The Trials and Tribulations of a Sump Pump

Many different pumps are used in common household applications. Pumps are used in water wells, dishwashers, washing machines, HVAC units, and sumps, to name a few. This article will concentrate on pumps used in domestic basement sumps. A sump is also known as a pit or a reservoir to typically collect high ground water or rain water. Many different types and manufactures of sump pumps are used across the nation. Submersible sump pumps are commonly constructed of cast iron and/or plastic, and as the name implies, they are completely submerged in water with the plug and electrical connection above the sump water level.

Submersible pumps have many advantages over the pedestal, or column, pump. Submersible pumps are smaller and have better motor cooling characteristics, which will extend the life of the pump. Submersible pumps also tend to be quieter due to the sound-dampening effects of the water.

Figure 1

Another common sump pump is the pedestal, or column, pump. This pump has the motor suspended above the sump in a dry environment. This type of pump has been in use for a long time; however, it is currently not as popular as the submersible sump pump. An advantage of the pedestal pump is that the motor is above the water level and is not immediately accessible to water infiltration. However, because of this, the pedestal motor housing is not water tight. In the event of a pump failure, the water level can rise and easily enter the motor housing.

Various orientations are possible with a sump. Two pumps may be used in conjunction to extend the life of the pump and to improve dependability. This configuration is called a “duplex system.” A battery operated backup pump can also be installed to increase the reliability of the system. Power outages often occur during inclement weather when sump pumps are needed the most, but with a battery backup pump in place a pump will continue to operate.

Battery backup systems can provide an additional level of confidence for any system. An alternative to the battery backup system is the water-powered type of system which does not use electricity to move an impeller to pump water, but instead will use domestic water pressure with a venturi and nozzle to move water. This type of system can be very useful during a power outage; however, the homeowner should be aware of the increased water usage and, consequently, the associated increased utility cost.

Many different accessories are available for the sump market. A check valve, which will only allow water to flow in one direction, is usually required on the pump discharge. A common type of check valve for the sump industry is a rubber flapper-type check valve. During normal operation the rubber flapper will swing open, allowing the water to discharge from the pump; however, when the pump stops operating, the flapper will swing closed, stopping any water remaining in the discharge line or above the pump from flowing back into the sump.

Manufacturers often require that a check valve be present in a sump pump installation. Various locations and distance requirements are listed and can be found in the installation instructions from the responsible manufacturer. Where the check valve is located can be very critical to an installation. The check valve will cause the discharge pipe to retain water, so this pipe needs to be properly installed to prevent freezing concerns. Also, when the flapper swings closed on a check valve, the resulting force of water will induce a water hammer effect on the discharge piping. A failure commonly associated with the check valve is a disconnected flapper lodging itself in the valve’s outlet, thus blocking the discharge flow of water.

A very common failure mode with sump pumps is that the pumps may become “air locked.” This condition would cause a perfectly operational pump to operate only intermittently. Pumps with bottom inlet designs can accumulate air within the pumping chamber, particularly when a check valve is installed on the discharge pipe. The impeller then spins within the air chamber and effectively pushes against the incoming water, prohibiting it from entering the pumping chamber. Many sump pumps have air release holes present in the pump housing, while many owner’s manuals instruct the installer to drill a hole or an additional hole in the discharge pipe to prevent this condition.

Figure 2

A properly installed sump will have a cover, which will prevent unwanted items from entering a sump. Common effluent pumps are rated to pass from 3/8-inch to 3/4-inch solids. However, debris present in a sump can cause various problems. A water loss may be the result of debris jamming the impeller. When a pump impeller is jammed with foreign debris, the pump motor stalls and is referred to be in a “locked rotor” condition. A pump in this condition will draw two to three times its rated electrical current. Pumps with thermal protectors will cycle on and off due to the associated heat and current. Once the thermal protector opens the electrical circuit and shuts the pump off, debris jamming the impeller can be released, with the pump operating normally thereafter.

A pump may also fail to operate due to the float switch being encumbered within the pit, prohibiting it from rising to the “on” position. The float switch being encumbered can be related to debris, improper tether length, damage, or improper sizing of the sump.

As with any electrical appliance, water and electricity do not mix. The pump seals are critical to the proper operation of a sump pump. Pump seals can be present around a switch arm, cap, motor housing, cord, test plug, or shaft seal. The shaft seal is a vital component that is designed to keep water out of the motor housing and to allow the motor shaft to rotate. Shaft seals can be made of various materials, including rubber, silicon carbide, carbon, and ceramic, to name a few. A pump switch has electrical contacts that open and close to activate a sump pump. Each time this occurs, a small arc is produced. The arcing and resulting heat will degrade the contacts.

Sump pumps are critical to keeping houses dry. They are a modern convenience that is becoming more prevalent with continued urban sprawl. Study of sump pump failures is crucial in order to identify the responsible parties, as well as to highlight improper installation techniques and to improve faulty designs.