Article 25: Submersible Pumps (dry or wet?) for Water and Wastewater Applications
A Maintenance Manager of a large municipal waste treatment plant asked me to help with the noisy and problematic pumps for his aeration basins recirculation. Presently, he has an old end-suction centrifugal pumps, with a long segmental shaft, snaking up vertically and connecting to a regular dry motor at the surface floor:
Pumps have been problematic for awhile. Repair is always an option, and, although Bob got the quotes from the repair shops, he was more inclined to replace these old pumps (and hard-to-get parts) with a newer design. He was also interested to look at the "dry submersible" pump options. A dry-submersible pump is essentially a regular submersible pump, used for wet wells, but then modified and fitted with options to run dry. Such submersible pump can then be installed exactly at the same place, in a dry pit area, where the existing regular pump (shown on photo above) was, - an easy, simple and straightforward replacement, with little piping changes, and no need for a long shaft, or the motor itself sitting far away, at the top floor surface.
A regular submersible pump' biggest problem is cooling of the motor. It depends on the liquid in the wet-well to cool the motor, and thus the wet well can not be allowed to run completely dry - some water must be present, to cover the pump to almost the top of the hook, to which the pull-out chain is attached. If such pump is installed at the dry pit, instead of a wet pit, there would be no water to cool it, and the motor would burn up quickly.
Some companies, however, make submersible pumps that "do not need to be submersed", i.e. the can run dry, and the cooling of their integral motor is done by the pumped liquid, via diverting a portion of it to a cooling jacket, designed around the outside part of the motor, as shown on the illustration below.
The illustration above comes from the Flygt Pump product brochure, which brings another point to a discussion. Bob wanted to know who makes such pumps, and what are my recommendations. This is not an easy question to answer. There are many companies that make submersible pumps, so which one to recommend. I decided to do a little study, based on three criteria:
1) Good engineering design with quality manufacturing
2) Customer service and support
I then looked up several pump companies that manufacture submersible pumps: Flygt, ABS, Barnes, Ebara, Polaris, and Hydroflo.
I knew about the Flygt and ABS, as I came across their names and installations many times. I had no problems locating their web sites, getting sales and technical brochures, and finding local representatives quickly. What impressed me about Flygt was not just the name recognition, but quality of publications, the extend of the product coverage, as well as familiarity and fluency of their technical sales staff with the pumping stations auxiliaries, such as: guide rail system, control panels, auxiliaries, float switches and other electronic control options, and more. Flygt people seemed to "speak the application language", and not just selling a pump from a limited catalog. In fact, I got their brochure about submersible pump applications, in a simple, layman language, easy to follow, and easy to learn the terminology. When I got done my study of Flygt product, I was impressed with the company technical know-how, the quality of publication and educational material, and the turn-key approach to the pump application request. They acted more like a solution-oriented company, and not just a sales office, represented a remotely manufactured product with obscure name, and just as little commitment to answer questions.
Barnes Pumps literature was decent, although with a flavor a "good-pump-company" outfit, and not necessarily a flow solution organization. I suppose someone who knows exactly what he or she wants in a pump, and knows how to install it, hook up the floats, fine-tune the switches, etc. will do well with them, but if you have questions, I am not so sure the answers would be just as complete.
ABS pump company is also a known player in the industry, and they manufacturer a variety of pump types, and not only for the water and waste treatment submersible applications:
Ebara had a nice web site as well, but it was not clear if they are focused on the municipal submersible market, or on large vertical and other types of pumps, made in Japan. It looks like their US submersible division is in South Carolina, and large vertical pumps division in Houston, with little integration and independent operation. Their web site did not tell me as much as I wanted to know about the pump specifics, such as performance curves, sectional drawings, and other related technical data, although hopefully it will eventually develop some of these capabilities. Their focus seem to be on selling pumps only, and while having certain knowledge about the supporting systems and controls, their main forte appears to be strictly pumps, with the auxiliaries left to the user or the users contractor.
Another company was Polaris, although I never heard the name before, but listed for reference, since it appeared to be distributed close to my home stage, - in the nearby Alabama. Their 2-page brochure did not tell me much, other then an invitation to quote a pump.
The last company I looked was Hydroflo, which appears to be also a representation of the off-shore low-cost manufacturer, and while their quality is probably fine, there is little information available on any technical issues, such as seal options, motor details, sectional drawings, wet or dry pit options, etc. There was no web site available either, but I was able to obtain a quotation on a 30 horsepower pump via my friend in Chicago, who runs a pump distributor.
With the quote, I went to Bob, and showed it to him. He liked the number, and said it is cheaper then some other companies, that he is more familiar. He then asked a few questions: "Will the spare parts be just as competitive? Where are pumps manufactured and who is in charge? Will they offer an extra warranty? Who makes their motor, and what is the detail of the windings? What are seal options? Where is a bill-of-materials, what are the material options, and where is a Recommended Spare Parts List? Where are the curves and is there a catalog?"
Unfortunately, none of Bob's questions could be answered, and so Bob put the quote just where it belonged - to the waste basket!
The question was, I wondered, is any one of these companies, or perhaps any additional others as well, is "better" then others? No. I could not say that, and the products may well be equally good. But the only way for the user to know for sure - is to be convinced by action.
The lesson here is that, even at best price, if the product quality, support, customer service, spares, documentation, and auxiliaries are not in good shape - a pump company would doubtfully get very far in a today competitive world, where customer service, and problem solving, are the name of the game, and not just a sales, on a phone, or a fax machine. Pump users are looking for the solution of their water treatment issue, - a complete system, and just one of its elements:
We do live in a small world these days, and manufacturers crossing country boundaries is no longer a surprise, as companies search for best prices, and good profits. However, with a reduction in cost, we can not afford to sacrifice quality, and - very importantly - need to maintain support and assistance of customers, - before, during, and after the sale. This assistance does not end with a sale of a product: in fact - that is where it just starts. Follow-up, parts availability, literature, drawings, documentations, instruction manuals, and other help, as needed, with potential system troubles -should that happen - is the stuff that will differentiate the successful companies from the rest.
Send you comments to: DrPump@Pump-Magazine.com
Dr. Lev Nelik, P.E., Apics
Editor, Pump Magazine