Hydraulic Engineering Tutorials:  Orifices in Series

Often we need to combine orifices in series to arrive at a restriction that would be prone to plugging. As a general rule, we try to avoid orifices smaller than about 0.02 inches in diameter because of the danger of contamination. The following example allows you to input two diameters and find the equivalent single diameter orifice.

We will use the familiar sharp-edged orifice equation for hydraulic oil:

Q =  25  * A * SQRT(∆P)

dia1 =    0.025    (inches)             area1 =     0.000491    (inches)
dia2 =    0.02    (inches)             area2 =     0.000314    (inches)

Q =    1    (gpm)

∆P1 =    6647    (psi), pressure drop
∆P2 =    16228    (psi), pressure drop

∆Ptotal =    22875    (psi), total pressure drop through two orifices in series

From this total pressure drop we can find the equivalent single orifice:

areaequiv =    0.000264    (in^2)

diaequiv =    0.0184    (in)

Exercise:
Insert various combination of dia1 and dia2 and observe the results.