manometer
 

Anyone have experience building one. What size tubing is preferred?

Buy a vacuum guage?

manometers are usually used to test slight pressure variations like for filter racks in paint booths in the hotrod world
your measuring pressure not volume so use a small 1/4'' tubing
set up a U shaped hose on graph paper and use a dyed fluid to check differential pressure
but then you have to worry about how to calibrate it or
you can buy a new manometer from graingers.com for $40 or a used one off ebay for $5
if you buy used make sure you can get the right fluid for it as it will be calibrated for the specific gravity of the fluid

I have a really nice vacuum gauge, but I just like building stuff on my free time. Is it water or thicker viscosity?

Does the amount of vacuum/pressure change what thickness of fluid should be used

distilled water
 

The guages are often read in "inches of water" - the depth of the "U" tube has to be something over 30 inches I believe. I've seen 1/4 and 5/16 aquarium type tubing used to make the "U".

One tube is exposed to atmosphere (with no air flow over the open end) and the other end exposed to the pressure you are testing - it is a comparitor device. You want to measure the difference in the height of the water on both sides of the "U".

Just make a “U” tall enough to cover the pressure range you expect without blowing the water out. The dia. of the tubing does not matter; use clear Tygon tubing from the hardware store, I like 3/8”. Hook up to the pressure you want to measure, just take a tape measure and measure the difference in height between the two columns of water, that will be your pressure (inches of water pressure). 1 inch of water @ 60 deg F = .0361 psi .

You can add some food coloring to dye it if you like.