Pump Head Loss Calculator – Easing System Design

One thing that aquarists have to deal with when
designing a new system or reconfiguring an existing system is flow. Part of
that overall question is selecting the proper plumbing configuration and
selecting a pump for the application.

For the last couple of years there have been online applications that
allow an aquarist to enter their plumbing configuration and select a pump
to see what kind of flow they would get with their proposed plumbing
schematic. A couple drawbacks to the online applications are that they
don’t allow you to add new pumps and you can’t save your results after
selecting a configuration and running a calculation. Because of the
deficiencies (and wanting to delve further into programming), I wrote a
program that will allow you to do just that. It is written in the Python
programming language and has been open sourced under the GNU General
Public License
for others to contribute to in hopes of making it
better. For those of you who don’t know what open source software is,
it’s:

“…computer software whose source code is available under a license
(or arrangement such as the public domain) that permits users to study,
change, and improve the software, and to redistribute it in modified or
unmodified form. It is often developed in a public, collaborative manner.
It is the most prominent example of open source development and often
compared to user generated content.” (1)

There’s all sorts of open source software available (Sourceforge.net, Google Code, etc) if the reader has
never heard of it before.

For those interested in the source code, it can be found on Google Code.

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This article will not go over pumps and plumbing design as it was
already covered in great detail by Sanjay Joshi, Ph.D. and Nathan Paden in
An
Engineering View of Aquarium Systems Design: Pumps and Plumbing
.” (2)
It will, however, go over installing, using the program, and adding
additional pumps to the pumps list.

Download and Installation

Download
the program and install it in the normal manner. Currently only a Windows
installer is available. If you’re using an alternative operating system
like Linux, you will need to install Python 2.4, Tix, and BeautifulSoup
before going further. If there is someone out there with Linux expertise
that would like to build an installer for Linux (Ubuntu, Fedora Core, etc)
email me or submit it on the project
site and we can work on it.

Usage

Once you’ve downloaded and installed the software, double click on the
icon to start the program. Below is what you’ll see:

plumbingpy.jpg

The program entry fields.

To use it, all you have to do is select your pump from the dropdown
list, followed by your pipe diameter. Next enter all of your plumbing
variables and click the “Solve” button. The results will be printed at the
bottom of your screen. You’ll be shown the Head Pressure (ft loss), Head
Pressure in pounds/inch (psi), the resulting Flow Rate your system in
gallons/hour (gph) and the Exit Velocity of the water coming out of your
exit pipe. The program is smart enough that if you tell it that there is
more than one Exit in your plumbing diagram, it will divide your water
velocity by the number of exits and tell you the exit velocity per plumbing
exit. Current limitations of the program are that you cannot select more
than one pipe diameter. Multiple pipe diameters make the calculations
significantly more complex. The program does assume that you know something
about the various pumps when trying to find one for your application.
Currently there are over 120 pumps in the database so having a bit of
knowledge of the pumps and what they can do beforehand is a plus otherwise
you may be selecting a lot of pumps before you find one to your liking.

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As mentioned, there are two nice features to this program:

  1. You can save your results
  2. You can add your own pumps

Saving your Data

This is pretty straight forward. Go to File – Save and enter the
filename you want to save your data as on the filesystem. The program saves
your files to a .csv format. .csv is a very simple format that can be read
by just about all spreadsheet programs. It can be opened in Excel,
OpenOffice Calc, etc. It makes it very handy when you’re trying to work
through multiple plumbing configurations and you want to compare them.

How To Add New Pumps

Adding new pumps to the program is a straight forward process. It can be
a bit involved up front as you’ll have to do a bit of leg work to find the
pump curve for the pump(s) you want to add to the program. Then it’s a
matter of converting that curve into a series of constants that describe it
mathmatically. After that it’s as simple as editing a text file.

The steps to add a pump to the program are as follows:

  1. Obtain a pump curve for the pump you want to add
  2. Recreate the pump curve in Excel and draw a 3rd degree polynomial
    through the data set
  3. Extract the polynomial constants from the equation
  4. Edit pumps.xml (located in your program folder) and add the
    constants.
  5. Restart the program

Obtaining the Pump Curve

The first step is to obtain the pump curve for your pump. Sometimes it’s
as simple as doing a Google search for the pump and finding the associated
pump curve. Other times you may have to resort to emailing the manufacturer
for the pump curve. A lot of it will be digging on your part.

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There was a request in a forum
post
for the Oceanrunner OR series of pumps. The poster included the
technical details for the pumps as well as the pump curves for each pump.
For this example, I will use the Oceanrunner OR 6500 pump and the technical
details for this pump can be found in the following specification:

oceanrunner-or-pump-curves.jpg

Oceanrunner OR pump specifications.

At the very bottom of this specification sheet is our pump curve. It’s
the blue shaded graph that has plots l/h vs. m.

Now that we have the pump curve in our hands, the next step is to
recreate the pump curve in Excel or any other spreadsheet that can be used
to draw lines through data points.

Recreate the Pump Curve

In this example, I’ll use Microsoft Excel for recreating the pump
curve.

Start up your spreadsheet program. The pump curve for the OR 6500 is
given in meters vs liters/hour. Basically what we are going to do is
extract six data points from the chart and make a table out of it. At six
different points on the pump curve, extract the meters and liters/hour
values and enter them in your table. The below graph shows our
datapoints:

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curve-with-data.jpg

The OR 6500 pump curve with our data points
extracted.

When done you should have a table that looks something like this:

Oceanrunner OR 6500
meters liters/hour
0 6500
1.6 4000
2.25 3000
2.8 2000
3.4 1000
3.8 0

Now we have to do a bit of math. In order to obtain our pump constants,
we need our data to be in feet vs. gallons/minute. The following are the
conversions from one unit to another:

  • 1 meter = 3.28083 feet
  • 1 gallon = 0.2641721 liters
  • 1 hour = 60 minutes

Using these conversion factors, our table will now look like this:

Oceanrunner OR 6500
feet gallons/minute
0.0 28.6
5.2 17.6
7.4 13.2
9.2 8.8
11.2 4.4
12.5 0.0

Now that our data is in the proper format we will graph it to find our
pump constants. First, select the region that contains the data points:

select-data-points.jpg

Selecting our data points.

Create a graph by either clicking on the Chart Wizard icon in your menu
toolbar or by clicking on Insert – Chart menu selections. The Chart Wizard
should start up. Select the XY (Scatter) option from the Chart Type
selection box and then click the Next > button. Click the Next >
button until you get to the place where you can enter a Chart Title, Values
(X) axis, and Values (Y) axis. Enter your title as “Oceanrunner OR 6500”,
y-axis as “Gallons / Minute”, and your x-axis as “Feet”. With that done,
click the Finish button and your chart will be created for you. You’ll now
have a chart that looks something like:

chart-with-data-points.jpg

Chart with the proper data now displayed.

Next, we need to plot a line through the data in order to obtain our
pump constants. Click on one of the dots on the chart that was just drawn
and then right click and select “Add Trendline” from the menu. In the Type
tab, select “Polynomial” and increase the “Order” from 2 to 3 in the box
beside it. Now click on the Options tab of that window and check the
“Display equation on chart” and click OK. A 3rd degree polynomial is now
displayed on your chart. Right click on the equation and select “Format
Data Labels.” On that window, select the Number tag and in the Category
box, select Number and increase the Decimal Places from ‘2’ to ’10’ and
click OK when done. Now we have a line equation that describes our pump
curve. From this we can easily pull out our pump constants.

The line equation should loook something like:

y = ax^3 + bx^2 + cx + d

From this equation we can easily extract our pump constants.

chart-with-line-equation.jpg

The resulting graph with the line equation on it.

Now we will actually add our pump to the list of pumps that is
selectable in our program. Open up Windows Explorer and navigate to where
you installed your Calculator (default is C:Program FilesPump Head Loss
Calculator) and open pumps.xml in a text editor like Notepad. Scanning
through the file you’ll see a lot of:

<pump name="Mag24">

    <a>-0.004946242991993064</a>

    <b>0.1253160569978384</b>

    <c>-2.761630952530459</c>

    <d>40.04301814394783</d>

</pump>

What we are going to do is copy a section and add our pump name and pump
constants to the appropriate places.

If you look over the code in the file you’ll see it’s pretty straight
forward. Every pump is defined within a <pump /> tag in an attributed
named (obviously) “name”. Our pump constants can be found nested inside
this tag in <a />, <b />, <c />, or <d /> tags.

A short <info /> tag is placed at the very beginning of the
pumps.xml file in order to remind anyone adding pumps to the list exactly
how it should be done. It’s there as a matter of convenience so that you
don’t have to refer back to this article to remember how to do it.

Copy a <pump /> section and paste it right below the last pump in
the list. Now, edit the “name” attribute by replacing the text within the
quotation marks with “Oceanrunner OR 6500”. Now, edit each of the <a
/>, <b />, <c />, and <d /> tags and place the
appropriate constants within each tag. “a” represents the constant in from
of x^3, b represents the constant in from of x^2, c represents the constant
in from of x, and d represents the constant at the very end of our
equation. If there is a negative sign in front of a constant, make certain
to add that in as well. Make certain that you have no extra spaces within
your <a />, <b />, <c />, or <d /> tags as this
might throw an error in our program.

Below is what your addition should look like:

<pump name="Oceanrunner OR 6500">

    <a>-0.0060752490</a>

    <b>0.0833654927</b>

    <c>-2.3785723842</c>

    <d>28.6266386098</d>

</pump>

Once that is done, save the file and re-run the Pump Head Loss
Calculator. With any luck your pump will now be added to the list.

Conclusions

I hope that you enjoy the program. If you happen to add new pumps to the
program, by all means contribute those pumps on the project page at Google
Code. Please submit bug reports, code fixes, suggestions, etc to the
project as the users will make this a better program overall.

Enjoy!

References

  1. Open-source software, Wikipedia, http://en.wikipedia.org/wiki/Open_source_software
  2. An Engineering View of Aquarium Systems Design: Pumps and Plumbing by
    Sanjay Joshi, Ph.D., Nathan Paden, and Shane Graber, Volume 2, Issue 1,
    Advanced Aquarist’s Online Magaine (http://www.advancedaquarist.com/issues/jan2003/featurejp.htm)
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 Shane Graber

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