Submersible Pump
Submersible Pump
(OP)
On one of our facilities we have an influent well fed by force main with discharge handled by a submersible pump. The pump wears out frequently due to running too much. From the elevation at which the pump takes in influent to that elevation at which the influent discharges downstream is 4'.
The pump in question is spec'd to require 12' of head on the discharge side. It is thought that by adding pipe to create the 12' of head needed, the pump would then operate in an efficient manner and would not wear so quickly.
Two questions arise from the proposed solution:
1) Is the solution plausible?
2) Or, would it be possible to find a pump that would operate in the given situation with only the existing 4'elevation change?
Thanks for any comments, questions, suggestions, etc.
The pump in question is spec'd to require 12' of head on the discharge side. It is thought that by adding pipe to create the 12' of head needed, the pump would then operate in an efficient manner and would not wear so quickly.
Two questions arise from the proposed solution:
1) Is the solution plausible?
2) Or, would it be possible to find a pump that would operate in the given situation with only the existing 4'elevation change?
Thanks for any comments, questions, suggestions, etc.





RE: Submersible Pump
Richard A. Cornelius, P.E.
WWW.amlinereast.com
RE: Submersible Pump
Adding unnecessary head to a pump will not make the pump more efficient, it will make the pumping inefficient.
RE: Submersible Pump
Also you should analyze the design storage depth in the wet well. This is the depth between the top of the pump motor (Pump Off" elevation) and the elevation of the "Pump On" float switch. Pumps that come on too frequently could be due to not having enough storage depth in the wet well. A deeper storage depth yields less pump activation.
Do you have any vertical flexibility to adjust the "Pump On" float switch elevation? If the "On" elevation can be raised, this will increase the storage depth to minimize pump cycling time.
Also some pump manufacturers have pumps that can allow the motors to be exposed to air for specified periods of time. This allows you to lower the "Pump Off " elevation and thus increase the storage depth.
Finally, if your pump is running for extended periods of time, it could be that it is undersized to remove the design flows efficiently. A pump with higher HP and speed will evacuate the wet well quicker and maximize the storage fill duration time and thus reduce the frequency of pumping. Proper pump sizing needs analysis of these factors:
1.TDH or Total Dynamic Head
2.The Hydraulic slope (Hazen Williams equation)
3.Friction loss
4.Expected flows
5.Wet well diameter
6.Manufacturer's pump performance curves
These are the things I would look at first.
RE: Submersible Pump
What is the cause of failure?
The only way running to much can cause a failure is if you are pumping abrasives. Are the impellers and shaft worn from abrasives?
Not enough head can cause a failure from upthrust. Are the impellers worn out on the top side?
Cycling on and off to often can cause a broken shaft, stripped out coupling, loosened impellers, overheating of the motor, and other problems. Does the motor burn up or does the pump just wear down and stop moving enough fluid?
Determining the actual cause of failure can help you find the solution.
RE: Submersible Pump
http://virtualpipeline.spaces.msn.com
RE: Submersible Pump
1) Axial flow will collects rags too easily
2) Pump suppliers are not much help with this since the configuration demands a low head/high discharge pump and there do not seem to be many, if any, of these that will work for the situation.
3) The well does have two pumps in it and both would be replaced should we find the appropriate type available.
4) I beg to differ in regard to pumps not wearing out from running too much. On wastewater facilities pumps are replaced continually from the incredible variety of matter flowing through the pumps. The combination of running continually and abrasives does them in quite well.
Our need and request is simple, to find a quality low head/high discharge pump that will operate continously for long periods that will handle abrasives.
RE: Submersible Pump
http://virtualpipeline.spaces.msn.com
RE: Submersible Pump
RE: Submersible Pump
Regarding your comments re the pumps "wearing out" -it stands to reason that if you are pumping solids etc you can expect the pumps to "wear out"- the secret is to find pumps that are designed to handle abrasive materials and give you the pump performance required,
What is the flow rate for these pumps, this will assist in making some meaningful comment and what pumps do you have installed at the moment?
RE: Submersible Pump
The solution to the abrasives may be twofold. Better screening and better quality impeller and casing.
Solution to the pump curve issue may be to throttle a valve, reduce the size of the discharge line or to replace the bearings with something a little beefier that can handle the thrust.
RE: Submersible Pump
RE: Submersible Pump
For abrasives, you can get impellers designed for abasives (such as ceramic coated impellers). They cost more; but, will last longer.
If you can't find a pump with a good curve, you can throttle the flow as CVG stated. A good valve for this is a pinch valve as it will not have protruding edges to catch material when it is partially closed.
RE: Submersible Pump
First off, do you have a pump protector. (Franklin electric makes a good one)
Second, an axial flow pump is what you should probably look into. (Grundfos is what i recommend for all my clients)
And on top of that is your pump operating in its efficiency peak?