A Pump Rating Curve is defined in terms of the pump flow rate and either Node Depth, Dynamic Head or Well Volume.


The pump rating curve is selected from the pump dialog with no restrictions as to the pump type/rating curve relationship. A rating curve using well volume may be used with a pump rated by dynamic head with no warnings generated. The user is responsible for ensuring these errors do not occur.

 

Pump Flow Rate

Pump flow rate (feet3/sec or metres3/sec). The pump's operating range is limited to the range between the lowest pumping rate and the highest pumping rate regardless of the detected dynamic head. Pump rates will remain fixed at either the lowest pumping rate or the highest pumping rate head until the system returns to the normal operating range of the pump.

Node Depth

The rate of pumping depends on the level of water, ie. depth, in the node being pumped.

For an in-line station, the pump rate is based on the water depth at the pump junction. The rule is as follows:

Pump Rate = Rl for 0 < Y < Yl

                 = Ri Yi < Y < Yi+1

                 = Rh Yh-1 < Y < Yh

For Y = 0, the pump rate is the inflow rate to the pump junction.

Dynamic Head

An in-line or off-line pump that pumps according to the head difference over the pump, i.e. uses a multi point pump curve. The rate of pumping depends on the level of water in the node being pumped.

This type of pump station uses a storage node upstream for a wet well (Multiple pumps with different characteristics may be connected to the same storage node to simulate more than one pump in a pumping station).

The dynamic head difference between the upstream and downstream nodes determines the pumping rate according to a three-point head-discharge relationship for the pump. The operating condition (i.e., on/off) for the pump is determined from the wet well elevation from the previous half-step computation.

If the model detects that a pump is on then its flow is computed from the dynamic head difference based on a linearized pump operating curve as shown below.

The pump's operating range is limited to the range between the low-rate head and the high-rate head regardless of the detected dynamic head. Pump rates will remain fixed at either the low-rate head or the high-rate head until the system returns to the normal operating range of the pump.

Well Volume

An off-line pump station with a wet well. The pump must be supplied from its own wet well, ie. only one conduit must be connected to the node at which the pump is located. The rate of pumping depends on the volume of water in the well.

The program sets the node invert level to -100.

Note that only one conduit may be connected to the node from which this type of pump operates.

Inflows to the off-line pump must be derived from the main sewer system through an orifice, a weir, or a pipe. The influent to the wet-well node must be a free discharge regardless of the diversion structure. The pumping rule curve is based on the volume of water in the storage node.

Wet-well volumes are specified as input data for each pump station: Vl < V < Vh, where Vh is the maximum capacity of the wet well. The pumping rates are specified as input data for each station. The pump rate is selected automatically depending on the volume in the wet-well.

A mass balance of pumped outflow and inflow is performed in the wet-well during the model simulation period.

If the wet-well goes dry, the pump rate is reduced below rate Rl until it just equals the inflow rate. When the inflow rate again equals or exceeds Rl, the pumping rate goes back to operating on the rule curve. If Vh is exceeded in the wet-well, the inflow to the storage node is reduced until it does not exceed the maximum pumped flow.