By Tom McDermott and Dave Greisinger
Summary: Over 1.5 billion people use water wells as their primary source of drinking water. In the United States, 10 million private water wells supply drinking, washing, bathing and irrigation water needs for 23 million people. This article focuses on the electrically powered jet and submersible centrifugal pumps, and water systems that normally deliver this water in the developed world.
During the 1940s in the United States, electricity generally became available in rural areas due to the expansion of rural electrification under the federal Rural Electrification Administration (REA). As a result, the tiresome job of hand pumping and hauling water from domestic water wells was, in many areas, replaced with motor-driven pumps. Generally speaking, the motor-driven water pumps most in use today are centrifugal pumps and can be classified as either jet pumps or submersible well pumps. Jet pumps are aboveground and can be further broken down into shallow well and deep well jet pumps. Submersible pumps, as their name implies, are submerged in the well water.
Shallow & deep well jet pumps
A shallow well jet pump, limited by atmospheric pressure, can lift water about 25 feet. Deep well jets are most effective to about 100 feet. Jet pumps essentially operate on the principal of filling a vacuum. (Imagine sucking on a straw and removing the air and, as this is done, the liquid rises to fill the vacuum that’s been created.) Since jet pumps don’t pump or evacuate air, they use water in the system to move water from the well to the pump and into the household water system.
Jet pumps draw water from a well by creating a vacuum through the combined efforts of the impeller and diffuser as well as the jet ejector, which is made up of a nozzle and venturi (see Figure 1). As the impeller moves water out of the pump housing, it pulls water from the well. This water passes through a nozzle, which constricts the flow of the water through its progressively narrower opening, thereby increasing the speed (velocity) of the water and creating a partial vacuum at the end of the nozzle. In many pump manuals, this is compared to the nozzle on a garden hose. Once the water passes through the nozzle, it moves into a larger-diameter venturi that slows down the water and increases the pressure in the pump. The water then enters the pump housing where the impeller moves a portion of the water into the household water system while some of the water is recirculated by the impeller and used to draw more water out of the well. This recirculated water is referred to as “drive water.”
Spotting the ejector
The fundamental difference between a shallow well jet pump and a deep well jet pump is the location of the jet ejector. A shallow well jet pump has the jet ejector attached to the pump housing and is aboveground like the pump. A deep well jet pump has the jet ejector assembly down in the well, either submerged or close to the pumping level of the water.
A typical deep well jet pump installation uses a two-pipe system. One pipe is called the pressure or drive pipe that sends drive water from the surface pump (see Figure 1) to the jet ejector nozzle, creating a partial vacuum that fills with well water. This drive water along with well water flows up the second pipe (suction pipe) to the pump on the surface. Another type of deep well jet installation is called a “packer style” and uses the well’s casing, usually 2-inch, as the pressure pipe feeding the packer jet assembly—fitted tightly into the well casing—with drive water. The well water and drive water then flow to the surface pump through the suction pipe, as in the two-pipe installation (see Figure 2).
The installation of the jet ejector down in the well allows the deep well jet pump to overcome the restrictions of an aboveground jet ejector and the 25-foot suction limit. Both shallow well and deep well jets use foot valves or check valves in drilled-well applications. In driven wells using well points, a shallow well installation uses a check valve near the jet ejector while deep well installations use a foot valve at the bottom of the suction pipe to keep the pipe full of water between pump cycles (see Figure 2).
The depth from which the water is drawn and the ability to build significant pressure limit the performance of jet pumps. For example, a typical ½ horsepower (hp) shallow well jet pump will only produce about 8 gallons per minute (gpm) at a 15-foot suction lift at 40 pounds per square inch (psi). Likewise, a typical ½ hp deep well jet pump will only pump 5.5 gpm from a 60-foot water level. Nevertheless, jet pumps remain popular as over 400,000 are sold annually in the United States (see Table 1).
Submersible water well pumps
Simply put, submersible water well pumps “push” the water out of the well rather than “pull” the water out like jet pumps. Submersible well pumps are complete units with a pump end made up of a series of matching impellers and diffusers called stages, and an attached motor to turn the impellers and diffusers in the pump end. The submersible pump is submerged in the water down in the well and drives the water up the discharge piping to the pressure tank.
Submersible pump performance is a function of capacity and pressure. A submersible pump is designed to deliver certain flows at given pressures from specific pumping levels. The design of the impellers and diffuser determine the capacity and pressure of a submersible pump end. Capacity is, for the most part, based on the width of the impeller and diffuser. The pressure is dependent on the diameter of the impeller, the number of impellers, and the speed at which the impellers rotate. Most U.S. residential submersible pumps are 4-inch pumps coupled with constant speed, 4-inch motors operating at 3,450 revolutions per minute (rpm).
Pump manufacturers normally design their pumps to fall into ranges such as 10-25 gpm. Within these gpm ranges, a number of motor choices will be offered based on the proper combination of capacity to pumping level to horsepower. It’s important to remember that horsepower by itself isn’t the arbiter of submersible pump performance. Selection of a pump based solely on horsepower is a common error.
Residential submersible pump motors are manufactured in either a 2-wire or 3-wire configuration. A 2-wire pump motor doesn’t have a control box with a motor start capacitor, but rather includes the start capacitor in the submerged pump motor. A 2-wire pump motor is wired directly to the pressure switch and 3-wire submersible pump motors are wired from the well to a wall-mounted control box with relay and start capacitor and then to the pressure switch.
Weighing the pros and cons
The clearest benefit of the submersible pump over the jet pump is the ability to deliver higher capacities from deeper levels at significant pressures to the household water system. Of course, a negative is that a submersible pump must be pulled from the well to be serviced; not so with a jet pump, unless it’s a deep well installation with a faulty jet ejector (see Figure 3).
Nationally, submersible water well pumps have become more popular than jet pumps in residential well installations; however, there are areas where jet pumps clearly outstrip submersible pump installations. Generally, jet pumps are more common in warmer climates (see Table 1) and areas with higher water tables .
This is an exciting time in the private water system and water well pump industry. As larger homes are being built on private wells, with correspondingly larger water supply needs, the challenges of sizing an adequate private water supply system have never been greater. Combine the increased demands on water supply with consumer concerns over water quality and water disposal, and the stage is set for new technologies to respond to new expectations.
It’s fair to say that today’s consumer doesn’t want to have their dream home where there’s not a municipal water supply or have their private water supply limited. The expectation is to build a home the customer wants. The challenge for the private water system installer is to make sure that the right pump and water system have been installed to produce the water needs—supply and pressure—that the water treatment equipment, plumbing fixtures and lifestyle of the consumer demand.
The authors would like to thank Franklin Electric, of Bluffton, Ind., which manufactures more than 90 percent of submersible pump motors used in the United States. Understanding this motor and its characteristics is key to maintaining submersible pump performance and troubleshooting.
- Ground Water’s Role in America’s Economic Vitality, National Ground Water Association, 601 Dempsey Road, Westerville, OH 43081, 2001, www.ngwa.org
- Water Systems Handbook—11th Edition, Water Systems Council, 1101 30th Street, N.W., Suite 500, Washington, DC 20007, 2000, www.watersytemscouncil.org
- Klenck, Thomas, “Water-Well Pump,” Popular Mechanics, http://popular mechan-ics.com/home_improvement/how_it_ works/, 1997.
- Pump Basics, How A Centrifugal Pump Works, A.Y. McDonald Manufacturing, http://www.aymcdonald.com/GenInfo/Pumps/PumpBasics.pdf, 2000.
About the authors
Tom McDermott, Jr. is president of A. I. McDermott Co. Inc., Oshkosh, Wis., a multi-branch distributor of water well, wastewater and water treatment supplies, pumps, plumbing and hydronic heating equipment in Wisconsin and Upper Michigan. He is the third generation of his family to be involved in the private water system business in Wisconsin.
Both can be reached at (920) 231-7080, (920) 231-6041 (fax) or website: www.aimcdermott.com