17 cmH2O is how many MPH in air flow ?

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Hi everybody, its been a while.

After 10 months I no longer Ramp; however, I still sleep with a Oximeter. I still upload my Resmed SD and Oximeter data every morning and although I haven't address large mask leaks as yet I plan on doing just that in another month.

Thanks to CPAP I am sleeping better and some mornings I hate to get out of bed because it feels so good to just rest. So I have to take my Hat Off to CPAP. The First couple of weeks were something else, but it was well worth the effort. I want to thank everyone for their assistance when I was having a difficult time in getting started.

I now have an Anemometer, an instrument or gauge that measures wind speed, and I would like to keep check of my CPAP Machine's air flow.

Does anyone know how to break down 17cmH2O into a MPH reading?

At present my Anemometer is reading 24 mph at the end of my air hose. My machine is suppose to be set at 17 cmH2O.

My Anemometer measures wind force in the Following: MPH, m/s, Km/h, ft/min, Knots.

If you know how to figure cmH2O to MPH, please let me know.

Thanks Everybody, K

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Hi Jimster
I think your anemometer reading is about the best you can do...though without the back-pressure of the mask on your face I doubt you were getting 17cmH2O.

Mathematically I don't see how you can convert a pressure into a velocity without looking at all the variables.

You could have the hose stopped off with 0mpg and yet still have 17cmH2O.

Or, with a large enough blower you could have 100mph and still 17cmH2O.

See my point? And then the question becomes...why is that important?
J

Hold your xpap out the car window and read your speedometer. Pressure doesn't mean speed, think firehose and nozzles. Jim

The following is my opinion, and might or might not be fact:

The measurement of cm of water is a static measurement ... how much water in CM can be raised by a given pressure.

I believe the speed of air is not directly convertible to that measurement.

That same 17cm through a straw would, I think, move faster.

But I'm not positive ... just seems right to me.

Wind speed may vary, depending on the tube diameter.
You need to directly measure the pressure in centimeters of water pressure.
Lower the end of your hose into any container of clean water, keeping the hose vertical;
and measure in cm the distance between the mouth of the hose
and the surface of the water exactly when the air bubbles stop.

I do not think you can compare that. Maybe with Bernoullis Ekvation.

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Well, of course, Thanks Everybody for all the replies.

The reason the I want to keep check on my machine is just to make sure that it is operating at the correct pressure level.

Recently the Resmed S-9 that I was using had a few open areas on the Constant Pressure Graph. I informed my DME of this and they replaced that 6 month old machine with a new one. Now, between the time that they replaced my existing machine with the new machine I used my existing machine without a problem for 4 days.

I know that replacing my existing machine with a new one has nothing to do with checking the air flow pressure, but my DME has someway to set the correct setting on the machines before they leave their shop.

I picked up the new machine as I was returning home from out of town, and ended up with both machines for a week end. During that time I checked the air flow on both machines with my gauge and they both read 24 mph. I also closed the air hose off on both machines with my hand while they were running for 3 seconds and then I took another reading 5 seconds later on both machines and both machines read the same again.

The DME's have some way to set our CPAP Machines to our prescribed level, and when I find out how they accomplish this task I will let you know, although I understand you may already know.

Thanks, K

no matter how you measure it, your cpap still doesn't have enough pressure to blow up a balloon. stick a new balloon on the end and try it. it only fills the original form of the balloon. it doesn't inflate it at all. the psi of the air coming from the machine is somewhere around .2 or .3 psi depending on your setting.

Guest wrote:...

Well, of course, Thanks Everybody for all the replies.

The reason the I want to keep check on my machine is just to make sure that it is operating at the correct pressure level.

Recently the Resmed S-9 that I was using had a few open areas on the Constant Pressure Graph. I informed my DME of this and they replaced that 6 month old machine with a new one. Now, between the time that they replaced my existing machine with the new machine I used my existing machine without a problem for 4 days.

I know that replacing my existing machine with a new one has nothing to do with checking the air flow pressure, but my DME has someway to set the correct setting on the machines before they leave their shop.

I picked up the new machine as I was returning home from out of town, and ended up with both machines for a week end. During that time I checked the air flow on both machines with my gauge and they both read 24 mph. I also closed the air hose off on both machines with my hand while they were running for 3 seconds and then I took another reading 5 seconds later on both machines and both machines read the same again.

The DME's have some way to set our CPAP Machines to our prescribed level, and when I find out how they accomplish this task I will let you know, although I understand you may already know.

Thanks, K

The instrument you probably need is called a manometer which measures pressure in CM of H2O. Search the forum and you'll find threads on how to build one.

Pressure is the key measurement though some machines such as an avaps are volume sensitive as well.

With a manometer, you can check to be sure your machine is putting out the pressure it's set at.
J

Actually, Jim, the machines are programmed via their buttons or the SD card ... they are well-calibrated from the factory. So you tell it, for instance, to use 17cm and it does, no separate tools necessary.

Now you can indeed use a manometer to check its accuracy, but these days there's very little need for that other than to double-check.

For an online calculator go to:


http://www.engineeringtoolbox.com/dynam ... _1037.html

But for a quick answer - 30 mph = 17 cm H2O approximately.

Cheers

When I had my old Sullivan cpap I made my own manometer by taking a one inch clear piece of plastic tubing (about 4 feet in length) and mounting it to a board in a "U" shape. By filling the tube half full with water and applying the cpap tube to the inlet, I would measure the amount that the cpap moved the water in the tube. 10cm of movement equaled a setting of 10.

If your to lazy to build one, you can buy one here: https://www.cpap.com/productpage/guage- ... ssure.html

When my wife found that I tore a fence board off the fence to use as a "tube holder", I went down to the local fencing company to buy a new one, at about 35mph...

It would be interesting to have one, but how often are you going to use it?

JDS74 wrote:For an online calculator go to:


http://www.engineeringtoolbox.com/dynam ... _1037.html

But for a quick answer - 30 mph = 17 cm H2O approximately.

Cheers

It's certainly true that the moving air hitting a surface creates a pressure - architects and all sorts of engineers as well as sailors and pilots learn to do these calculations - but it does not apply in this situation. Here the xPAP is not sensing any pressure so it increases the flow until the pump maxes out. In normal operation the velocity is related to flow volume, not the pressure.

DNFTT's

Cheers