Minimal manometer

TerryB · Post by **TerryB** » Wed Apr 12, 2006 8:34 am

In order to be able to verify the output of my CPAP I decided to build a manometer with minimum parts.

I took an 8 inch length of plastic tube such as for aquarium pumps or the like 1/8 " ID., I taped it to an engineers scale, which is a dual unit ruler 6 inches long. I left a tail hanging below the 0 end of the scale.

I placed the assembly in the water in the humidifier and turned on the machine with the scale 0 at the water line. When I used my fingers wrapped around the ruler/tube/outlet port to reduce the air leakage, the water moved up the tubing until it reached my setting of 12 CM. Further reduction of the leakage did not raise the water any higher.

The only way to be simpler would be to mark the CMs on the naked tube alone.

TerryB

Guest · Post by **Guest** » Wed Apr 12, 2006 2:11 pm

Where do you start measuring from? The top of the water line in the humidifier?

TerryB · Post by **TerryB** » Wed Apr 12, 2006 2:48 pm

That's right, move the 0 of the scale to the surface of the water and the height of the water column within the tube above there is the pressure in CM of water column.

TerryB

neversleeps · Post by **neversleeps** » Wed Apr 12, 2006 4:43 pm

Here's a picture from a previous post by derek along those same lines:

derek wrote:Take a length of clear plastic tubing, about two feet in length.
Fashion a cork or stopper that will fit snuggly into the outlet from the humidifier, and drill a hole through the cork that provides a snug fit for the tubing. Push the tube through the cork with enough length to allow the end to be under the water in the humidifier, Use rubber bands to attach the other end of the tube to a ruler with a centimeter scale, as shown below

That's all there is to it!

Fill the humidifier, and insert the cork into the outlet. When you turn the macihne on, the pressure will force the water up the tube. To make a measurement, simply place the 0 cm scale on the ruler at the level of the water in the humidifier, and read the height of the column.

In the photo I added some food coloring to make the water column stand out, but it's not really necessary. You can see that the column is showing 10 cm (100 mm).

Notes: 1) You may have to bend the tube near the cork to allow the water to flow (siphon) over the loop and fill the tube, especially if you are working at a low pressure.
2) Be careful to keep the open end of the tube sufficiently high above the machine, otherwise the CPAP pressure will blow the water out and ruin your carpet.

TerryB · Post by **TerryB** » Wed Apr 12, 2006 5:06 pm

Yup, I found this post during my searches, but decided to do away with the food color, cork and cut to the bone. No need for the siphon action to get water outside the tank, the pressure will push the water straight up to the same level. Just a minimal approach.

TerryB

tomjax · Post by **tomjax** » Wed Apr 12, 2006 8:37 pm

Nice trick. rube goldberg.

Being lazier than you, I simply hold the bottom of the hose to a ruler and dip it into a pan of water- about 6 inches and turn the machine on.
I then simply raise it slowly until the bubbles start escaping and look at the ruler.
This is the cm/inches of water.
Works for moi.

1 in= 2.54 cm