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Emitters are devices associated with nodes that model the flow through a nozzle or orifice. In these situations, the demand (i.e. the flow rate through the emitter) varies in proportion to the pressure at the junction, raised to some power. The constant of proportionality is termed the “discharge coefficient”. For nozzles and sprinkler heads, the exponent on pressure is 0.5.

 

Emitters can also be used to simulate leakage in a pipe connected to the node (if a discharge coefficient and pressure exponent for the leaking crack or joint can be estimated). They can also be used to compute a fire flow at the node (the flow available at some minimum residual pressure). In the latter case, one would use a very high value of the discharge coefficient (e.g., 100 times the maximum flow expected), and modify the node’s elevation to include the equivalent head of the pressure target.

 

When both an emitter and a normal output are specified for a node, the demand that is reported in the balanced results includes both the normal output and the flow through the emitter.