[Equipment] Cpap not blowing

[WillyBilly]

My cpap machine (DeVilbiss) blows pressure when the mask is off, but when I put the mask on, it stops blowing. What is wrong with my machine?

[Sleeprider]

Your machine is designed to supply enough flow to provide therapy pressure. The only airflow you should feel is from the exhaust vent on the mask or a leak.

[chill]

It does not blow pressure when the mask it off.  It blows volume trying to create pressure (which is not possible as the mask is off).  Once you put it on, the volume reduces to maintain the configured pressure.  Unless your machine is shutting off when you put the mask on, it is working correctly.  If it shutting off, then there is a problem with it.  Get it serviced or replaced.

[trish6hundred]

Hi WillyBilly,
WELCOME! to the forum.!
I hope you figure out what's wrong with your machine, hang in there for more responses to your post.
Good luck to you.

[kwhenrykerr]

I often check the vents to see if my machine is working. It has always been working fine.

[Sleepster]

My cpap machine (DeVilbiss) blows pressure when the mask is off, but when I put the mask on, it stops blowing. What is wrong with my machine?

There's nothing wrong. When you have the mask on your face it creates an obstruction and this allows the pressure to build in the hose. When you take the mask off you remove the obstruction and the pressure in the hose drops. This causes the machine to spin the fan faster in a futile attempt to raise the pressure. If you leave the mask off long enough the machine will likely give up and shut down.

[holden4th]

An easy test is to lift the mask slightly from your face. If the machine is blowing you will both hear and feel it. If the machine is not blowing you will feel as if you are suffocating.

[eseedhouse]

Your airway and the hose from the machine (ignoring for the moment your face mask) are a closed system. As such the machine will only blow until that closed line fills up until the pressure is equal to or greater than the pressure the fan generates. Now if it were entirely closed you would soon top breathing because of too much carbon dioxide in the airway. And that would kill you.

So, to prevent that, your mask has an intentional built in leak so the carbon dioxide you breath out can be blown away. With most masks you can feel this by putting your hand in front of it in the right spot.

Think of blowing up a balloon. When the balloon is deflated your breath goes into the balloon, but when the balloon is as fully inflated as it can be then you can't blow any more air in no matter how hard you try. Or else, it will pop, of course.

Or take a short 1/2" pipe, cover the other hand with your hand and blow. No matter how hard you blow once the pipe is pressurized by your breath no more air will flow into it.

The idea of a CPAP machine is to pressurize your airway so the difference between the inside pressure and the outside pressure will cause it to "inflate" slightly, enough so the airway stays open. Once the pressure is high enough for this no more air will flow into your airway from the CPAP machine even though it will continue to blow so that your airway remains pressurized. What it will be then doing is preventing the pressure in your airway from dropping back down so that your airway stays open.