Make your own Manometer (for testing screen pressure)

[Doug Miles]

What's a Manometer you ask? A manometer is a device which is used for measuring pressure. In a simple form, a manometer is a column or tube filled with a liquid. Pressure is applied at one end (or in some cases, both ends) and the distance the liquid moves within the tube represents the amount of pressure. You will often hear pressure measurements quoted in inches. This means that the liquid being used will move X number of inches when the pressure is applied. There are many different types of manometers, and they are used for measuring many different types of pressure. For instance, when measuring blood pressure, a glass tube is filled with mercury. The mercury rises within the tube, and a pressure reading is made. Be careful when comparing pressure readings between devices and equipment. The liquid being used makes a HUGE difference in the number of inches of pressure. Some liquids are more dense than others, and therefore require more pressure to move the same distance.

So, first you need to go buy a jar of mercury. No, sorry, just kidding. Instead of mercury we will be using water. We will use water mainly because that is what most inflatable blowers quote their static pressure against (inches of water).

Here is a picture of my finished product. Below I give details how I made it:



Continued on next post.

[Doug Miles]

Here is what you will need:

10 feet of vinyl tubing
A board (to mount tubing on)
Zip ties
Drill

I bought 10 feet of 1/2" (inside diameter) tubing at Home Depot for about $5.00. You can use any size/diameter tubing you want, it won't effect your measurements. I wasn't sure about this, but I did a test to confirm this (see below). The board I used is actually a $5.00 shelf (also from Home Depot). I used white because I was concerned that I might not be able to see the water level in the tube, and I thought I might need to add food coloring to the water. It turns out I didn't need to add food coloring, but I recommend a white board anyway. Also, you can use anything you want to attach the tube to the board, I just happened to have zip ties around, so I used them. I think string will work just as well.

Here is a picture giving an idea of the size of tubing I used:



Nothing here needs to be exact. We're not sending a rocket to the moon, so I will skim over basically what I did.

First, I drilled some holes in the board:



Next, I attached the tubing to the board using zip ties. Notice, one end of the tube starts right at the top of the board. The other end of the tube will hang off the board a good 7 or more feet. This long end will be inserted into the screen opening.



The tube will form a U-shape when attached. I have read that this is actually referred to as a U-Shaped Manometer. Makes sense! Note, I drilled more holes at the bottom of the "U" in order to hold the tube in place better.



Continued on next post.

[Doug Miles]

I then picked a "zero" point on each tube, and marked off inches on each side. Here is the finished product, note I have also filled it with water at this point:




Filling with water can be a little tricky. It doesn't take much to go over the "zero" point, and you need to pour out very little before going under the "zero" point. If you will be using this frequently, you might want to add water to get to your "zero" point, and then pour the water into a measuring cup. This way you will know exactly how much water to add the next time.

Now, how to use the manometer. What I did was run the long end of the vinyl tube into the blower fill tube. Make sure the tube runs all the way into the screen. If the tube is not all the way into the screen (and is only inside the fill tube) you might get inaccurate readings. In fact, if I made another manometer, I would probably get 15 feet of vinyl tubing. This picture shows the vinyl tube going into the blower fill tube:




Now all you need to do is turn on the blower. Obviously, you will need to wait until the screen is fully inflated before trusting the water level reading. Also, just a reminder, make sure any deflation/zipper vents are closed at this point.

All that's left is to read the pressure:





From the picture above you can see that the water has gone down 3 inches on the left (the side connected to the screen) and it has gone up 3 inches on the right. When reading a manometer, you will need to add the two. In the case above, the pressure reading is 6 inches (3 inches down on the left, plus 3 inches up on the right).

Also, as I mentioned before, the diameter of the tubing you use does not matter. To test this, I connected a 1/4 " tube along side my 1/2" tube and tested the pressure:




Kind of difficult to see the smaller tube in this picture, but it is connected just inside the larger tube. As you can see, the water level is the same in each tube.

Anyway, this is a great do-it-yourself project. Minimal cost at about $10, even less if you can find some things around the house. But, this is a very powerful tool to have. I will be posting some reviews of blowers shortly, and this manometer will come in very handy. Also, I will be demonstrating how this can be used to determine what the minimum pressure required is for various screens (I define minimum pressure to be the amount required to keep the top cross piece of the frame full inflated). This should help those people who are trying to determine which blower to match with their screen.

Happy manometering!

[Mackinac Movies]

Well I whipped one up using your directions, and it worked out just fine. Mine isn't nearly as nice looking as yours though, but it worked.

I wanted to test if both of my b-Air blowers were performing the same. One take about 30 sec longer to spin up to speed, so I was wondering if it may be bad. So I took both of my CB screens, and tried both blowers. I got the following results:

16x8 screen: Fast blower: working 4"; max 6 1/2"
Slow blower: working 4"; max 7"

20x12 screen: Fast blower: working 4"; max 5"
Slow blower: working 4"; max 5 1/2"

A little variation, but nothing to worry about I guess. Interesting that both screens are about the same working pressure, which I subjectively determined by cracking the zipper vent until the top tube started to buckle, then closed just enough to straighten it.

I also wanted to note, that it does not matter how far the tube is shoved into the screen. I tested with the end of the tube inside the screen, and also the blower tube, and got the same pressure reading.

[Doug Miles]

Wow, I never thought anybody would make one! Glad it worked.

You list PSI for your measurements. Do you mean inches, or did you convert to PSI? I know you can convert from inches of water to PSI, I just don't know how to do it.

[Mackinac Movies]

You are right, no conversion. I fixed my post.