ACHRNEWS

Understanding Synchronous, V-Belt Drives

May 16, 2011
The notched and wrapped belts from Emerson Industrial Automation are designed to help motors run more efficiently.

It’s time for a lesson. How much do you know about synchronous and V-belt drives? Or, how much do you want to know about them? The thought may not have crossed your mind too often but belt drives have always played an important role in HVAC equipment operation. Understanding their nuances may better serve technicians and customers.

The NEWS talked with two companies that manufacture both synchronous and V-belts, Gates Corp. and Browning Belts, a division of Emerson Industrial Automation, to find out the finer points.

According to a white paper produced by the Gates Corporation (www.gates.com) titled “Energy Savings from Synchronous Belt Drives,” manufacturing operations in the United States “spend $30 billion annually on the electricity powering motor-driven systems. Many of the 40 million electric motors in operation, which consume 70 percent of all electricity used in the plants, are not running at optimum efficiency.”

The Gates paper compares the advantages of synchronous belts over V-belts, mainly in efficiency, which equates to loss of power and ultimately, money. The paper stated, “Efficiency of any power transmission system is a measure of the power loss associated with the motor, the bearings and the drive. Loss of power is a loss of money.

“Approximately one-third of the electric motors in the industrial and commercial sectors use belt drives. If the efficiency of these systems were improved by a mere 5 percent, the plants would see tremendous energy savings.”

V-belt and synchronous drives each have a firm foothold in electric motors used in HVAC equipment - for differing reasons. Let’s explore each.

SYNCHRONOUS BELTS AND MAINTENANCE

“Synchronous belts are toothed belts in which power is transmitted through positive engagement between belt teeth and pulley or sprocket grooves rather than by the wedging friction of V-belts,” said Jay Marks, spokesperson for Gates. “Synchronous belts work on the tooth-grip principle. Round, square, or modified curvilinear belt teeth mesh with grooves on sprockets to provide positive power transmission on high-torque applications with high and low speeds.”

According to the Gates paper, synchronous belt drives are an alternative to V-belt drives and roller chain drives. The synchronous belt’s tooth profile has evolved over time from trapezoidal, to the rounded tooth of curvilinear and finally to modified curvilinear.

A synchronous belt drive maintains positive engagement between the belt tooth and sprocket groove, which results in cool operations. This positive tooth/groove engagement prevents a synchronous belt drive from slipping. In addition, the thinner cross section of a synchronous belt requires less energy to “bend” and according to Gates, “if the current airflow is satisfactory in an HVAC application, a synchronous belt drive would use less energy to do the job. If the current airflow is insufficient, a synchronous belt drive could increase airflow without increasing use of energy.”

This energy efficiency remains constant, too. Synchronous belts have an energy efficiency of approximately 98- 99 percent over the life of the belt.

On critical drives, a synchronous belt, which requires no “retensioning,” improves energy efficiency, and also eliminates downtime. More uptime equates to more production, which leads to higher profit.

Marks offered some tips for belt maintenance and replacement. “Anyone familiar with installing belt drives should recognize the need to eliminate misalignment, especially with any idler assembly or mount, by providing adequate strength at the mounting point and a sturdy framework,” he said. “Misalignment causes additional belt fatigue and wear that could result in premature drive or belt failure.

“Belts may be stored up to six years if properly maintained at temperatures less than 85°F and relative humidity less than 70 percent. For ambient storage temperatures greater than 85°, the storage limit for normal service should be reduced by one half for each 18° increase in temperature. Belts should never be stored at temperatures above 115°.”

Additional tips include:

• Don’t store belts near chemicals, oils, solvents, lubricants, or acids. Exposure to these potentially harmful chemicals can reduce belt performance and overall life.

Gates recommends replacing sprockets after every third replacement belt has reached its maximum service life, or sooner if the sprockets show significant wear. If the sprockets show significant wear, the life of the next replacement belt will be considerably reduced.

• If belt drives operate under conditions of high speeds, heavy loads, frequent starts and stops, and temperature extremes, or on critical machinery, check them for unusual noise, vibration, or visual deterioration more frequently. Depending on the critical nature of the drive, this monitoring could be necessary as frequently as every 1 to 2 weeks.

• Improperly tensioned drives will experience shorter life. Belt tension should not be too high or too low. Tension that is too low can also lead to shortened belt life or synchronous belt ratcheting, while tension that is too high adds undue stress to bearings, shafts and other related components.

• Increasing ventilation around belt drives can help reduce belt operating temperatures in applications with high ambient temperatures. This can be accomplished by adding vents to belt guards, by providing a cooler external air source, or even by adding fins to sheaves.

• Never pry or roll belts onto sheaves. This will cause invisible damage to the tensile cords and reduce belt life. Belts should be stored on a flat surface where possible. Hanging belts on hooks can cause belt crimping and lead to reduced belt life, especially with larger and heavier belts.

V-BELTS AND MAINTENANCE

Most of today’s belt drives use standard V-belts, which have a trapezoidal cross section creating a wedging action on the pulleys. V-belts depend on friction as they are part of a wedging mechanical system.

V-belt drives can run as high as 95-98 percent efficient at the time of installation. They are manufactured in a wide variety of materials, cross sections, banded multiples, reinforcement styles, and constant and variable speed configurations. Low acquisition costs, wide availability, and quiet performance make them a popular power transmission solution.

A key difference between V-belts and synchronous, in terms of maintenance is that synchronous belts do not require a run-in procedure or retensioning. It is recommended that a newly installed V-belt is retensioned 24 hours after installation. V-belt drives and synchronous belt drives demand approximately the same amount of time for installation.

“In most commercial applications the V-belt drive is the critical link and the only mechanism for mechanical transfer of power from the electric motor to the driven shaft/fan/blower,” said Don R. Sullivan, sr. product manager Belt Drives/Power Transmission Solutions for Emerson Industrial Automation. “Without high quality drive products, correct design, installation and maintenance procedures, a building owner is exposed to greater risk of unplanned downtime. By implementing a V-belt drive preventive maintenance program with sound fundamentals, (such as using premium V-belts, checking sheave wear, tensioning belts, and verifying alignment), building owners can ensure reliable drive performance and avoid inconvenient and costly repairs.”

Sullivan said that in the past few years there has been a trend by users to specify notched/cogged style V-belts vs. traditional wrapped style V-belts. He noted, “The U.S. Department of Energy publishes that notched/cogged V-belts have slots that run perpendicular to the belt’s length. The slots reduce the bending resistance of the belt. Independent tests results show notched V-belts are 2-3 percent more efficient than standard wrapped style V-belts.

“To put this in perspective, switching from a wrapped V-belt to notched V-belt on a single continuously operating 10hp drive operating at 75 percent load, and an electricity rate of 012.8 kWh results in annual savings of $255.26 (assuming a 3 percent efficiency gain). A facility with 20 rooftop units could save about $5,105.20 per year and payback would be just a few days for the belt upgrade.”

WHAT THE FUTURE HOLDS

Sullivan said that given the increased desire for efficiency by building owners, V-belt drive optimization and retrofits, as well as sustainability projects, should gain momentum. “Many older units are ideal candidates for an efficiency evaluation as old worn sheaves (sometimes called pulleys) can easily contribute to efficiency losses due to less sidewall contact with the V-belt and resulting slippage,” he said.

“In the past 20 years there has been a trend by the industry to downsize the footprint of commercial HVAC equipment. This downsizing has resulted in shorter center distances of the V-belt drive (center distance is distance between motor and driven fan/blower shaft). A shorter center distance results in the actual V-belt length being shorter, and thus the belt seeing more operating cycles and even having higher operating temperatures.”

If you want more information on belt drives, Sullivan suggests participation in workshops. “Browning, a division of Power Transmission Solutions for Emerson Industrial Automation, offers a three-hour NATE-recognized educational seminar that not only covers important V-belt drive troubleshooting and maintenance procedures but also provides continuing education credit,” he said. “In addition to seminars, Browning offers a full suite of information on our website and training videos are posted on YouTube for a variety of belt drive topics.”

For more information, visit www.gatesprograms.com/ptsavings or www.emerson.com.

Publication date: 05/16/2011