The Irrigation Training & Research Center (ITRC) of Cal Poly San Luis Obispo tested 28 different pressure-compensating models of microirrigation emitting devices from a total of nine manufacturers in order to compare independent laboratory testing with manufacturer specifications.

The test results indicate that:

The majority of ~0.5 gallon-per-hour emitters (drippers), regardless of manufacturer exhibited:

1. Good uniformity of manufacturer

2. Had excellent response to pressure variation

3. Had consistent flow rates within the nominal operating pressure range

    

   But that the percentage of well-performing products decreased as the designed flow rate increased. Many of the emitters designated as microsprinklers or sprayers, although pressure compensating did not compensate at the normal operating pressures. Often the pressure compensating feature did not start performing until much higher pressures were achieved. Often this occurred when clogging occurred and this clogging often occurred where the pressure diaphragm was located and was not performing. Sediment would get in back of the diaphragm.  Effectively the emitters were not pressure compensating. The testing procedure of numerous medium and high flow models also found individual pieces were found to be defective. These faulty emitters had a measurable effect on the evaluation for those models.

   Read more at: http://www.itrc.org/reports/pdf/emitters.pdf