Cliff,

Thanks for your response. Admittedly, this is why we have referred you to hydraulic texts for more in depth answers. But the emitter equation "C" does have units as noted above.

Q = C * p^g so by rearranging we find C = Q/p^g

From the equation Q (units of Length^3/time or Flowrate units) and p^g is (pressure units)^g so C is in Flowrate/pressure unit^g power or is g = 1/2 then it is in units of Flowrate/pressure^1/2.

As I can't find a derivation of where the emitter equation comes from to verify the C used, all we can do is verify the units shown in modeling texts regarding use of emitters like the EPANET helpfile that for emitters is essentially repeated in the Innovyze H2OMAP Water and InfoWater help files.

From the Orifice equation which does use Cd (the coefficient of Discharge) (Pulling this equation from this website: http://engineering.wikia.com/wiki/Orifice_equation)

The

**orifice equation** describes the rate of flow of liquid through an orifice.

The equation can be represented as:

where Q = flow (cubic metres per second)

C(d) =

coefficient of discharge
A = area of orifice (square metres)

g = acceleration from gravity (9.81 m/s^2)

h = head acting on the centreline (m)

So the Cd rearranging is Q/(A*sqrt(2gh)) and noting Length as "L":

now G is in L/time^2 and if H is in L the sqrt (2gh) term is sqrt(2*L/time^2 *L) or sqrt (2*(L/time)^2) which is just units of L/time.

Area is in units of L^2 so the denominator is L^2*L/time or L^3/time which is the same unit as flow and causes Cd to be dimensionless as noted.

A such that seems to show that the "C" in emitter equation is thus not the same Cd in the orifice equation as one has to have units ("C") and one has to be dimensionless ("Cd").

For modeling purposes, regarding what is entered in the model, you are asked to enter the "C" value from the emitter coefficient and not the Cd value.

Hope this helps.

Patrick