FAQ

Below is a list of frequently asked questions. If you do not find the answer to your enquiry please give us a ring on 01278 784 004 and we will be able to help.

What is Standard Air

You will find many different figures for standard air but at Fans & Blowers we use a figure of 1.2kg/m3 at sea level at a temperature of 20 deg.C and RH of 65%.

How do I correct standard catalogue fan data to my site conditions?

You must correct for density differences. Eg if you require a pressure of 50mbar at 100 deg C you must correct this back to standard air by ratio of absolute temperatures.

What is absolute temperature?

A reference level based on lowest theoretically possible temperature.

On the Celcius scale (C) absolute zero is minus 273 K. (K = Kelvin and should not be referred to as degrees Kelvin.

Likewise on the Fahrenheit scale (F) absolute zero is minus 463 R. (R = Rankine)

These are rounded figures acceptable for engineering use.

These absolute figure are used to correct gas densities for temperatures other than standard atmospheric.

Eg. A pressure of 50 mBar at 200 C becomes 50 x (273+200) / (273+20) = 80.7 mBar at 20C.

This is the pressure to use for fan selection off a standard chart at 20C.

Mass flow rates may also require similar corrections.

How does electrical frequency affect my industrial fan selection?

This is a common trap that many people fall in to. Standard catalogue data (European) would normally be at 50Hz frequency. This means that say 2 pole motors run at nominal 2900 rpm or 4 pole at 1450 rpm. On a 60 Hz supply it would run at nominal 3500rpm and 1750 rpm respectively. (actual full load speeds vary by a few %) If you purchase an industrial centrifugal fan designed to give a specified duty at a 50Hz speed but use it on a 60Hz supply it will run faster therefore giving more flow, pressure and critically, more power, probably overloading the motor. It is essential that the electrical supply frequency is specified to the fan supplier.

Fan terminology such as fans, blowers, exhausters, boosters etc confuses me, what does it all mean?

The simple answer is that it is just terminology that means different things to different people. However in general terms a blower would usually be a relatively low flow high pressure industrial centrifugal fan. Positive displacement machines, eg Rootes type are referred to as blowers and they work on a different principle to a centrifugal fan. An exhauster operates on a suction duty rather than blowing. A booster would normally be found in a closed system boosting from a pressure in excess of or less than atmosphere at its inlet to a higher pressure at its outlet. If you have any doubt contact Fans & Blowers Ltd Technical Sales dept.

What if my industrial fan or blower requirements have all sorts of differences, eg Altitude, temperature, humidity, gas other than air etc.

You must give the industrial fan manufacturer all the relevant data and tell them how your design figures are calculated. At Fans & Blowers Ltd our technical sales department will make all the necessary corrections to give the correct industrial fan selection.

Can I just speed my industrial fan up to make it more powerful?

Most industrial fan motors these days are suitable for speed increase by invertor control. (But beware motors for hazardous areas may not be certified for use with speed control.) However you should be aware of the industrial fan laws because you will get an increase in flow, pressure and power and could overload your motor. You will also need to contact Fans & Blowers Ltd Technical Sales department to ensure the centrifugal fan is mechanically suitable.

So what are these industrial fan laws?

  • Speed change:- flow varies directly proportional, pressure as speed squared, power as speed cubed.
  • For example double your speed and you will get twice the flow and four times the pressure but take  eight times the power!
  • Density change:- Flow (volume) will remain constant (but not mass which will vary directly proportional)
  • Pressure and power will vary directly proportional to density.
  • There are other industrial fan laws based on size change or combination of all, but speed and density are the ones that the fan purchaser will be mainly involved in.

If my centrifugal fan is to operate on suction can I use standard catalogue data?

Yes but you must first make a correction for density difference just as you do for temperature. Standard centrifugal industrial fan performance data is usually as inlet volume and discharge pressure. If your industrial fan operates under suction conditions the density at the inlet will be less than at test conditions. The site data will need correcting by the ratio of absolute densities, consult Fans & Blowers technical sales department.

What is an ATEX certified industrial fan?

ATEX (ATmospheres EXplosibles) is a European directive, (EU ATEX Directive EN 94/9/EC) and mandatory from 01 July 2003 becoming 2014/34/EU on 20th April 2016. (note a directive is not a specification) It covers sites handling hazardous gas and/or dust which are subected to expert hazard assessment and zoned according to gas/dust type and degree of hazard. Equipment to be installed in an area that has been so designated must have equipment that is certified as being suitable for the relevent zoning and covers both electrical and mechanical equipment. Zones for gases will be 0, 1 or 2. Dust will be 20, 21 or 22 and the relative fan category will be 1, 2 or 3. Hazardous areas can be inside or outside the fan or both and a mixture of Zones, eg. Zone 21 inside, Zone 2 outside etc. Fans & Blowers Ltd can supply an ATEX Approved industrial fan for most applications that will conform to a hazardous area specification and will carry the εx label appropriate to its zone rating. For Zone 1 & 2 the industrial fans will be designed, manufactured, tested & certified to F&B standard QA3-1000 with design data for Zone 1 centrifugal fans being lodged with a 'Notified Body' and marked with Technical file ref. SIRA-04-ATEXT-334. Note that our ATEX fans are not just standard centrifugal fans with a non ferrous rubbing ring and a label!! They have fully documented hazard assessments and design, manufacturing, inspection & test procedures including an extended test run to ensure compliance with 'T' ratings. Appropriate design standards, machinery directives etc are listed in the documentation and labelling. We use standard BS EN 14986:2017 'Design of fans for use in potentially explosive atmospheres' for all our ATEX fans.

Consult Fans & Blowers technical sales department if you have such an application.

What is the difference between an axial flow and a centrifugal fan?

An axial flow fan moves its air along its axis. They are usually simple fans, impeller mounted on a motor shaft and contained in a circular casing for mounting directly into a run of ducting. Ideal for a low pressure, low temperature, low cost applications although special variations are available. A centrifugal fan takes the air in at its centre and turns through 90 degrees to discharge radially. The centrifugal fan is the 'all singing all dancing' fan as it can develop high pressures and in its different forms handle high temperatures, high dust burdens, be gas tight construction, fabricated in a wide range of materials etc.

What information must I tell the fan manufacturer when I am looking for a quotation.

Minimum basic data needed is flow and pressure. Additional data required is:-

  • Type of gas (eg air, methane, nitrogen etc) and its density if possible.
  • Any erosive and or corrosive elements in gas stream.
  • Temperature
  • Altitude
  • Is flow actual or mass (eg m3/hr or kg/hr etc)
  • Is pressure at discharge or suction or combination of both.
  • Is performance calculated at standard density conditions or actual site density.
  • Preference for direct or indirect drive.
  • Electrical supply.
  • Site conditions ( eg indoors/outdoors, dusty, hazardous etc)
  • Any specific requirements for materials, construction standards, motor standards etc.
  • Noise level requirements.
  • General description of application to assist the fan manufacturer to use their expertise in selecting the best fan for the job. ( eg Ventilation, Combustion air, pneumatic conveying, material handling etc)
  • Consult Fans & Blowers Ltd Technical sales dept for their assistance.
  • We cannot be experts in all applications but we have a combined wealth of experience in many.

Why am I having problems starting my centrifugal fan?

  • Firstly an industrial fan must never be run without a back pressure (ie do not 'bench run' without its normal system of ducting, valves, filters etc connected) It will extend the run up time and will probably overload and burn out the motor.
  • The centrifugal fan and motor should be matched by the industrial fan manufacturer to give a run up time that is within the motor manufacturers limits, the purchaser in turn must ensure that the switchgear provided is adequate for the starting current and time.
  • Run up time can be critical in the case of hazardous area motors and may require the kw rating to be above that normally required to cover actual fan power requirements. This is especially a problem with high pressure low flow centrifugal blowers that have high impeller inertia.
  • Closing a damper in the system during start up will give minimum starting time.
  • Some industrial fans may have motors rated for minimum power for reasons of economy, e.g. furnace fans where the motor is rated for the centrifugal fan power at temperature only.
  • Cold start by closing damper or at reduced speed.
  • Many motors are dual voltage so ensuring motor is connected at the terminal box correctly is critical.
  • Ensure that there is no excessive voltage drop in electric supply.
  • Ensure industrial fan is running in correct rotation.
  • Direct on line starting is usually preferable for industrial fans but the high starting currents can cause problems with local supply capacity.
  • Limited current switchgear is available but with the penalty of extended run up times.
  • Fuses and overloads must be rated not only for the degree of current but its duration. (e.g. motor rated fuses)

How noisy will my industrial fan be?

Noise is largely a function of the amount of work an industrial fan is doing and its efficiency and therefore can be anything from 'very quiet' to 'very noisy' ( this is subjective and quite meaningless terminology) Speed and blade type/quantity also have a bearing. Noise will emanate from various sources, inlet/outlet, casing breakout and motor/drive noise. A centrifugal fan with an inlet or outlet open to atmosphere may require a silencer. If casing breakout is excessive it may require a heavier casing, lagging or complete enclosure. Motor noise may require a motor silencer or complete enclosure. Your enquiry must stipulate noise criteria required and description of its location and where noise emanating from the fan will be a problem. ie. is it around the fan or in-duct or both.

My centrifugal fan motor is getting hot

Can be due to overload, excessive ambient temperature, heat transmission/radiation from the industrial fan, incorrect electrical connections, low supply voltage, faulty windings Seek advice of Fans & Blowers technical sales department.

My industrial fan is vibrating

Can be due to worn bearings, out of balance impeller, poor installation, steelwork resonance, turbulent air entry conditions to the centrifugal fan. Seek advice of Fans & Blowers Ltd Service department.

How often should I service my industrial fan?

Refer to your Operating & Maintenance instructions for your fan, consult with Fans & Blowers Ltd Service dept or speak with our sales department for service contract.

Can I reduce the cost of running my centrifugal fan?

The first point to check is to make sure the industrial fan is not larger than necessary for your application. If you constantly run with partially closed dampers then it wasting power. Check with Fans & Blowers Ltd technical sales department for advice. We may be able to offer a more efficient centrifugal fan and/or motor.

If I put a bigger motor on my industrial fan will it do more work

The simple answer is no. The industrial fan will still be the same size running at the same speed doing the same job. It may be the case however that an industrial fan has to be dampened back to keep within the motor full load amps. Under these circumstances a larger motor will enable the damper to be opened. Any industrial fan will only do what the system allows it to do, within the limits of the centrifugall fan capacity curve. A system has a unique pressure vs flow characteristic just like a centrifugal fan. The operating point will be where the system curve passes through the fan curve. Refer to Fans & Blowers technical sales department for advice.

I have a centrifugal fan, can you tell me what flow and pressure it will give me

If the industrial fan type is known to us then we can produce a curve but probably not be able to tell you precisely its operating point. See FAQ above. Refer to Fans & Blowers technical sales department for advice.

Why are there so many different types of industrial fans, several seem to do the same duty

There will frequently be an overlap of industrial fans from a volume/pressure point of view. However the application will usually determine which one is right for the job. It may be dirty air which will require a different blade type to one for clean air. It may require a flat curve at the duty point or a steeply rising curve. Other considerations will also be taken into account to ensure the correct fan is selected. Consult with Fans & Blowers technical sales department for advice.

What if I need a gas tight centrifugal fan

Fans & Blowers Ltd has extensive experience in the manufacture of industrial gas tight fans. Gas tight versions of most of our fan range are available. Type of seals and degree of gas tightness will be selected according to application and can also be at elevated temperatures, with gases from air to hydrogen. Most of our gas boosters are manufactured to BS8487:2007+A1:2013

My system has an explosion hazard, what can you offer?

Fans & Blowers Ltd can offer most of our industrial fan range designed to VDI2263 'Explosion pressure shock resistant vessels' Please contact our technical sales department.

Do you offer bespoke products?

Here at Fans & Blowers we can design, make and install any bespoke product to fit your requirements. We will even come an do an evaluation of required use.

This may be a silly question but what colours do they come in?

All our standard industrial fans and blowers come colour coded. However, if you are ordering a bespoke industrial fan or blower we can colour it to your specifications. To take a look at our standard colours please visit the product pages by clicking here.

What is your lead-time?

For standard industrial fans/blowers we generally have a lead time of 2-3 weeks depending on how busy we are. Bespoke products generally have a lead time of 2-3 months including the design dependent on the complexity. We will never promise what we can’t deliver, so we will keep you informed through every step of the development of your Industrial fan.