Technical Question

When a pressure is set on a CPAP or APAP machine is it controlled by setting the speed of the blower or is it done by some other means? Thanks in advance for anyone who knows!

Information from a pressure sensor goes through a machine algorithm which changes the blower speed according to the rules of the algorithm.

Just curious, how else did you think pressure might be controlled?

Thanks for your reply!
I wondered if the blower ran at constant speed and a airflow restriction device at the discharge of the blower (manually set in CPAP or actuated in APAP) was used to control the output of the machine.

No, a restrictor would be hard on the blower motor--making it fail much sooner.

Thanks. I was thinking in terms of the discharge throttling of a small axial flow compressor which creates a small change in flow and a large change in pressure.

The Choker wrote:Information from a pressure sensor goes through a machine algorithm which changes the blower speed according to the rules of the algorithm.

Just curious, how else did you think pressure might be controlled?

It could be controlled by a waste gate, as is done in some turbo's and blowers, thd unneeded part of the air flow is routed or vented from the output to maintain tge needed pressure. Jim

The blower motor on a CPAP machine has a digitally controlled motor. Hence, the pressure is adjusted by varying the speed of the motor and a pressure transducer downstream from the blower measures the pressure and provides feedback to the firmware on the controller board. It's much easier to control pressure that way than to do as you suggested by having a movable vane to restrict the air flow through the system. Digitally controlled motors can switch speed very quickly and without much stress on the motor.

newpapper wrote:I wondered if the blower ran at constant speed and a airflow restriction device at the discharge of the blower (manually set in CPAP or actuated in APAP) was used to control the output of the machine.

It's the other way around: The blower speed is variable and the air restriction device (the vent port(s) of the mask) are fixed.