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Posted:
Tue Jul 13, 2004 9:46 pmby rob
Why not use a Vacuum Gauge instead of a Manometer?
Anyone who works on motor vehicles probly has one laying around
Posted:
Tue Jul 13, 2004 11:01 pmby SWB
I've done that, but you need a lot of test depression to make the gauge really useful. Remember the gauge reads in inches of mercury and not water.
SWB
Posted:
Wed Jul 14, 2004 8:16 amby bruce
A water column manometer can be made extremely cheap (some clear tubing and a yard stick or scale of some kind) and gives a finer resolution of your static pressure than a gage does. You don't have to have $100's of $$$ worth of gages to do build a flowbench.
There are users on this site that have built a flowbench for next to nothing and then there are some who have spent hundreds of $$$'s on what they built its all the level at which you want to "play" at 
Posted:
Mon Jul 19, 2004 8:59 pmby 84-1074663779
I am completely with Bruce on this. twenty eight inches of real water is going to read the same, today, tomorrow, and fifty years from now. Your pressure gauge probably will not read exactly the same as anyone else's, especially after you drop it a few times.
A pressure gauge might be tweaked so it reads correct at 28", but reads wrong at 20" and 35". Water manometers do not have this problem either. Water is fairly cheap too......
Posted:
Mon Jul 19, 2004 10:53 pmby Terry_Zakis
Agreed. For low pressures, the manometer is the way to go. Wallace & Tiernan makes pressure gauges, and differential pressure gauges that have 0.06% accuracy across their range. The way they do it, is that each gauge has a custom face place, which is "plotted" to match the calibration standard across the range. They also cost around $1,300 new for the larger 1500 series gauges. So for the low pressure differentials, the manometer has several advantages.
Posted:
Tue Jul 20, 2004 8:48 pmby 84-1074663779
Another problem with mechanical or electronic pressure gauges is that if you overpressure them, they often do not return exactly back to zero. There can also be temperature effects with these as well.
One day a rag or something is going to get sucked into what you are testing. The fluid in your manometers is going to disappear into the bowels of your bench, or hit the roof. Your very expensive laboratory calibrated pressure gauge will probably never be quite the same again.
Water manometers are great, for higher pressures you can always use something more dense, like mercury. Sure it is poisonous, but so is gasoline.