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Text version of the page
N For this catalog, Lovejoy terminology will refer to any variable pitch pulley as a “pulley” and to any non-variable pulley as a sheave, driven sheave, or companion sheave. The RPM at the driven shaft is found by the following simple equation: N
D = N
d x d/DWhere N
D is the RPM at the driven shaft N
d is the RPM of the driving shaft d is the pitch diameter of the driver D is the pitch diameter of the drivenSince N
d is always a fixed RPM, it can then be seen that by changing the pitch diameter of either d or D, the driven RPM will change.
D , will decrease proportionately.The photos at right (Adjustable Center V-Flat Drive Maximum Speed Position and Adjustable Center V-Flat Drive Min. Speed Position) show a V-Flat drive, so called because the driven sheave is flat, not grooved. The pulley is called a one- side moveable type because it has only one spring and one moveable flange.Note that in the Adjustable Center V-Flat Maximum Speed Position figure, the drive is at the maximum speed position, with the variable speed pulley flanges closed together and the belt at the maximum pitch diameter. As the motor base is adjusted to increase the center distance between the motor and the driven shaft, the moveable flange on the variable speed pulley opens to allow the belt to run at a smaller pitch diameter (Adjustable Center V-Flat Drive Minimum Speed Position).
VSD You must refer to page VSD-2 (Page 342) for Important Safety Instructions and Precautions for the selection and use of these products. Failure to follow the instructions and precautions can result in severe injury or death.
Variable Speed Drives - 7199 Variable Speed Drives
Overview
Why Vary Speed?
Variable speed drives are needed because many applications are not run at the same speed all of the time, due to the surrounding conditions. Revolutions Per Minute (RPM) of the driven shaft need to be increased or decreased when there are changes in load conditions, application requirements, or other circumstances. Variable speed belt drives achieve the versatility needed to maximize application efficiency and productivity while remaining an inexpensive solution. In the most typical installation, a belt connects a variable speed pulley to a driven sheave. The pulley is mounted on a motor shaft and the motor is at constant speed. Thus, the speed at the driven shaft is a ratio of the pitch diameters of the pulley and sheave. Note:D = N
d x d/DWhere N
D is the RPM at the driven shaft N
d is the RPM of the driving shaft d is the pitch diameter of the driver D is the pitch diameter of the drivenSince N
d is always a fixed RPM, it can then be seen that by changing the pitch diameter of either d or D, the driven RPM will change.
Common Mounting Methods
1) Adjustable Center Drives
This type of belt drive consists of one pulley and one sheave. The pulley is spring-loaded and is usually mounted on the driver shaft. The driver is most often an electric motor which is mounted on an adjustable motor base that can be moved toward or away from the driven sheave. The springs in the pulley take up any slack in the belt when an adjustment is made.When the base is adjusted, moving the pulley toward the sheave, the RPM at the sheave increases. Likewise, when the base is adjusted away from the sheave, the RPM at the sheave decreases. In the photo at right (Adjustable Center V-V Drive), the drive is at its maximum speed position. This is called a V-V drive because the driven sheave is grooved. The pulley is called two-side moveable because it has two springs (one against each flange) and two moveable flanges.Notice that the belt in the pulley is at the maximum pitch diameter, or “d” as mentioned in the previous equation. As the base is adjusted away from the sheave, “d” will decrease and the driven speed, N Adjustable Center V-V Drive Adjustable Center V-Flat Drive Maximum Speed Position Adjustable Center V-Flat Drive Minimum Speed PositionD , will decrease proportionately.The photos at right (Adjustable Center V-Flat Drive Maximum Speed Position and Adjustable Center V-Flat Drive Min. Speed Position) show a V-Flat drive, so called because the driven sheave is flat, not grooved. The pulley is called a one- side moveable type because it has only one spring and one moveable flange.Note that in the Adjustable Center V-Flat Maximum Speed Position figure, the drive is at the maximum speed position, with the variable speed pulley flanges closed together and the belt at the maximum pitch diameter. As the motor base is adjusted to increase the center distance between the motor and the driven shaft, the moveable flange on the variable speed pulley opens to allow the belt to run at a smaller pitch diameter (Adjustable Center V-Flat Drive Minimum Speed Position).
VSD You must refer to page VSD-2 (Page 342) for Important Safety Instructions and Precautions for the selection and use of these products. Failure to follow the instructions and precautions can result in severe injury or death.