Listed
below are the most current frequently asked questions in
relation to use of the Visual Water Designer software.
The questions are broken down into the three main sections
of the software  pumping/hydraulics, standard treatment
units, and advanced treatment units. Questions are updated
as they are received. If you have a question that is
not covered below, please contact
us immediately.


Pumping/Hydraulics
Frequently Asked Questions


When
analyzing the hydraulics of a pipe, three methods for
determining the friction loss are supplied – DarcyWeisbach,
Manning’s Equation, and the HazenWilliams equation.
Which is the most accurate, and is there a better time to
use one equation over another?


In
theory, the most accurate equation is the DarcyWeisbach
equation since it is the only equation that relates its
roughness value (f) to the diameter of the pipe, and also
accounts for the varying regimes of flow. This is
mostly a nonissue, however, since almost all pipes
encountered during a hydraulic analysis exhibit fully
turbulent behavior. The HazenWilliams equation is
still the most popular equation used in practice today
because of its relative simplicity and accurate results.
The Manning equation is typically reserved more for open
channel flow but is also acceptable for full flow pipe
analysis.


In
consulting a few of my engineering reference manuals, I’ve
noticed that there can be some considerable variation in the
K values reported for different pipe fittings. How was
the K value list used in Visual Water Designer compiled? 

This
is a perfect example of the fact that hydraulics is never an
exact science. Many fittings have universal K values,
such as standard bends and valves, but many fitting K values
can vary from source to source. Visual Water Designer's
K value database was compiled from the comparison of
numerous popular hydraulic sources. Visual Water
Designer was programmed with a builtin working K value
database that allows you to change K values for fittings and
add fittings that may not exist in the standard database.
This allows you to tailor the K value database to your
needs. 

When
performing a pumping analysis, there are check boxes
provided for specifying primary sludge or secondary/digested
sludge. If a sludge pumping analysis is being
performed, how does Visual Water Designer account for this? 

Visual
Water Designer will account for the additional friction loss
from pumping sludge by assigning the friction loss a
multiplying factor. This factor is based on the type
of sludge being pumped and the percent solids in the sludge. 

Can
negative suction and/or discharge heads be specified when
performing a pump analysis? 

Yes,
Visual Water Designer will allow the entry of negative
suction and discharge heads. 

How
does the specific gravity of the fluid being pumped affect
the pump evaluation? 

The
fluid specific gravity is taken into consideration when
calculating the maximum vapor pressure at the pump, which is
part of the net positive suction head (NPSH) calculation.
Additionally, the liquid specific gravity affects the
discharge pressure of the pump. 

How
does Visual Water Designer analyze a sewer if the sewer is
flowing full for part of its length? 

Visual
Water Designer uses the open channel standard step method to
start downstream and work upstream in analyzing a sewer
depth. If during the analysis a full flow depth is
reached before the total length of the sewer is analyzed,
the remaining portion that is flowing full is analyzed as a
full flow pipe. 

During
a culvert analysis, the tailwater depth may be specified as
critical depth. Why is this? 

If
the flow exiting the culvert will experience no effect from
any downstream control, such as a drop at the end of the
culvert, the depth coming out of the culvert will be at
minimum energy, which is critical depth. 

Standard
Treatment Units Frequently Asked Questions


For
the BOD reduction analysis in a trickling filter, two
methodologies are available, the NRC equations and the VelzSchultz
methodology. Which should be used and is more accurate?


The
VelzSchultz equations were developed for more modern media,
which is plastic media. The NRC equations are more
widely used and generally accepted for BOD reduction analysis,
but the VelzSchultz equations more accurately take into
consideration the type of media and media characteristics than
the NRC equations. Simply put, for plastic (vertical or
crossflow) media, the VelzSchultz equations are more
accurate, whereas the NRC equations apply more to other types
of media (rock, stone, wood, etc).


For
disinfection, it was noticed that equations exist for the
calculation of the CT product for chlorine, yet equations are
not used for the CT product for ozone and chlorine dioxide.
How are these CT values calculated?


This
is correct, equations have been developed for the calculation
of the CT value for chlorine. Although various complex
equations have been developed for the calculation of CT values
for chlorine dioxide and ozone, tables of CT values are used
to simplify the calculation. These tables are based on the
temperature of the water and the log inactivation desired.
These tables are provided in the theory section of the user
manual.


For
rotating biological contactors, how does the software consider
multiple stages for BOD reduction?


For
BOD reduction in rotating biological contactors, the effluent
BOD is based on the influent BOD coming into the RBC. If
multiple stage RBCs are being analyzed, the effluent BOD from
the first stage is then used as the influent BOD to the next
stage. This procedure is followed until all BOD stages
are analyzed.


Advanced
Treatment Units Frequently Asked Questions


When
evaluating the fluid flux for a reverse osmosis system, if a
solute other than salt is being considered, how does the
analysis differ?


The
osmotic pressure is affected directly by the molecular weight
of the solute, therefore the molecular weight of the solute
must be known. The osmotic pressure in turn affects the
fluid flux through the membrane.


For
a UV evaluation, how does the theoretical UV dose differ from
the required UV dose?


The
theoretical UV dose is the dose applied to the liquid under
perfect conditions. The required UV dose takes into
account other factors that will affect the dose delivered to
the liquid. The factors considered in this calculation
are the lamp fouling factor and lamp aging factor, which can
significantly reduce the dose applied by the UV system.


Other
Frequently Asked Questions


If
an assumption is changed during an analysis, does this
assumption get saved if the file is saved?


Yes.
If an assumption is changed for a particular analysis or
calculation and that file is saved, the updated assumption
will also be saved.


On
the assumptions form, there is an option to “Restore
defaults”. What happens if the default assumptions are
restored?


The
Visual Water Designer software is shipped with a variety of
assumptions that are used in various calculations throughout
the software. The user may change any of these
assumptions at any time. If it is desired to revert back
to the original assumption values shipped with the software,
this option will allow the user to restore those values.
Note that once this is done, any changes that were saved in
the assumptions database will be lost.


I
notice there is a “Specialties” tab but it never seems to
be active. What is this tab used for?


The
Specialties tab was put in the place for the pumping analysis
option. It provides additional calculations for pump
power requirements, affinity laws, and pump operational costs.
This tab will only become active when analyzing a pumping
system.


If
the “Clear” option at the bottom of the design form is
selected, it clears all of the active data from the form.
Does it remove the data from a file with other active
calculations?


No.
If more than one parameter for a particular feature is
analyzed, the clear option will only remove the data for the
active parameter being analyzed.
