At a recent CA Avocado Society meeting there was a discussion about bout flowmeters and their selection. Flowmeters measure the volume of water moving through a full-flowing closed pipe and as such are one of the key components of an irrigation system whether drip, microsprinkler or full pressure systems. They are essential for managing irrigation efficiently and for monitoring the performance of the irrigation system. Managing irrigation efficiently requires: (1) knowing how much water the crop has used since the last irrigation (irrigation schedu7ling); and (2) operating the irrigation system to apply only the amount of water desired. A flowmeter gives the grower the information needed to apply only the amount of water required.
A critically overlooked benefit of a flowmeter is that it makes it possible to identify changes in flowrate during the season (measured at the same pressure), which may indicate problems such as clogging of emitters or filters, leaks in the system or problems with the pump or well.
There are several types of flowmeters and each has their pluses and minuses. Propeller meters are the most commonly used, but can pose two potential difficulties: debris in the water and a small loss of pressure which can be a problem with low flow systems. Alternatives are magnetic meters, ultrasonic, turbine and venture meters. Proper selection is based on pipe size, range of flow and pressure loss. But as with everything it depends on proper installation and maintenance.
Attached is a nice little overview by Larry Schwankl on how to choose a flowmeter for your situation.