Modeling a Connection to an Existing Water Main

If you are unable to model an existing system back to the source, but would still like to model a connection to this system, a reservoir and a pump with a three-point pump curve may be used instead. This is shown below:

The reservoir simulates the supply of water from the system. The Elevation of the reservoir should be equal to the elevation at the connection point.

The pump and the pump curve will simulate the pressure drops and the available flow from the existing water system. The points for the pump curve are generated using a mathematical formula (given below), and data from a fire flow test. The pipe should be smooth, short and wide. For example, a Roughness of 140, length of 1 foot, and diameter of 48 inches are appropriate numbers.

Please note that it is ALWAYS best to model the entire system back to the source. This method is only an approximation, and may not represent the water system under all flow conditions.

Qr = Qf * [(Hr/Hf)^.54]

Where:

Qr = Flow available at the desired fire flow residual pressure
Qf = Flow during test
Hr = Pressure drop to desired residual pressure (Static Pressure minus Chosen Design Pressure)
Hf = Pressure drop during fire flow test (Static Pressure minus Residual Pressure)