To assign an Emitter Coefficient for a hydrant:
- Click on the More button from the InfoWater Pro ribbon.
- Choose Specify Emitter Coefficient for Hydrant option to launch the Specify Emitter Coefficient for Hydrant dialog box as shown below.
It automatically calculates the emitter coefficient for the hydrants in the entire network or for the hydrants defined by the GIS selection based on the user-specified hydrant nozzle diameter and orifice flow coefficient. Both US Customary and SI units are supported. A default orifice flow coefficient of 0.9 is assumed.
If the Attribute Table is populated with the nozzle size, which is the size of the nozzle that will be flowed, the ArcGIS function “Select by Attribute” under the Selection menu can be used to select hydrants of the same diameter and assign an emitter coefficient.
Emitter Coefficient - This value is automatically populated based upon the specified orifice coefficient and the nozzle size unless the "Other" option is selected. When "Other" is selected, any coefficient may be entered here and assigned to the specified hydrants.
Orifice Flow Coefficient - Enter the desired value for the orifice coefficient. The value for the orifice coefficient must be between 0.5 and 1.0. This value is used in conjunction with the nozzle size to calculate the emitter coefficient.
Nozzle to Operate - Select the nozzle size that will be used to flush the corresponding hydrant. To set user-defined coefficients, choose "Other".
Apply to Selection Only - The emitter coefficient will only be assigned to selected hydrants when this box is checked. If unchecked or grayed out, the coefficient will be assigned to all hydrants in the hydrant feature class.
OK - Click to save any changes and close the dialog box.
Cancel - Click to close the dialog box without saving any changes.
The Emitter Coefficient, Ce, represents the flow (in flow units) that occurs at a pressure drop of 1 psi (or meter). It can be calculated from orifice analogy as follows:
Where: the flow unit conversion factor, Fc, is equal to 1 for cfs; 448.83 for gpm; 0.6463 for mgd; 0.5382 for imperial mgd; and 1.9837 for acre-ft/day. The orifice flow coefficient, Cf, is found from field experiments (e.g., pitot reading on the hydrant) and normally ranges from 0.6 to 0.9 for most orifices, and the nozzle diameter is expressed in inches (mm). For example assuming a flow coefficient of 0.9, a 4.5-inch fire hydrant nozzle will yield an emitter coefficient of 544 and a 2.5 inch fire hydrant nozzle will give an emitter coefficient of 168.
The emitter coefficient can be manually assigned in the Attribute Browser. The Specify Emitter Coefficient for Hydrant dialog box (see above) can be used to determine the emitter coefficient based on the desired orifice flow coefficient for various nozzle sizes. The flow is expressed in gpm (see above).