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Variable Speed Drives Adjustable Center

Selection Process

Factors to Consider Steps An Selecting An Adjustable Center Belt Drive

Torque and Horsepower:

Variable speed drives with constant torque loads can usually be selected by matching the variable speed pulley rating to that of the driver. Drive selection begins by matching the HP ratings, but final selection is based on torque, HP and RPM at the driven sheave. The application charts in this catalog specify driven speeds and torque ratings at the driven sheave for each pulley/sheave combination.

Retrofit

When replacing a variable speed pulley made by another manufacturer, it is important to select a Lovejoy pulley that is the same style, uses the same size belt and is as close as possible to the same diameter. The Quick Reference List on VSD-12 provides this information at a glance. If you need help with a pulley interchange, call our Customer Service Department.

Driven Speed Range (Ratio)

As a general rule, an adjustable center drive can attain a maximum driven speed ratio of 3 to 1. Most fixed center drives can attain ratios as high as 8 to 1, but part of the driven speed range is faster than the motor speed. In all cases, pulleys that use variable speed belts will provide greater speed range than those using “A” or “B” belts. Step 5:

Belt Selection

Select a suitable motor base from the catalog page for the pulley you have selected, or by reviewing the information on pages VSD-62 through VSD-64. You will need to know the NEMA motor frame size for this step. For a complete adjustable center drive package, you will need a variable speed pulley, an adjustable motor base, a companion sheave with a bushing, and a drive belt. Be sure to specify the bore sizes for the variable speed pulley and the bushing (see page SF-17). Wide variable speed belts offer several advantages over stock “A” and “B” (or 4L and 5L) belts and should be considered for all variable speed pulley drives. Variable speed belts are designed to operate over small pitch diameters, offer a broader speed range and form themselves to the pulley faces at all speeds.

Space

In some cases the amount of available space will determine the size of the pulley and whether to use an adjustable or fixed center drive. Step 4:

Shaft Sizes

Use the selection chart for the pulley/sheave combination you have chosen to find the distance between motor shaft and driven shaft (center distance) that is nearest your requirement. This will be the center distance at maximum speed position, or the point at which the motor shaft and driven shaft are closest together. Space must be provided in the machine to allow the center distance to be increased enough to attain the complete speed range. When you have found the center distance in the chart, read up or across to select the correct drive belt. Lovejoy only supplies variable speed belts. With the Econoline and Aluminoline pulley series, our selection charts will specify the pitch length of the correct V-belt to use. Lovejoy variable speed pulleys are bored to fit standard NEMA motor shafts. The bore range for each model corresponds to its horsepower rating. Consult our Customer Service Department for availability of non- standard and metric bores. Companion sheaves are bored for bushings for ease of installation, optimum performance, and availability of product.

Maintenance

Econoline and Hexadrive pulleys are virtually maintenance-free. They do not require lubrication or frequent speed change. Aluminoline and WB pulleys require lubrication and occasional cycling through the speed range for best results. There are two common selection processes; one is for designing an entire drive package, the other to select a replacement component part of an existing drive, such as the variable speed pulley. It is important to understand the complete drive selection process in order to do either. First, review the “factors to consider” and the selection examples on this page. Then follow these procedures: Typical Adjustable Center Drive
VSD

Designing a Complete Drive Package

Step 1: Step 2: Match the variable speed pulley with the motor horsepower and speed, but consider the torque and HP required at the driven shaft at all speeds. If actual torque and HP requirements are not known, rely on the fact that variable speed pulley ratings are compatible with the torque of the driver. Apply a service factor if needed. Detailed drive selection data can be found on pages associated with the pulley that has been selected. Be sure the bore capacity of the pulley is suitable for your application. Step 3: Refer to the Application chart that applies to the pulley you have chosen and select a companion sheave that suits the driven speed requirement. If more than one sheave will provide the correct speed range, select the largest one possible. This will provide the greatest amount of torque. (Lovejoy only supplies companion sheaves for wide variable speed belts.) You will also need to check the correct style bushing, bored to the driven shaft size to fit the sheave (see page SF-17). With the Econoline and Aluminoline series, the selection chart merely indicates the pitch diameter of the sheave you need to use.

VSD-8

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