Making the system safe
Fans are made to many different arrangements and cover a variety of sizes and impeller types. Properly installed, run and maintained, they assist in the creation of better living conditions, cool other equipment, provide essential air for combustion, convey materials, and efficiently carry out many other functions.
All fans have moving parts which may require guarding and access doors to duct systems will also be needed. For further details of guards and doors, refer to Chapter 16, Sections 16.2 and 16.3.
Excessive noise can be a health hazard. The sound pressure level at any given location is dependent on the effect of all noise generating equipment and the acoustic environment within the vicinity of the reference point, the fan being only one of the contributing sources. It is, therefore, difficult to predict the sound level without a complete survey of all equipment, orientation of each sound source, acoustical characteristics of the structure, and distances involved to each noise source.
Acoustical engineering services should be employed to determine compliance with noise regulations and to make recommendations on any necessary attenuation devices.
Before putting any fan into operation the following operations should be completed.
1. Cut out primary and secondary power source.
2. Make sure the foundation or mounting arrangement and the duct connections are adequately designed in accordance with recognised acceptable engineering practices.
3. Check and tighten all holding down bolts.
4. Spin impeller to see if rotation is free and does not bind or rub.
5. Inspect impeller to see if it is the proper handing for the fan design.
6. Check all set screws and tighten if necessary.
7. Check vee drive or coupling for alignment — use recommended belt tension.
8. Check vee drive for proper pulley selection and make sure they are not reversed or the fan could run to excessive speeds as well as overloading the motor.
9. Make certain there is no foreign loose material in ductwork leading to and from fan or in fan itself.
10. Properly secure all safety guards.
11. Check security, correct alignment, and fixings of flexible connectors.
12. Secure all access doors to fan and ductwork.
13. Close any inlet or outlet fan dampers.
14. Switch on electrical supply and allow fan to reach full speed.
15. Progressively open dampers, making certain the system continues to function satisfactorily and that motor does not overload.
16. Check carefully for:
— Correct impeller rotation (shown by rotation arrow on fan casing).
— Excessive vibration.
— Unusual noise.
If any problem is indicated switch off immediately. Cut out the electrical supply, check carefully for the cause of the trouble, and correct as necessary.
Even if the fan appears to be operating satisfactorily, shut down after a brief period and recheck items 3 to 12 as the initial start-up may have relieved tightness of bolts and set screws, again ensuring electrical supply is cut out before attempting other checks.
The fan may now be put into operation, but during the first eight hours of running it should be periodically observed and checked for excessive vibration and noise. At the same time checks should be made on motor input current and motor temperatures to ensure that they do not exceed manufacturer’s recommendations.
After eight hours of satisfactory operation, the fan should be shut down and the power cut out to check the following items and adjust if necessary. .
1. All set screws and hold down bolts including guard fixings.
2. Drive coupling alignment.
3. Vee drive alignment.
4. Vee drive belt tensions should be readjusted to recommended tension.
5. Security of flexible connections.
Every fan must be provided with a disconnect switch which will allow it to be isolated completely from the electrical supply.
Most roof-mounted fans and many others are started by remote switches or push-buttons, by interlocks with other equipment, or by automatic controls. In these cases a disconnect switch must be provided close to the fan so that maintenance personnel can “positively” cut off the power when working on the fan. See Figure 18.1.
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Figure 18.1 Remote switch — left; disconnect switch — right |
In some installations other equipment, such as gas burners, may be interlocked with the fans so that disconnecting the fan will automatically shut off the burner or other device. Maintenance on systems of this type should be performed only under the supervision of competent technical staff.
Fans which are used to move anything other than clean air at normal temperatures (-40°C to +75°C) may require special precautions to ensure safe operation. Explosive or toxic fumes or gases, transported solids, high temperatures, and corrosive contaminants will present special hazards which must be carefully considered. All national and local codes should be reviewed together with any applicable industry standards. The manufacturer’s recommendations for the specific application should be closely followed.
When the system will handle explosive or inflammable fumes or gases, fans of spark-resistant construction should be used. The manufacturer should be consulted when specifying fans for this use. There is now a draft European Standard prEN 14986 to meet the requirements of the ATEX Directive.
If the fan is handling toxic or explosive fumes — even in traces
— care must be taken to ensure that fumes have not collected in areas which require access by workmen. Concentrations of fumes can collect in “air trap" areas, particularly when a system is shut down.
Fans with radial or paddle impellers are specially designed to allow the fan to handle a specific type of material without excessive accumulation of material on the fan wheel. To ensure satisfactory operation it is essential to observe the manufacturer’s limits concerning the type of material to be handled by the fan.
Fan ratings and maximum speed limits are based on the use of air at 20°C. At temperatures above the normal range (over say 150°C) a reduction must be made in the maximum speed limit. Information on this and on other precautions to be taken for high temperature applications may be obtained from the manufacturer.
Corrosive contaminants can be formed when moisture combines with an active airborne chemical. Unprotected fans subjected to corrosive attack will eventually fail, but suitable protective coatings or material used in the fan construction will resist corrosion. Even protected fans must be regularly inspected to ensure that the protection remains effective.
Posted in Fans Ventilation A Practical Guide