When going down the rabbit hole of gasification most people come to a point where they want to measure the amount of gas they are making.  This is not a hard thing to do but we are often dealing with a hot, tar laden, dirty gas.  This isn’t very friendly to most devices.  I certainly wouldn’t flow wood gas through my $1200 Omega rotameter.  Just the glass explosion hazard in a sneeze is enough to stop me.  The better way to measure flow is with an orifice restriction plate.  Since many people have trouble with welding I thought I would build a weld free device that is heat resistant and easy to clean if it gets dirty.  Here it is:

It is just a pair of 1″ tee’s with a 3/4″ close nipple bushed in the middle.  The 1/8″ pipe extensions are to keep the manometer from melting if it is operated with hot gas.  Their length is not important.

The clear tubing is a “U” shaped water manometer to measure the pressure drop across the close nipple acting as a restriction.  To measure the gas flow through the device, measure the difference in water column heights in the manometer and use the calibration chart below:

 

I would not trust this device to four decimal places but it is a cheap, effective way to tell you what is going on in your system.

Notice that the calibration curve does not go through zero inches of water at zero flow.  I would not trust the device below roughly seven cfm of flow.