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Industry, Wastewater

Ask Atlas Copco: Are High-Speed Turbo Blowers Reliable? Part I

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Ask Atlas Copco is a segment that discusses commonly asked questions about various compressor, vacuum, and blower technologies, processes and best practices. Today’s answer comes from Paul Petersen, regional manager for blowers and low-pressure compressors.

High-speed turbo blowers (HSTB) have been a hot topic in the wastewater industry for the past ten years. While some plants operate well with them, others do not, leading to the question, Are turbo blowers reliable? The answer lies in the blower design, environmental conditions of the plant and operating conditions.

Today, we’ll examine the impact of blower design, specifically bearing types, motor cooling methods and blow-off valve types.

Bearing Types

There are two main types of non-contact bearings used in blowers: air foil and magnetic. Air foil bearings are relatively simple in design and low in capital cost. There are no bearing controllers and complex sensors to worry about, but if air foil bearings become overloaded, surge can cause a cascade of failures within the blower.

In recent years, HSTBs with magnetic bearings have become increasingly popular. They have a slightly more complex design than air foil bearings, because magnetic bearings allow the machine to tightly control impeller clearances and provide a dynamic response to choke and surge, protecting the blower and motor in nearly all situations. 

Motor Cooling

The method of motor cooling also impacts the reliability of turbo blowers. Air-cooled motors are more susceptible to ingress of foreign particles such as particulates corrosive gasses and rust that can damage the motor. If not maintained properly, air-cooled motor parts, like windings and bearings, can overheat.

Water-cooled motors pass cooling water through the jacket around the motor to reduce heat. In the best systems, several sensors monitor conditions and carefully maintain temperatures, ensuring high efficiency and reliability.

Blow-off (Safety) Valve 

The final element of blower design that can impact overall reliability is the blow-off or safety valve. Fast-acting blow-off valves (also referred to as FABOVs) are typically used in conjunction with air foil bearings in high speed turbo blower packages. FABOVs do have limits — if the shaft comes in contact with an air foil bearing, components can become fused together, causing catastrophic failure. To prevent any issues, these blow-off valves must be, well, fast. They must be fully open in a matter of milliseconds to avoid failure.

Modulating blow-off valves are used on some magnetic bearing HSTB designs. When the blower controller senses a surge condition, a signals are sent to the drive to speed up and to the modulated blow-off valve to slightly open. Because the magnetic bearing controller monitors and controls the shaft position, a FABOV isn’t necessary. 

In part two, we will examine how environmental conditions and operating conditions can influence turbo blower reliability, and determine a few ways you can ensure your blowers continue to support your application. Check back next time to get the full story, and don’t forget to subscribe to our weekly newsletter.

 

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