    Air flow reduction -30%
    Pressure reduction -55%
    Power reduction -25%



Equal volume flow in both directions can be achieved by blade reversal procedures carried out when the impeller is being assembled.

The impact on performance when compared to standard performance approximates to:-

    Air flow reduction -15%
    Pressure reduction -25%
    Power reduction -20%



Impellers installed for O.E.M. applications are submitted to the vibration, cyclic torques and temperature cycles that prevail within the item of equipment. It can therefore be misleading to state maximum conditions unless the full operating environment is known, as all the above points can be inter-related.

The table below should be used as a guide only. For accurate figures use our CD.

Blade Material


Temperature Range


Limiting Tip Speed**

Elta 1000 Impeller*             
    Aluminium    -40°C to +200°C    115m/s   
    GRP    -40°C to +70°C    95m/s   
    Nylon    -40°C to +100°C    115m/s   
    Anti-static GRP    -40°C to +70°C    95m/s   
Elta 1400 & 2000 Impeller#             
    Aluminium    -40°C to +200°C    105m/s   
    GRP    -40°C to +70°C    95m/s   
    Anti-static GRP***    -40°C to +70°C    95m/s   

*Up to 1000mm diameter 
**Applicable to 20°C

***1400 Series only 
#1400 Series = 800mm to 1400mm; 2000 Series = 1250mm to 2000mm



The performance curves on pages C-9/105 of the Fans By Fantech 2004 catalogue show the total in-duct sound power levels for the outlet side of the fan. Intermediate values may be obtained by interpolation; the data is based upon tests to BS848:Part 2, 1985.

More detailed information may be obtained by referring to the Sound Data table applicable to the particular fan. 

To use the table:-

  • The performance zone applicable to the fan duty is obtained from the large background numbering on the performance graph.
  • The correction values are then read from the relevant zone in the Sound Data table. The total and octave band sound power levels for inlet and outlet side, in-duct and free field, are obtained by adding or subtracting the applicable values from the total sound power level obtained from the performance curve.
  • Total sound pressure levels at 3m and spherical radiation (re 20mPa) are obtained by subtracting 21dB from the applicable sound power levels.
  • The “A” weighted sound pressure (dB(A)) is obtained by subtracting the dB(A) value listed in the table from the total sound pressure.

Elta Group