Originally Posted by Jonn
Finally able to access my sump pump, it's a Zoeller 57, 1/3 horsepower. From what I'm reading online it is a solid, well rated pump. But I need to upgrade. With the years of service I got from this pump I'm inclined to get another Zoeller. A Zoeller M98 perhaps?
The way to tell how much of an improvement in flow capacity you're going to get from the larger pump would be to cross plot it's performance curve with a head loss curve for your piping.
Every piping system can be characterized by a chart that compares the pressure (in feet of water) at the pump outlet with flow rate through the piping. Like this:
From the above diagram, you can see that the higher the flow rate through the piping, the higher the pressure you have to have at the pump outlet to overcome friction losses through the piping. ("head" is pressure expressed in feet of water. every vertical foot of water exerts 0.4333 psi of static pressure because 1 cubic foot of water weighs 62.4 pounds, so dividing by 144 square inches at the bottom of that cube yields 62.4 pounds/144 sq in or 0.4333 pounds per square inch per foot of height. So, a column of water 20 feet high would exert a pressure at the bottom of 20 ft X 0.4333 psi/ft = 8.6667 psi gauge)
And, every pump manufacturer tests their pumps to determine it's "performance curve", which shows how the pressure at the outlet end of the pump increases as the flow rate out of the pump is reduced to zero flow, like this:
You can see that the pressure at the outlet end of the pump is at a maximum when the flow rate is zero, (which is what you'd expect) and diminishes as the flow rate is allowed to increase.
The flow rate you'd get with the Zoeller M98 would be determined just by cross plotting the head loss of your sump pit piping with the performance curve of the M98 pump, like this:
The point at which the piping system's head loss curve and the pump's performance curve intersect tells you the flow rate and pressure the M98 pump will operate at when installed in your sump pit.
To just get a ballpark idea of how much of an increase you can expect, simply read off the flow rates for each pump at various "head" values, and use the average percentage increase.
For a more accurate guestimate, phone up Zoeller Pump and provide them with the nominal sizes and lengths of the piping downstream of your existing sump pump, and they should be able to work out approximately what the system head loss curve of your piping should be. Or, you can probably do it yourself by working out the volume flow rates for various upstream pressures (Pressure at "A") at this web page:
Note that the pressures have to be entered in psia or psi absolute, so add atmospheric pressure. In New Jersey, you're close to the ocean and hence sea level, so use atmospheric pressure of 14.7 psi
psi(absolute) = psi(gauge) + 14.7 pounds/sq in
To calculate average velocity from flow rate, simply divide the flow volume by the area of the ID of the pipe. (eg. 10 cubic feet per minute / .05 square feet = 200 ft / minute) In plumbing, the nominal pipe sizes are very close to the actual ID of the pipe, so just presume the nominal pipe size is the actual ID.
Now, this program calculates flow rate based on upstream pressure and "average flow velocity", which, is actually the flow rate divided by the area of the ID of the pipe. So, the answer (flow rate) depends on the input variable (flow velocity), and that means that you have to converge on the correct answer. So, in practice, the way you'd use this program is as follows:
1. For any given upstream pressure (Pressure at "A"), guess a flow rate and determine the average flow velocity by dividing that flow rate by the area of the ID of the pipe.
2. Enter that average flow velocity, and get the computer to calculate the flow rate based on that flow velocity.
3. When the computer calculates the same flow rate as you guessed, then you've converged on the correct flow rate for that pump outlet pressure.
4. Repeat steps 1 to 3 for various pump outlet pressures, and plot a graph of flow rate versus pump outlet pressure (or "head" (in feet of water, psi, kilopascals or whatever units Zoeller's pump performance curves are plotted in)).
For water, use a viscosity of 1.0 centipoise (cP) and a density of 1 kilogram/liter.
For surface roughness, presume it's small enough to be considered zero. That is, the piping is perfectly smooth on the ID. I know it's not, but the effect of pipe roughness is small compared with pressure drop due to flow through the pipe, so we can ignore the pressure drop due to pipe roughness for our purposes.
Account for elbows in your sump pit piping by using the equivalency chart for feet of straight pipe on this web page:
Your local friendly Zoeller sales representative, sales agency or Zoeller pump wholesaler/distributor should also be able to provide the performance curves for your existing pump and the M98.
Plotting both performance curves on the head loss curve for the piping will give you the pressure and flow rate both pumps should operate at when installed in your sump pit, and that will tell you how much of an increase in flow you can expect by upgrading to the M98.