Hydratec Inc.

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Standalone HydraCALC (Location)

Error Type: Hydraulic Calculation - Error


During running your calculation, and after receiving the summary regarding your safety margin, you get a similar error.

You'll then likely get these errors, up to 3 times.


Be aware these windows may be BEHIND the calc window, so move the calc window out of the way if it looks like it has crashed or is hung




System is flowing more water then can go through the backflow valve (e.g. system demand 1000 gpm, mfg's curve for that size ends at 900 gpm.


Next larger size valve should be used, a different backflow preventer or enter the curve as a fixed pressure loss. 


Instead of using a fitting curve to have the program figure the curve (ie. Fva), enter the value as a fixed friction loss .  For example, a 10psi loss would be entered as 10#


If you notice the demand gets higher each time you raise the pump's flow rating, this means a loop bypass was connected


Ensure no reference points are repeated between the city & pump, and pump to riser.


This may happen when a curve fitting (ie. backflow) is entered between the pump and the city supplies.  Although the ACTUAL system demand is less than the max flow for the backflow, you may still get this error because the pump's demand could be over the max of the backflow.

In this example, the Q4 value on the pump is 1750 gpm…


This 8” Zwe backflow (Watts 757) maxes out at 1610 gpm …


The Zwe is used after PI (pump inlet) and before the TEST (city connection)


The actual system demand is ~1240 gpm, but this error will pop up;


So even though you’re not really flowing more than 1610 gpm through here, it’s initially comparing the hard numbers and saying 1610 gpm can’t accommodate the potential of 1750 gpm, so I won’t go through with the calculation. 


Rather than using the curve here, check the cut sheet of the backflow and enter the pressure loss as fixed.  For instance, the pressure loss here is 6psi so use 6# (to represent 6 pounds).

[Thanks Sean C]


A custom backflow preventer curve was created that does not start at 0 gpm.


A pressure loss curve for a valve must start at 0 GPM - edit the curve to start at 0 GPM (see "entering a chart loss" in the help menu

Updated: Sept. 18, 2022, 1:05 p.m. Created: Dec. 18, 2020, 8:21 p.m.