In Egypt, most of the newly reclaimed lands depend mainly on drip irrigation systems. The selection of good and appropriate drippers is the first step for successful drip irrigation system design. As well as, the uniformity of water application from drip irrigation system is affected by both water pressure distribution in the pipe network and hydraulic properties of drippers. Therefore, this study aimed to evaluate some irrigation drippers under different operating pressures and spacing on different lateral lengths widely used in Egyptian agriculture. The required hydraulic tests and measurements were conducted at National Irrigation Laboratory of Agricultural Engineering Research Institute (AEnRI), ARC, MOLAR, Egypt. These tests were carried out using 11 drippers of normal (non pressure compensated) and pressure compensated, on line and in line types of drippers with nominal discharges of 2, 4, and 8 l/h. All the drippers were tested and replicated thrice at operating pressure (50 , 75, 100 and 125 kpa), while all the drip irrigation lateral lines tests were at 100kpa operating pressure for treatments of 0.25, 0.50 and 1.00 m dripper spacing on PE lateral lines of 25 , 50 and 75 m lengths and 16 mm diameter.
Results indicated that, for the normal (Non-Pressure Compensated) drippers located at 1m apart on lateral lines of 25, 50 and 75m lengths the emission uniformity (EU) values were 97.45, 96.87 and 85.4%, respectively, when the drippers located on spacing of 0.5 m apart; the EU slightly reduced to 95.5, 95.3 and 81. 5 %, respectively, while, for drippers spaced at 0.25m apart, EU significantly reduced to 90.4, 84.6 and 77.2 % respectively.
For pressure compensated (PC) drippers located at spacing of 1 m apart on 25, 50 and 75m lateral lengths, the emission uniformity (EU) were 97.7, 94.8 and 86.4%, respectively. At drippers spacing of 0.5 m apart; the emission uniformity (EU) were 95.6, 92 and 83.8 % , while at dripper spacing 0.25m apart, the emission uniformity (EU) were 94.4 ,90.3 and 82.6%, respectively. So, emission uniformities of PC drippers were higher than that of normal NPC drippers specially at narrow dripper spacing and/ or long lateral lines.
For friction losses in the 16 mm diameter PE lateral lines of 25, 50 and 75 m lengths with 4 l/h drippers located at spacing of 1m apart, the actual measured friction losses were very close to the values created from theoretical calculation by Hazen -Williams equation using C= 140.