What Is an Expansion Tank?
An expansion tank is a small vessel connected to a water heater that absorbs pressure from heated water. Its internal air cushion gives the water room to expand. This helps limit pressure changes in a closed plumbing system and can reduce stress on pipes, fittings, valves, and the water heater.
Quick Facts About Expansion Tank
Category
Water heater accessory
Used for
Managing thermal expansion
Common confusion
Not a water storage tank
Also called
Thermal Expansion Tank
Often discussed with
Water Heater Installation
Key Takeaways About Expansion Tank
- It contains an air cushion beside the water heater.
- It helps control pressure in closed plumbing systems.
- It isn't a backup water heater or storage tank.
How Expansion Tank Works
Expansion tank operation depends on an air cushion inside the tank. As water heats, the water expands and pushes against a flexible diaphragm or bladder. The air space compresses and accepts part of that pressure.
Related glossary terms: Pressure Reducing Valve, Water Hammer, Thermostatic Mixing Valve.
A plumber connects the tank to the cold water line near the water heater. The tank's air pressure must suit the plumbing system and the water heater setup. A pressure gauge helps check the system, while a visual inspection can reveal corrosion, leaks, or poor support.
Water heater service may include checking the connection, mounting, and nearby shutoff valve. A properly supported tank should not pull on the pipe. The tank also needs room for inspection and future replacement.
Expert Note
When we install a water heater, we check whether an expansion tank fits the system design. We inspect the connection, support, and air pressure. Our team also looks for leaks or corrosion around the tank and nearby fittings.
Expansion Tank in Practice: A Real-World Example
A Kent homeowner replaces a water heater in a home with a closed plumbing system. The installation includes an expansion tank on the cold water line, with secure support and a checked connection.
Related Services
Related Terms
Pressure Reducing Valve
A Pressure Reducing Valve is a plumbing control that lowers high incoming water pressure to a…
Water Hammer
Water Hammer is a pressure surge that occurs when moving water stops or changes direction quickly…
Thermostatic Mixing Valve
A Thermostatic Mixing Valve is a temperature-control device that blends hot and cold water before water…
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