One of the most important factors to be studied carefully is the discharge coefficient “Cd" 
through the orifices, which reflects the efficiency of the flow and plays an important role in the design of 
hydraulic units. The purpose of this paper is to investigate experimentally the effect of changing orifice 
thickness on the discharge coefficient for water flow through different orifice shapes and comparing each 
other. To achieve this goal, four orifices shapes were used: circular, square, equilateral triangle and 
rectangular, five different thicknesses (9.25, 7.5, 6.75, 4 and 2 mm) were tested. It should be noted that 
the tests were conducted on four different values of the pressure heads affecting the center of the hole: 
(35, 40, 45 and 50 cm). Bernoulli's equation was used as a theoretical basis for calculating the discharge 
coefficient. 
The results of the study demonstrated that the changing in the thickness of the orifice affects the 
coefficient of discharge. The coefficient of discharge gradually decreases when the ratio (orifice thickness 
“t"/orifice equivalent diameter “d") increases, with the fixity of both the orifice area and the vertical 
pressure head located above the center of the orifice. In all the analytical comparisons made in this study 
it was observed that circular orifices give the highest values of the coefficient of discharge compared to 
all other shapes followed by equilateral triangular orifices and then square orifices and finally it was 
observed that rectangular orifices give the lowest values of the coefficient of discharge.