The “Roots,” lobe-style blower is a type of positive displacement (PD) blower, the latter of which was invented in the late 1850s by the Roots brothers. Positive displacement blowers operate with flow and pressure as independent variables; this means that if pressure increases and speed remains constant, the flow rate is largely unaffected. Keeping this in mind, PD blowers are ideal for applications that require variable flow and pressure.
Despite the Roots blower having been around for over 150 years, the primary advancement in lobe technology over this time frame hasn’t been focused on improving efficiency, but rather on noise reduction. Bi-lobe blowers produce very high amplitude waves at a low frequency; to reduce the amplitude and increase the frequency of the waves, a third lobe was added. While this innovation decreased efficiency slightly, it reduced noise levels to below 85 dBA as mandated by OSHA.
How Does a Roots Blower Work?
Roots blowers are typically oil-free, air-cooled technologies comprised of two rotors that spin in opposite directions. Once the compression chamber comes into contact with the outlet port, compressed air flows back into the housing from the pressure side. Further compression takes place as the volume of the compression chamber further decreases with continued rotation. This means that the compression occurs against full counter-pressure, which results in low efficiency and a high noise level.
The low-efficiency of these blowers limits them to applications requiring very low pressure and single-stage compression. These are also frequently used as vacuum pumps and for pneumatic conveyance.