BELT DRIVE MONTHLY | October, 2009
CAN YOU EXPLAIN WHY WORN SHEAVES
(V-BELT PULLEYS) CONTRIBUTE TO ENERGY
EFFICIENCY LOSS?
WORN SHEAVES
In a v-belt drive the wedging of the belt
in a sheave groove creates friction when
tensioned. This friction allows horsepower to be
transmitted from the driver shaft (motor side)
sheave to the driven side sheave when the drive
is operated.
1/32” WEAR
FIGURE 1
The groove of any given sheave is machined at a
specific angle based on diameter and type of belt
to be used. This is because a belt cross section
actually changes as it wraps a radius. The size of
the sheave and ultimately the radius determine
what groove angle is required. For example,
a sheave roughly 8” in diameter machined for
“B” style belts will have a 38° groove angle. In
contrast a 4” sheave machined for “B” style
belts will have a 34° groove angle. This angle is
designed to place the belt in an optimal position
so that when the belt is tensioned the sidewalls
expand and make contact with the sheave. This
angle also ensures equal stress is placed on
the belt tension cord members. A v-belt drive
with sheaves in good condition using cogged or
“notched” style v-belts with appropriate tension
can be up to 98% efficient.
Over time friction between the sheave and
the belt erodes sheave material no differently
than water would erode a rock in a stream.
When sheaves become worn the sides of the
sheave angle start to cup and have a concave
appearance and the belt has less area of contact
with the sheave and slips (see figure 1). Energy
efficiency is then quickly eroded. A 6% loss in
efficiency due to belt slippage for a single 20HP
drive operating 7 days a week 24/7 at 12.8 cents
a kilowatt hour translates to an added $511.92 in
added electricity charges.
Heavily worn sheaves are quite visible to the
eye and even to the touch as you run a finger
in the groove wall. However, many sheaves
can appear acceptable, but actually are worn.
When a straight edge or groove gauge is placed
in them it becomes more apparent. In order to
maintain efficiency sheaves should be replaced
once 1/32” or more of wear is visible. (Typically
after every 5-7 annual belt changes).
Worn Sheave
CAN YOU EXPLAIN WHY WORN SHEAVES (V-BELT
PULLEYS) CONTRIBUTE TO ENERGY EFFICIENCY LOSS?
CAPTURING ENERGY SAVINGS
Many service technicians do not realize the significant impacts a few
points of efficiency in a v-belt drive can have on their customer. Replacing
worn sheaves can have very rapid payback. In the example on page one,
the added annual electricity use of $511.92 on just one unit could easily
have paid for replacement sheaves in just a couple of months. Building
owners, facility managers, and maintenance technicians need to be aware
of the impacts of worn sheaves and the importance of maintaining drive
efficiency. All preventive maintenance programs that utilize v-belt drives
should incorporate a sheave inspection and replacement program to ensure
electricity costs are minimized.
ACCEPTABLE SHEAVE
TOOLS TO HELP
We offer many tools to help customers maintain efficiency in their v-belt driven equipment. Some of the most
popular items are listed below.
• Belt Drive & Bearing Reference Guide (Form #8932)
- Offers basic product information, installation
information, preventive maintenance, and
troubleshooting tips in a pocket size format.
• Save The Green Energy Responsibility Flyer
(Forms #MCF08073 and #MCF08024) - Offers energy
responsibility in three easy steps.
• Belt Efficiency Calculator
• Belt Drive Maintenance and Installation Video
Available at www.RegalPTS.com or on CD by
request.
• Sheave Wear Technical Bulletin (#1007)
Offers explanation of groove gauge usage
and sheave wear dynamics. Available from
Application Engineering.
Available at www.RegalPTS.com. Allows user to
quickly calculate the savings benefit of converting
from wrapped style v-belts to cogged or “notched”
style v- belts.
Regal® Power Transmission Solutions
7120 New Buffington Road
Florence, KY 41042
Customer Service: 800-626-2120
Fax: 800-262-3292
Technical Service: 800-626-2093
Future article ideas or questions can be
Submitted to [email protected]
www.RegalPTS.com
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