IS 4894 FOR CENTRIFUGAL FAN PDF

Sg; 5? The amendments issued to the previous edition of the standard have also been incorporated in this revision. The number of significant places retained in the rounded off value should be the same as that of the specified value in this standard. SCOPE 1. In the case of indirectly driven fans, the electric motor shall conform to the relevant Indian Standard, 1. The absolute pressure of the ambient atmosphere is the barometric pressure.

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Sg; 5? The amendments issued to the previous edition of the standard have also been incorporated in this revision. The number of significant places retained in the rounded off value should be the same as that of the specified value in this standard. SCOPE 1. In the case of indirectly driven fans, the electric motor shall conform to the relevant Indian Standard, 1. The absolute pressure of the ambient atmosphere is the barometric pressure.

It is positive when above and negative when below the ambi- ent pressure. It is always positive. Note — The difference in pressures is the mean pressure when facing tube reading is employed.

This is also commonly known as wheel diameter. This is normally shown in graphical fashion, following performance tests carried out in accordance with These are intended to prove general quali- ties and design of given type of fan. SIZES 3. Note — Nevertheless, fans made for other freque- ncies shall be considered to comply with the specifica- tion provided they do so in all other relevant respects.

Where the casing: contains members to be clamped against au exterior wall, these shall be capable of being sealed to prevent the ingress of rain-water at the point of attachment. The guards shall be securely attached and shall be adequately rigid to resist accidental contact with the blades. When the guards are in two pieces, positive locking arrangement to keep the two pieces together should be made.

Proper types of bearings should be used to ensure a reasonable amount of silent operation. IS ; A fan with protective electrical insulation may be of all-insulated construction or have either double insulation or reinforced insulation. In the case of fans for use on three-phase, two separate earthing terminals shall be provided. In the case of a double insulated fan, both basically insulated parts and live parts shall not be accessible to the standard test finger.

This requirement is applicable for all positions in the normal use. These insulat- ing materials are detailed in IS : J. Part of Motor or Rboulatob Class A Class E Tbmpbbatukh-Risb, "C Method OF Mbasu- BBMBNT 6 Change of resi- stance Change of resi- stance Insula- tion 3 60 60 Insula- tion 4 75 75 Class B Insula- tion 5 80 80 The temperature-rise shall not reach such a value that there is a risk of injury to any insulating material on adjacent parts of the regulator 40 40 40 Thermo- meter Thermo- meter 1 2 i] Insulated win- dings of motors ii Insulated wrin- dings, if any, of regulator with conti- nuous runn- ing on any contact iii Regulator resi- stance unit with conti- nuous runn- ing on any contact iv External surfa- ces likely to be touched during normal usage Note 1 — The thermocouples, if used, should be applied only to external surfaces which may be reached by an ordinary thermometer.

Never- theless, fans made to work in higher cooling air tem- peratures may be regarded as complying with this specification provided the temperature-rise values are reduced corresponding to the increase in cooling air temperature. Such fans shall be specially marked. However, if regulators are required, this shall be a matter of agreement between the purchaser and the supplier. IS : - 7. All metallic parts associated with it shall be protected from accidental contact.

The handle or knob shall be so designed that it does not become loose in use. In the case of inductance type regulator, it is essential that no portion of the inductive winding should remain permanently short-circuited in any of the running positions. Note — The need for specifying limits of noise levels acoustical of the fans is recognized.

However, it has not been found possible to specify these limits at present on account of: a dependency of these limits on the actual location of the fans, b lack of data on the acceptable noise levels for different applications, and c lack of agreed definition of noise level and method of evaluating the same.

The criterion of noise level may, therefore, be subject to an agreement between the manufac- turer and the purchaser. A system resistance line shall also be drawn, passing through the specified duty point such that the total or static pressure varies with the square of the inlet volume flow see Fig. The most probable operating point for the fan shall be at the intersection of the fan characteri- stic and the system resistance line.

The difference between the inlet volume flow at the intersection and the specified inlet volume flow that is, the duty point shall be recorded as the measure of departure of the fan from the specified perfor- mance.

This value shall fall within the range of specified tolerances. Note — The trade name, voltage and the size of the fan shall be marked on associated regulator. The Standard Mark on products covered by an Indian Standard conveys the assurance that they have been produced to comply with the requirements of that standard under a well-defined system of inspection, testing and quality control which is devised and super- vised by BIS and operated by the producer.

Standard marked products are also continuously checked by BIS for conformity to that standard as a further safeguard. Details of conditions under which a licence for the use of the Standard Mark may be granted to manufacturers or producers , may be obtained from the Bureau of Indian Standards.

TESTS If the fan is specified for two or more distinct rated voltages with three or more supply terminals, the tests shall be carried out at the most unfavourable voltage. In case of doubt, the tests shall be carried out at all voltages. While taking the current and watt read- ings during these tests, however, the voltage shall be maintained at the test voltage.

For routine and acceptance tests, instruments of class index 2 may be used. As type test, this test should preferably be done immediately after the temperature-rise test. The resistance measurement shall be made with a current of lOA with a dc voltage not exceeding 6V. The method of measurement of the speed of fan shall be such that the speed of the fan is not appreci- ably affected. This test shall be carried out with the guard if any, in position.

If more convenient, the flare may be remo- ved for the test. Such an addition shall then be regar- ded as a part of the fan. The inlet airway diameter D used in the computation shall be measured after- manufacture. The bore at. The openings - shall be flush with the duct and free from burrs and countersinks. The other limbs of the manometer shall be opened to the ambient atmosphere and the manometer reading shall be taken as equal to the average static pressure in the airway.

For Reynolds numbers of and above, the coeffi- cient of discharge is 0" and will cover the majority of fan tests. When the air flow, in cubic metres per hour, is numeri- cally less than 16 times the airway diameter in metres, then the coefficient of discharge shall be taken appropriate to the Reynolds number given in Table 2.

Intermediate values of d, may be obtained by linear interpolation. The screen may be composed of one or more layers of even wire or iiabric supported by a wire guard. The value to be adopted for the temperature of the cooling air during a test shall be the mean of the readings of the thermometers taken at equal intervals of time during the last quarter of the duration of the test. The value of r may be taken as 1 "4 for atmospheric air.

The copper losses shall be calculated on the corresponding current at the duty point of the fan. The stray load loss is assumed to be percent of the shaft power. The following additional information in respect of an electric centrifugal fan shall be supplied by the manufacturer on request: a Power factor, b Number of blades, c Type of regulator and number of running positions, d Glass of insulation, e Type of bearings, f Instructions for lubrication of bearings, g Condenser val ue in case of single-phase fans , and h Fan total efficiency.

The following information in respect of an electric centrifugal fan shall be supplied by the purchaser on request: a Size; b Electric supply details; c Air delivery at stated duty; d Nature of medium, air or other gases; e Atmospheric conditions; f Altitude of the place where the fan is to be installed; and g Whether guards are required.

A recommended sampling plan is given in Table 3. If the number of defectives found in the first sample is less than the rejection number, take a second sample of size indicated in col 3; and if the total number of defectives in the first and second sample put together is less than the rejection number, accept the lot, otherwise not.

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IS 4894: Centrifugal fans

Zujinn When the guards are in fkr pieces, positive centrifgal arrangement to keep the two pieces together should be made. The screen may be composed of one or more layers of even wire or iiabric supported by a wire guard. Such fans shall be specially marked. The absolute pressure of the ambient atmosphere is the barometric pressure. A system resistance line shall also be drawn, passing through the specified duty point such that the total or static pressure varies with the square of the inlet volume flow see Fig.

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IS 4894 FOR CENTRIFUGAL FAN PDF

Vudom The test voltage shall be applied as follows: The other limbs of the manometer shall be opened to the ambient atmosphere and the manometer reading shall be taken as equal to the average static pressure in the airway. This test shall be carried out with the guard if any, in position. The difference between the inlet volume centrifugaal at the intersection and the specified inlet volume flow that is, the duty point shall be cebtrifugal as the measure of departure of the fan from the specified perfor- mance. IS Centrifugal fans When the air flow, in cubic metres per hour, is numeri- cally less than 16 times the airway diameter in metres, then the coefficient of discharge shall be taken appropriate to the Reynolds number given in Table 2. It is positive when above and negative when below the ambi- ent pressure.

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