FAQ
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%.
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.
It is 273 deg.C or 460 deg.F ( deg F may be specified in enquires from the USA). for example above you would correct 50mbar by multiplying by 273+50 / 273+20 this would give you an equivalent pressure of 55.1 mbar as your selection figure from standard catalogue data.
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 a 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.
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 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.
You must give the fan manufacturer all the relevent data and tell them how your design figures are calculated. At Fans & Blowers Ltd our technical sales dept will make all the neccessary corrections to give the correct fan selection.
Most industrial 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 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 dept. to ensure the fan is mechanically suitable.
- 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 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.
Yes but you must first make a correction for density difference just as you do for temperature. Standard fan performance data is usually as inlet volume and discharge pressure. If your 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 dept.
ATEX (ATmospheres EXplosibles) is a European directive, (EU ATEX Directive EN 94/9/EC) and mandatory from 01 July 2003. (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 a 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 fans will be designed, manufactured, tested & certified to F&B standard QA3-1000 with design data for Zone 1 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 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. Consult Fans & Blowers technical sales dept if you have such an application.
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.
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.
- Firstly a 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 fan and motor should be matched by the 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 blowers that have high impeller inertia.
- Closing a damper in the system during start up will give minimum starting time.
- Some fans may have motors rated for minimum power for reasons of economy, eg furnace fans where the motor is rated for the 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 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. (eg motor rated fuses)
Noise is largely a function of the amount of work a 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 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.
Can be due to overload, excessive ambient temperature, heat transmission/radiation from the fan, incorrect electrical connections, low supply voltage, faulty windings Seek advice of Fans & Blowers technical sales dept.
Can be due to worn bearings, out of balance impeller, poor installation, steelwork resonance, turbulent air entry conditions to the fan. Seek advice of Fans & Blowers Ltd Service dept.
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.
The first point to check is to make sure the fan is not larger than neccessary for your application. If you constantly run with partially closed damper then it wasting power. Check with Fans & Blowers Ltd technical sales dept for advice. We may be able to offer a more efficient fan and/or motor.
Loss of performance is usually due to a problem or change in the system if it is a deteriorating situation. Check for blockages, dirty filters, extra components added etc. If it is a problem from new, check system pressure drop calculations and blockages etc as above. Check that all relevent information on flow, pressure, density, electrical supply etc was given to the fan manufacturer. Check with Fans & Blowers Ltd technical sales dept for confirmation of correct fan selection and advice.
The simple answer is no. The fan will still be the same size running at the same speed doing the same job. It may be the case however that a fan has to be dampered back to keep within the motor full load amps. Under these circumstances a larger motor will enable the damper to be opened. Any fan will only do what the system allows it to do, within the limits of the fan capacity curve. A system has a unique pressure v flow characteristic just like a fan. The operating point will be where the system curve passes through the fan curve. Refer to Fans & Blowers technicla sales dept for advice.
If the 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 dept for advice.
There will frequently be an overlap of 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 dept for advice.
Fans & Blowers Ltd has extensive experience in the manufacture of 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.
Fans & Blowers Ltd can offer most of our fan range designed to VDI2263 'Explosion pressure shock resistant vessels' Please contact our technical sales dept.
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.
All our standard fans and blowers come colour coded. However, if you are ordering an bespoke fan/blower we can color it to your specifications.
To take a look at our standard colours please visit the product pages by clicking here.
For standard 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 think we cant deliver, so we will keep you informed every step of the development.