Domestic Water Expansion Tank Specifications

Watts PLT-5 Potable Water Expansion Tank (0067370)

• 3/4" male connection,
• Tank volume 2.1 gallon.

Domestic Potable Water Expansion Tank

 Domestic Potable Water Expansion Tanks manufactured by Watts

 Watts - Domestic Potable Water Expansion Tanks are used on gas, oil, or electric, direct-fired, residential water heater and hot water storage tank applications to absorb the increased volume of domestic water created by thermal expansion. Watts - Domestic Potable Water Expansion Tanks also maintains balanced pressure throughout the domestic water supply system by keeping system pressure below the T&P relief valve setting. It is a pre-pressurized, field-adjustable steel tank with an FDA-approved Butyl rubber diaphragm, and brass 3/4 in. inlet connection. An expansion membrane prevents air-to-water contact in the tank ensuring a long system life. IAMPO listed and ANSI/NSF 61 certified. The Watts, Potable Water Expansion Tank mounts in-line on the piping system.

What is thermal expansion?

When water is heated, it expands. For example, water heated from 90 degrees F to a thermostat setting of 140 degrees F in a 40 gallon hot water heater will expand by almost one-half gallon. This is because when water is heated, its density decreases and its volume expands (see below). Since water is not compressible, the extra volume created by expansion must go someplace. During no-flow periods in a system, pressure reducing valves, backflow preventers, and other one-way valves are closed, thus eliminating a path for expanded water to flow back to the system supply. Hence, system pressure increases.

Temperature vs. Density

Thermal expansion of water in a closed plumbing system can create a number of annoying and potentially dangerous problems. These include: the build up of unusually high pressure in a system (even when a pressure reducing valve is installed); pressure surges; and the chronic or continuous dripping of a temperature and pressure (T&P) relief valve. In addition, dripping faucets and leaking toilet tank ball cock fill valves are also symptomatic of thermal expansion.

More serious problems can also occur due to thermal expansion. When dangerous pressures are built up in a water heater, internal parts may fail such as the internal flues, fittings or water connections. If a flue way collapses it can lead to the potential release of toxic gases, such as carbon monoxide into living spaces. Thermal expansion can also lead to a ruptured or distorted hot water heating tank and may void the manufacturer's warranty.

Plumbing codes require you to address this safety problem. No matter what your thermal expansion problem may be, whether for new construction or for retrofitting or remodeling an existing system, Watts offers cost effective solutions for you as outlined in the following pages of this guide. Should you require more detailed information on these products, please feel free to call us.

Expansion Tanks

How a Diaphragm Expansion Tank Works

When water is heated in a closed system it expands. Water is not compressible, therefore, the additional water volume created has to go someplace. When an expansion tank is installed the excess water enters the pre-pressurized tank (figure 1). As the temperature and pressure reaches its maximum, the diaphragm flexes against an air cushion (air is compressible) to allow for increased water expansion (figure 2). When the system is opened again or the water cools, the water leaves the tank and returns to the system.

Hot Water Expansion Tanks Potable vs. Non-Potable

Potable vs Non-Potable Hot Water Systems - Regarding Expansion tanks

Potable refers to water in an open domestic hot water heating system. This is water that could potentially be consumed by people and is not recirculated within the system. Non-potable refers to water in a closed hydronic heating, radiant floor heating, or a chilled water system where the water is recirculated and does not leave the system. Each of these hot water heating systems have different thermal expansion requirements explained in more depth in the specification sheets accompanying each thermal expansion solution.

Plumbing codes require that thermal expansion control be addressed in plumbing systems. A temperature and pressure relief valve is not considered a thermal expansion device. This is because when water is allowed to continuously drip from the T&P relief valve, minerals from the water can build up on the valve, eventually blocking it. This blockage can render the T&P valve useless and potentially lead to hot water heater explosions. The International Plumbing Code (IPC), Uniform Plumbing Code (UPC) and Standard Plumbing Code all require thermal expansion control to be addressed.

Section VIII of the ASME Boiler and Pressure Vessel Code states certain requirements that must be met by an expansion tank for it to meet ASME construction specifications. The Watts Series ETA, ET-RA and DETA tanks all meet these ASME requirements.

Water Containment solutions allow for thermal expansion while containing thermally expanded water in the plumbing system. The Watts full line of thermal expansion tanks are considered water containment devices. These products require no installation of discharge lines or drains.

Water Relief solutions discharge thermally expanded water at a pressure setting that is below the setting of the water heater's temperature and pressure relief valve. Watts offers a variety of water relief solutions that can be installed on the system piping, in a water closet or on an outside faucet. These products must be piped to a suitable drain or discharge location.

Potable Systems

Control Thermal Expansion in Hot Water Supply Systems. Thermal expansion of heated water may occur wherever potable water is heated in a closed system (when the potable water is isolated from the public water supply by a one-way valve, such as a pressure reducing valve, backflow preventer or check valve).

Watts potable water expansion tanks are designed to absorb the increased volume of water created by thermal expansion and to maintain a balanced pressure throughout the potable water supply system. They are used to prevent plumbing system and/or water heater damage and unnecessary relief valve discharge caused by excessive pressure from thermal expansion.