A-A-50548
larger than 57 inches (1448 mm) in fan diameter shall be easily converted at angles of 45 degrees. When specified (see 7.2), a threaded drain connection to accommodate a 1 inch (25.4 mm) or 3/4-inch (19.1 mm) diameter standard pipe, as specified (see 7.2). Standard pipe shall be located at the lowest point in the scroll. When specified (see 7.2), a flush type access door shall be installed on the fan scroll and held by quick-release clamps on type II fans. Inlet and outlet duct connections shall be flanged.
TABLE I. Housing gages.
|
Nominal fan diameter (inches) |
Sides and Scroll |
|
12 (305 mm) up to 16 (406 mm) |
16 gage |
|
16 (406 mm up to 24 (610 mm) |
14 gage |
|
24 (610 mm) up to 72 (1829 mm) |
12 gage |
|
72 (1829) up to 132 (3353 mm) |
10 gage |
3.6.5 Motor. The motor shall conform to NEMA MG 1, and shall be capable of continuous operation when driving the fan at rated conditions, and may be single or multiple-speed unless one of these is definitely specified (see 7.2). Features of bearings, enclosure, and electrical characteristics shall be as specified (see 7.2). When specified (see 7.2), and across-the-line part-wind wye-delta or autotransformer shall be supplied. When specified (see 7.2), the motor shall be open drip proof, totally enclosed, or explosion proof.
3.6.5.1 Direct drive. When a direct drive is specified (see 7.2), the fan wheel shall be mounted on the motor shaft or driven through a suitable coupling by the motor. The motor shall be aligned to minimize drive line vibration. When specified (see 7.2), the assembly shall be mounted on resilient vibration isolators.
3.6.5.2 V-belt drive. The fans shall be driven by means of single or multiple V-belts. Quantity and cross-sectional size of the belts shall be determined by the motor horsepower rating corrected to the service and arc-of-contact factors. For the motor location specified, a standard belt length shall be used to the nearest, but not less than the recommended, motor and fan shaft center distance. Sheave pitch diameters shall be as specified by the manufacturer for the speed ratio and fan speed required. When specified (see 7.2), sheaves shall be of a variable pitch type. The motor shall be solidly mounted to a suitable base which shall provide for belt tension adjustment and for anchorage to the fan foundation. All exposed belt-driven fans shall have safety guards that conform to ANSI B15.1 and adjustable motor mounts for belt tension adjustment and belt replacement. V-belts shall conform to ZZ-B-225. Sheaves shall conform to NEMA MG 1 for minimum electric motor sheave diameter for a given horsepower motor. Motor sheaves shall be of the adjustable pitch type which provides a 20 percent speed variation, selected so that the specified capacity will be delivered with sheaves at approximately mid position. V-belt drives shall be selected for continuous duty in accordance with RMA Engineering Standards for Multiple V-Belt Drives with a service factor of 1.5.
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