Desubmerge Your Submersible

May 5, 2010

A few decades ago, I introduced a contractor to electric-powered submersible pumps. The crew’s first reaction was, “You’re going to throw that electric motor in the water? You’ve got to be crazy!” After a few weeks of getting comfortable with the “subs,” all workers were handling them as though they were born to.

In the years since, submersible pumps or “subs” have become commonplace at construction job sites, in residential basements, in plants, in backyard ponds and at innumerable pumping locations throughout the world. The reason is that subs are all push and no pull. No suction hoses are required. The only weakness that subs have is heat tolerance; however, as long as air or water is going through the pump case, the oil bath-cooled mechanical seal—now usually made of tungsten carbide or silicon carbide—will live.

Sub Advantages
This compact, simple design has more applications than most people are aware of, and not all involve submergence. Besides being used in the typical sump pump configuration, subs can be used as “out-of-water” in-line booster pumps, mixing pumps, aerators and agitators. They also can be used as the “wet” component of a vacuum-primed, dewatering or bypass system, either singularly or in multiples, in parallel or in tandem.

As part of a vacuum-primed dewatering or bypass pumping system, submersibles fit into tight places where other pumps will not go—and up to 15 horsepower can be put there by hand. As one of the three primary components of a dewatering or bypass system pumping station—the wet, “dry” or priming pump—and the air-water separator, the sub is the wet pump handling the groundwater or effluent.

Subs can pump in any orientation, either lying on the ground on their side, standing up or even upside down. Lying sideways makes the pump easy to manipulate by hand. Subs can be outfitted with suction and discharge adapters with grooved restrained-joint connectors so that the pump can be slid into a piping line without moving the piping. In that way, if the pump has to be taken out for service or repair, another pump can be dropped immediately into that position without reconfiguring the plumbing and without a hoist or machine. To protect floor finishes from vibration or scuffing damage, a polyethylene or polypropylene sheet can be placed under the pump.

Using a suction manifold and a discharge manifold allows multiple pumps to be used in parallel. Being electric-powered, these pumps can be controlled by sensors or floats so that as the flow requirement increases or decreases, more or fewer pumps can be brought online or dropped offline automatically.

With the addition of communication hardware (e.g., a mobile phone), if a malfunction or change in status occurs, any number of persons can be alerted automatically. Transmitters also can relay pertinent information, such as flow rates, component temperatures, system vacuum levels or discharge pressures, continuously or at predetermined reporting times to a monitoring website. One operator can monitor multiple pump sites simultaneously from anywhere in the world.

The components that make this type of pump station possible are the vacuum-priming pump and the air-water separator. The priming pump, usually a liquid-ring or rotary-vane vacuum pump, can be set up remotely several hundred feet away from the dewatering or bypass system and can be set at any elevation. The air-water separator, available in aluminum for ease of handling, is situated at the submersible pump for efficiency. This device allows the air and gases, not the water, to be drawn off the system by the vacuum pump, keeping the sub primed.

One of the nice features of this setup is that because the wet pump is already a submersible, if the area becomes flooded for any reason, the pump and dewatering or bypass system will not be damaged and can still function to help control the flooding, maintain the dewatered condition or maintain the bypass operation during the flood. Conversely, if the system runs dry, the oil bath in the sub will protect the seal until fluid flow returns.

Safety Measures
As with any pump system, the key to success is safety. Subs are usually electric-powered, although hydraulic-powered subs are a popular alternative. In either case, the operator must be cognizant of the dangers of working around electricity or high pressure.

When working with electric-powered subs in wet areas, particularly excavations or basements, it is a good idea to wear lineman’s gloves and rubber boots when handling the pumps. Workers should carry a meter to check for voltage before touching the pump to move it or work on it and use proper Lockout-Tagout procedures before disconnecting the power supply. Most importantly, never use the power cord as the tagline to pull or lift the pump: It is a power cord, not a rope.

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About the Author

Tom Minihan

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