A series of Warning messages in AFT Impulse.

There are several different versions of this warning message that may occur when using a Standard Pump Curve (SPC) rather than a Four Quadrant Pump Curve (4QC). These include:

• Pump X is using a Standard Pump Curve and had reverse flow. Head rise and power for negative flowrates were estimated using zero flow values. Predictions after reverse flow may not be reliable. A four quadrant model may be appropriate - see the Help Topic "Four Quadrant Data Set Selection" for details. This warning indicates that the pump junction is using a SPC and saw reverse flow. In that case the pump performance was estimated using the values entered for zero flowrate. This estimate may be acceptable when small amounts of reverse flow are seen through the pump. When reverse flow is present for longer durations or with larger magnitudes, the user should strongly consider using a 4QC to model their pump.

• Pump X is using a Standard Pump Curve and head rise was negative. A four quadrant model may be appropriate - see the Help Topic "Four Quadrant Data Set Selection" for details. This warning indicates that the head rise across the pump junction was negative, either in the Steady-State solution or during the Transient Simulation. This behavior might have happened due either to the upstream and downstream pressures being set incorrectly, or to the pump operating far enough to the right on its curve that the head rise was negative. For centrifugal pumps, this behavior is only allowed if the "Allow Negative dP" Advanced Parameter in the Advanced Parameters Panel has been set to "Yes".

• Pump X is using a Standard Pump Curve and head rise was predicted as negative and set to zero. A four quadrant model may be appropriate - see the Help Topic "Four Quadrant Data Set Selection" for details. This warning indicates that the head rise across the pump junction was predicted to be negative, but set to zero either in the Steady-State solution or during the Transient Simulation. This behavior could have happened due either to the upstream and downstream pressures being set incorrectly, or to the pump operating far enough to the right on its curve that the head rise was negative. Users should examine their pump input including pump curve data, pump curve fit, and pump curve reference density to ensure correct pump performance calculations. Fixing the head rise to zero in this situation is the default behavior of AFT Impulse. Users can allow the head rise to go negative by setting the "Allow Negative dP" Advanced Parameter in the Advanced Parameters Panel to "Yes". Positive Displacement Pumps will never see a negative head rise set to zero.

• Pump X is using a Standard Pump Curve and power was negative.  A four quadrant model may be appropriate - see the Help Topic "Four Quadrant Data Set Selection" for details. This warning indicates that the power requirements for the pump were estimated as negative. Users should examine their pump input including pump curve data, pump curve fit, and pump curve reference density to ensure correct pump performance calculations, and consider using a Four Quadrant Pump Curve if possible.

• Pump X is using a Standard Pump Curve and flow exceeded End of Curve. If no End of Curve was specified, this is the largest entered flow. (Y gal/min, Z seconds) The head or power curve does not close the quadrant. Check the curve data at the calculated flows. A four quadrant model may be appropriate - see the Help Topic "Four Quadrant Data Set Selection" for details. This warning indicates that not only is the flow through the pump past either the End of Curve setpoint or the last data point for the curve that the user has entered, but that the curves increase unbounded as flow increases rather than crossing the zero head axis (x-axis) and staying there. In the transient simulation, the time listed is the first time that this End of Curve value is exceeded. The pump may operate past this point later in the simulation as well. Note that if the pump is operating at a speed other than 100%, Impulse will apply the Affinity Laws to the End of Curve or last data point entered for the pump at 100% speed. Thus, this warning can be generated at flowrates lower than the specified End of Curve if the pump is running at low speeds. Users should check the pump performance both during steady state and the transient simulation to ensure that the pump is only operating on the portion of the curve prior to the flowrate where head and power begin to increase again. Alternatively, users could return to the Pump Configuration window and update their entered data or curve fit such that the head or power curves close the quadrant.