May 22, 2019
Types of Power Transmission
There are various types of power transmission devices commonly used in industry today. Among them for example, chains, gears, v-belts and synchronous belts are widely used. The focus of this exercise will be a general introduction to rubber power transmission belts and more specifically, those v-belts and synchronous belts used in the Heating, Ventilation, Air Conditioning and Refrigeration (HVAC-R) industry.
Power Transmission Belting
The primary function of a belt is to simply transfer rotation from the powered driver pulley to one or more driven pulleys. The belt must be designed and capable of transferring this torque efficiently and reliably. Generally, the most economical component in the system, belts can also act as a “safety fuse” by slipping or breaking under a peak or shock load situation, such as when a drive becomes jammed by debris, which can protect the more expensive components of the system.
Advantages of Power Transmission Belts
- Lowest cost means of transmitting power
- Ability to accommodate a wide range of speeds and center distance between driver and driven shaft
- Quiet and clean operation
- Require no lubrication like chains, gears and gearboxes
- Able to absorb shock loads and pulsations
- Can be used for special applications such as clutching and variable speed
Two Major Types of Power Transmission Belts
There are two major types of Power Transmission Belts. These are V-Belt and Synchronous Belt (also commonly referred to as timing belt).
The terms “sheave” for v-belt drives and “sprocket” for synchronous drives and “pulley” (for all drives) are commonly used when referring to the “wheels” used connect the belt between the driver and driven units of different types of belt drives. The International Standards Organization (ISO) uses the term pulleys for all drives whether they are v-belt or synchronous.
The V-Belt is a friction device and works on the principle of the wedge. It relies on tension to create friction on the sidewall of the sheave to transmit power. It is non-synchronous and allows slippage. Slippage can be desirable and intended in drive design. For example, in a fan where the belt must slip rather than break the belt or bend a shaft if the blade contacts something or is blocked. V-Belts are the most basic belt utilized for power transmission and are generally speaking, also the most economical.
- Less expensive than most other forms of power transmission
- Start, stop and run smoothly
- Operate noiselessly and without lubrication
- Absorb objectionable and harmful vibrations
- Clean and require minimum maintenance
- Rugged and long lasting
- Accommodate a wide selection of speed ranges
- Cover an extremely wide horsepower range
- Easy to install and simple to replace
- Relatively unaffected by moisture, abrasive dusts, or extreme variations in temperature
Two types of V-Belt Construction are Commonly used in Industry:
- Wrapped V-belt – has a protective fabric cover and will allow some slippage in peak torque situations. Slippage can be advantageous in some drives to avoid damage to belt and other drive components
- Raw Edge V-belt – has fabric on the top and bottom but no fabric on the “raw edge” sides. This construction resists slippage with more grip on the sheave sidewalls due to the exposed rubber sidewall that has no fabric as a wrapped v-belt does. It is advantageous in drives where minimum slippage, maximum efficiency and power transmission is required. It will still allow slippage but is more resistant to slippage than a wrapped v-belt.
V-Belt Types and Sizes
V-Belts come in a wide variety of sizes and lengths. They are identified by their various cross sections and length. The common types used in the HVAC-R industry are listed in the table below.
Synchronous or timing belt is a positive engagement device and relies on the accurate meshing of the belt teeth with the sprocket grooves. It does not allow slippage. There are drives where slippage can cause damage and must be prevented. For example, the valve train of some internal combustion engines. If the drive does not maintain synchronous operation the piston can contact and damage the valves. Converting an HVAC V-belt drive to synchronous belt is a way to gain a significant efficiency increase and resulting energy savings.
Use a Synchronous Belt Drive when:
- High mechanical drive efficiency and energy savings are a priority
- Synchronous transmission and precision positioning between shafts is required
- Low maintenance is a priority
- High torque, low RPM requirements
- Compact drive layout is necessary
- Low noise requirements (compared to chain and gears)
- Environmental or contamination concerns (no lubrication required such as with chain)
Detachable Tab Link Type V-Belt
Detachable Tab Link V-Belt is an ideal alternative to conventional rubber v-belts in many applications. Made endless by hand using no tools, an open length of belt can be assembled from tabs (like links in a chain) and wrapped around pulleys in hard-to-fit applications yielding fast belt replacement.
- For use in applications where it’s difficult to install an endless conventional v-belt, avoiding costly labor-intensive machine dis-assembly.
- Ideal for use on mobile service vehicles where carrying a large inventory of v-belts is not practical. A long roll of detachable tab link type v-belt can be carried on the vehicle and any length of belt can be made versus carrying a large inventory of conventional v-belt sizes. Eliminates the possibility of being “out”” of a needed size.
- Can be used either as singles or on multiple v-belt drives. Widely used in HVAC, poultry, agriculture and general industry.
- Increased calls per day for mobile service vehicles (reduced labor cost and travel spent searching for the right v-belt)
- Less vibration and noise than conventional v-belts