Rotary Lobe and Positive Displacement Blowers
High volume, low pressure air for aeration and conveying, sized and serviced from 14 Midwest locations.
Is a rotary lobe blower right for my duty?
A rotary lobe blower is the right pick when you need a large volume of air at a steady low to medium pressure or a modest vacuum, such as aeration and pneumatic conveying. As a positive displacement machine it holds roughly constant flow as pressure changes. If your duty is only modest flow at low pressure, a regenerative blower is simpler, and high pressure is compressor work. Send us your flow and system pressure and Brabazon will size the blower before quoting a brand.
How a rotary lobe blower works
A rotary lobe blower is a positive displacement machine. Two counter rotating lobed rotors, timed by gears so they never touch, trap a fixed pocket of air at the inlet and carry it around to the discharge, where the downstream pressure pushes back into the pocket as it opens. Because a set volume moves per revolution, flow stays roughly constant as the discharge pressure changes, which is the defining behavior of positive displacement and the reason these blowers hold their delivery under a varying load. You will also hear this classic geometry called a Roots-type blower, which is simply a generic category descriptor for the straight two lobe design and not a specific maker. Modern units use two, three, or helically twisted lobes to cut pulsation and noise while keeping the same positive displacement principle.
Where rotary lobe blowers fit
Rotary lobe blowers are the workhorse wherever a process needs high air volume at a steady low to medium pressure. The most common duty is aeration in wastewater treatment, where blowers feed diffusers in the basins around the clock. They are equally at home in pneumatic conveying, moving pellets, powders, and granular material through pipe by low pressure air or vacuum, and in a wide range of process, backwash, and agitation duties. Because the flow holds steady as pressure varies, they suit applications where the back pressure shifts with the process yet the air delivery must stay consistent. When the pressure or flow demand exceeds what a compact blower can hold, the lobe blower is the natural step up.
Sizing a positive displacement blower
Size to the flow you need at the real system pressure, not the free air rating. Total the pressure losses through the ducting, diffusers or nozzles, and filters to find the actual differential pressure the blower must overcome, then select for the required flow at that differential with margin to spare. Correct for inlet temperature, altitude, and filtration, because each moves the working point and a hot or high altitude inlet delivers less mass of air. Respect the pressure limit: a positive displacement blower has no internal compression, so pushing it past its rated differential drives discharge temperature up fast and shortens life. For variable demand, plan how you will turn the blower down, whether by drive speed or staging multiple units, so it does not run wastefully at part load.
Service and failure considerations
Positive displacement blowers are durable when kept fed with clean air and serviced on time. Clean inlet filtration is the single most important habit, because ingested dust and debris scores the rotors and casing and closes the fine clearances the blower depends on. Belt driven units need correct tension and alignment, and the gear and bearing oil must be changed on schedule to protect the timing gears that keep the rotors from touching. Overheating from excessive differential pressure, a blocked filter, or a starved discharge is a frequent failure path, so monitor discharge temperature and pressure. Rising noise, vibration, or temperature are the early warnings. Our technicians rebuild and service lobe blowers in the shop and in the field.
Rotary lobe blower lines available through Brabazon
Brabazon supplies rotary lobe and positive displacement blowers from Eurus, Hardy Pro-Air, and Lone Star Turbo. We size the blower to your flow and system pressure rather than starting from a brand, then support it with parts and service.
Rotary lobe blower questions, answered first
What is a rotary lobe blower?
A rotary lobe blower is a positive displacement machine that uses two counter rotating lobed rotors to trap a fixed volume of air and push it to the discharge. It moves a large volume of air at a steady low to medium pressure or a modest vacuum, which suits aeration, pneumatic conveying, and process air. Because it displaces a set volume per revolution, its flow stays roughly constant as pressure changes, unlike a centrifugal machine.
What does Roots-type blower mean?
Roots-type blower is a generic name for the straight two lobe rotary positive displacement design, used as a category descriptor rather than a specific maker. The term describes the classic geometry where two mating lobed rotors sweep air from inlet to outlet with no internal compression. Many manufacturers build blowers of this type, and modern variants use two, three, or helically twisted lobes to run quieter and smoother. We treat it simply as a blower category.
How do I size a positive displacement blower?
Size a positive displacement blower to the required flow at the actual system pressure, not the free air rating. Total the duct, diffuser, and filter losses to find the real differential pressure the blower must overcome, then select for the flow you need at that pressure with margin. Correct for inlet temperature, altitude, and filtration, since all shift the working point. Pushing a lobe blower past its pressure limit overheats it, so size the pressure honestly and send us the numbers to confirm.
When is a rotary lobe blower the wrong choice?
A rotary lobe blower is the wrong choice when you need only modest flow at low pressure, where a compact regenerative blower is simpler and quieter, or when you need high pressure, which is compressor territory. Lobe blowers earn their place at higher flow and steady low to medium pressure such as aeration and conveying. For lighter continuous low pressure duty, see our regenerative blower page instead.
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