A hose from my oxygen concentrator connects to the smaller barbed tube on the adapter. One end of the adapter is connected to hose coming from the CPAP. The other end is connected to the air inlet on the face mask. This adapter is intended to mix O2 with the pressurized air from the CPAP.
It seems to me that the amount of O2 “bled” into the CPAP hose would depend on the pressure of the O2 being somewhat greater than the air pressure provided by the CPAP. This means to me that if my concentrator is putting out 4 liters per minute of O2, something less than that is actually reaching the CPAP mask. If the CPAP pressure is too great, does little or no O2 actually get to the mask?
Until it’s nearly empty the O2 cylinder will have a much higher pressure than the machine.
This is from a UK site but it is probably the same wherever you are:
The oxygen is stored in the cylinders at 2000 psi with a pressure regulator that allows 50 psi to the patient. The valves provided have a medium setting, which delivers 2 l/min, and a high setting, which provides 4 l/min.
I think this is where your confusion lies. The concentrator will raise the pressure (within limits) for the O2 to reach your mask. Rest assured, the flow rate shown on the O2 concentrator rotameter is what is reaching your mask.
@Mortimus - Oxygen concentrators typically use scroll compressors - which are positive displacement compressors.
A good way to understand their operation is to think about a syringe. The compressor is like a syringe, designed to deliver say 5 syringe fulls per minute. If you obstruct the outlet of the syringe, the piston will be pushed harder , but you will still get the same flow.
By that line of thinking, if I were to place my finger over the end of the O2 hose and hold it for a little bit, the pressure should build up as the compressor attempts to overcome the resistance caused by my finger. Removing said finger should result in a ‘whoosh’ of O2 as the built up pressure is released. But that doesn’t happen. Also, the syringe may not be a good metaphor for what’s going on. Gases like air and oxygen are highly compressible whereas liquids are not so much.
See Pneumatic Diagram on Page 15 of the owner manual of a typical oxygen concentrator
See the relief valve on the compressor ? If you close the outlet, the relief valve will open when a set pressure is reached.
(Within Limits) in my original post was about the relief valve without getting too technical.
I have taught many junior engineers about reciprocating compressors and positive displacement compressors very well with the syringe analogy. I am sorry you don’t find the analogy useful.
Of course - that goes without saying. Compressors are used for gases.
Pumps are used for liquids. What are you trying to say here ?
Most Gasoline car engines are like the syringe, btw.