White paper: ‘How a highly reliable blower is developed for driving mechanical ventilators’

Executive summary

Mechanical ventilator systems driven by blowers are in rapid development. Market demand is strongly growing mainly due to large benefits of these small size ventilators. As a pressurized gas source is omitted, blower driven ventilators can be easily transported within hospitals and for emergency use. This leads to easy logistics as well as avoidance of multiple patient dis- and re-connections which is the case when using conventional ventilators. Ventilators equipped with well-designed blowers provide high performance, low noise, low energy consumption and a high reliability. Such a high performing blower can even facilitate operation without internal flow valves, allowing manufacturers to develop ventilators with less complexity and costs.
Reliability and long lifetime are of vital essence for mechanical ventilators.

This paper explains how a blower with a long lifetime is developed by using reliability testing. DEMCON macawi respiratory systems developed such a blower with small and lightweight impeller which is able to run over 85.000 RPM. The blower has a target lifetime well beyond 40.000 operating hours, resulting in 10 to 15 years technical operation and comparable to the typical commercial lifetime within hospitals. After design and prototyping of the impeller and motor multiple, so called, HAST and Lifetime tests have been executed to verify the actual lifetime. HAST testing was also used to “enforce” failures using extreme use scenario’s so to reveal design issues in an early development stage. The main engineering topics to influence blower lifetime are; Impeller design and material, Impeller-motor shaft interface, Blower pressure (fluctuation), Blower temperature, Imbalance of the impeller and motor speed and, of course, bearing system choice. The impact on reliability was measured during HAST and Lifetime testing. In order to achieve an L10 lifetime 40.000 hours operating time under standard conditions, the HAST test target was set to a minimum of 11.000 hours without failure under extreme use conditions. This was successfully achieved. Although these targets were achieved, it was decided to further enhance the design of the blower, by re-enforcing the bearing system and to increase the size of the motor. These enhancements both reduce the operating motor temperature and improve the blower lifetime. In all commercial models this update is incorporated. Lifetime testing under standard conditions revealed no issues. Samples which were dismantled and cut after successfully operating for 10.000 hours, did not show any signs of wear. Test results confirm our target technical lifetime of more than 40.000 hours.

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