Fixed Discharge Pumps

A fixed discharge pump is represented as a link of zero length, forming a head-discharge relationship between two nodes. The boundary condition between the link and a node is that of equal water levels. The pump switch-on level determines when the control first comes into operation; the pump will continue running until the upstream water level drops below the lower switch-off level.

Flow Characteristics

The governing model equation assumes a fixed discharge monotonically. Therefore, for any head the following equation applies:

Q = Qf (1) where: Qf is the user defined discharge (m3s-1)

The pump link connects two nodes representing the water level upstream and downstream of the fixed discharge pump; the discharge will be identical at each node on convergence of the iteration. If the upstream level is below the switch-on level (for instance the pump is off), then QFIX = 0.0, DQ1 = ERR, DQ2 = ERR. Intermediate values are linearly interpolated from the table. The discharge corresponding to a head outside the bounds of the table is fixed at the maximum capacity.

The simulation engine updates the pump status every major time-step. If, at a minor timestep, the pump status is on but the upstream level drops below the switch-off level, an intermediate switch-on state is entered; this conserves volume.