top of page
Amarillo Gear Drives

Drop-In for Marley - Single Reduction "A" Series Gear Drive

The Single Reduction “A” Series Gear Drives for cooling towers from Amarillo Gear Company are designed as direct replacements for the Marley® right angle gear boxes. Since there are no differences in the critical mounting dimensions, the “A” Series will make Marley® gear box replacements easy. Gear housing foot patterns are identical, eliminating expensive gear drive mechanical support modifications.

The input shaft diameters and keyways are the same, so existing couplings and drive shafts do not have to be replaced. All service ports are also easily accessible. Reduction ratios are within ±2% of the Marley® gear box ratios, eliminating the need to make costly fan pitch adjustments.

*Provide Amarillo Gear Company with dimensions of the input and output shafts for possible interchange modifications to the Amarillo “A” Series model selected


Ratio Selection and Gear Drive Ratings

All ratios shown in the catalog are reducing and defined as the ratio of the input speed to the output speed. Ratios shown are exact within ±2%. For your particular model and ratio, please contact the factory to confirm selection and availability.


AGMA and CTI recommend a minimum service factor of 2.0 for gear drives in cooling tower fan service when driven by electric motors or steam turbines. All ratings are service ratings and include a 2.0 service factor unless otherwise noted. Ratings listed in the catalog are for 60 cycle electric motor speeds. Ratings for speeds less than 1,750 rpm are proportional to the rated speed. Contact the factory for recommendations when the driver speed exceeds 1800 rpm or falls below 450 rpm.

Direction of Rotation

Normal rotation is both shafts clockwise as shown in the illustrations in the catalog. Occasional use with both shafts rotating counterclockwise is permissible (unless the gear drive is equipped with Amarillo Gear’s optional non-reverse backstop).

Straight Output Shaft Information

All Amarillo Single Reduction “A” Series Gear Drives drives may be furnished, upon request, with a cylindrical output shaft (no-taper). Please contact factory for pricing and availability. Rotational schemes with the shafts rotating in opposite directions are available on special order.

Other Output Shaft Selections

Marley® typically has offered up to three output shaft lengths for the Series 20, 22, 2000, and 2200. All typically feature a ½” per foot taper. They are noted as either Standard (which is generally the same as the Amarillo “A” Series standard catalog offering), Type CC (which is slightly extended in length), and Type CC2 (greatly extended in length). If you do not know which output shaft your gear box has, please complete the worksheet below and contact Amarillo Gear for proper selection or provide a certified dimensional print of your existing gear drive. A dimensional print of an Amarillo “A” Series drive with proper output shaft dimensions can be provided before ordering if requested.



Length of taper (D)_________________Keyway size (F)______________________

Small end diameter (E1)____________ Keyway parallel to centerline or taper___

Large end diameter (E2)____________ Overall Height (C)____________________








Oversized slinger on the input shaft provides adequate lubrication in either direction or at half speed operation. Continuous circulation of the oil to all bearings is assured by location of channels and baffles. Double reduction units can also be supplied with positive displacement bi-directional oil pump and oil distribution system to all bearings. This pump is driven from the intermediate shaft and provides a redundant lubrication system for extreme reliability. A permanently mounted oil sight glass is included on each gear drive.


Service Openings

The large inspection plate cover is easily removed for periodic inspections. Ports for oil fill, oil drain, and venting are tapped and located for installation of remote oil service piping when desired.


Optional Features

Special output shaft lengths, backstops (anti-windmilling), oil level switches, oil heaters & thermostats, oil temperature switches, spot-face/drill & tap for vibration transducers, “Low Speed” option and other accessory items are available on special order.


Low Speed Operation

For operation when motor speeds are less than 450 rpm, single reduction fan drives require Amarillo Gear’s exclusive “Low Speed” option, and double reduction fan drives require a mechanical oil pump for proper lubrication. The addition of these options allows operation with no minimum input speed restrictions.

Amarillo “A” Series Model Replaces
Series 27
Series 22
Series 20
Amarillo Gear
Amarillo Gear
bottom of page