Spud Wiki wrote:Needle Valve plus Pressure Gauge
Another type of fuel meter is simply a needle valve and a low range pressure gauge. The needle valve can be the valve and very small outlet hole in a typical Bernzomatic torch head.
The needle valve is plumbed to the chamber as is the low pressure gauge. To protect the torch and gauge it is a good idea to plumb both through a single small ball valve. To use, the ball valve is opened. Then the needle valve is opened a small amount. When the pressure in the chamber has risen 4% the two valves are closed. Assuming an atmospheric pressure of 14.7 PSI, adding 4% propane will raise the pressure in the chamber by 0.59 PSIG. Since the pressure rise is small, standard 120 or 250 PSIG gauges won't work for this type of meter.
A possible replacement for a low pressure range gauge is a "U-tube manometer". In this type of pressure gauge the pressure is related to the difference in height of the two columns of liquid. If the U-tube is filled with water, then a 1" difference in height represents a 0.0361 PSI difference in pressure. So, 0.59 PSI would be a 16.3" height difference for the two water columns.
link (scroll to bottom)
Measuring propane seems easy enough, as the article says you need 16.3" height difference.
Has any one used a U tube manometer to fuel a hybrid? I haven't found anything searching Google images, using the parameter site:spudfiles.com, or using the search here on spudfiles.
And the wild idear...
If you wanted to measure 45 psi in a 1:1 ratio manometer it would need to be very tall. So I was thinking what if the side exposed to the atomsphere was a 4" pipe, and compressed air side was 1/8" ID tubing. With that big difference in ratio will that destroy the accuracy? Basically should I just use a pressure gauge like a regular person? Would it even work as I intend?