Considerations for Synchronous Belt Drives on HVAC Applications

Some HVAC drives will experience high starting loads if the motor has an across the line start.  The fan will be forced to ramp up to speed nearly instantaneously, and the start up loads can be as much as 150% to 200% of the normal operating loads.

Designers that are considering using synchronous belts on HVAC drives need to be aware of this potentially high start up load.

If a soft start or variable frequency drive (VFD) is used on the drive, there is no need to take any special design precautions as the load is ramped up gradually.

If an across the line start up happens infrequently, simply applying a bit more installation tension will help prevent any ratcheting or start up issues.  

If start ups occur regularly and/or frequently, it is good practice to add .2 to the service factor when designing the synchronous belt drive.  This will provide a slightly more conservative drive design that will avoid any issues at start up. Learn more about HVAC drives and synchronous belts at Gates.com.

Taper Lock Bushings

I’ve been talking to people about Taper Lock bushings for quite a while now. However, the other day, I learned something new that I thought was pretty useful. Taper Lock callouts have always seemed a bit out of left field to me, but I figured there had to be a reason behind it. Turns out there is! A Taper Lock part number is called out by four numbers followed by the shaft bore that it will attach to. The first two numbers represent the maximum bore size, and the last two represent the total length. For example, a 2012 has a maximum bore of 2.0 inches, and a length through bore of 1.25. To properly call out a 2012 bushing to fit a shaft (let’s use 1.5” for example), you call out the whole inch followed by the fraction. This means our 1.5” 2012 bushing would be called out like this: 2012 1.1/2. Metric is pretty simple, you call out the bushing followed by the shaft diameter and include MM behind it; let’s use 20mm as an example size. The Metric convention would look like this: 2012 20MM I know this will certainly speed up my answers, hopefully it will help you too!

Synchronous Belts & Exposure To Water

Light and occasional contact with water (occasional wash downs) should not seriously affect synchronous belts in general. Prolonged contact (consistent spray or submersion) can result in significantly reduced tensile strength in fiberglass belts, and potential length variation in aramid belts.

Prolonged contact with water also causes rubber compounds to swell, although less than with oil contact. Internal belt adhesion systems are also gradually broken down with the presence of water. Additives to water such as lubricants, chlorine, anti-corrosives, etc. can have a greater detrimental effect on belts than pure water.

Poly Chain GT Carbon belts use polyurethane compound and carbon fiber tensile materials that are both very resistant to water. Poly Chain GT Carbon belts can withstand prolonged contact with water without detrimental effect.

Sprockets operating in the presence of water may be vulnerable to rust and corrosion unless resistant materials or coatings are used. Sprocket corrosion can result in accelerated belt wear and tension loss. These can both shorten belt life significantly. For assistance in the design and acquisition of rust and corrosion resistant sprockets and bushings, contact Gates Made-To-Order Metal team.