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Home > Tank Applications > HVAC Expansion Tanks

HVAC Expansion Tanks

Expansion tanks are required in a closed loop heating or chilled water HVAC system to absorb the expanding fluid and limit the pressure within a heating or cooling system. A properly sized expansion, or compression tank, will accommodate the expansion of the system fluid during the heating or cooling cycle without allowing the system to exceed the critical pressure limits of the system. The expansion tank uses compressed air to maintain system pressures by accepting and expelling the changing volume of water as it heats and cools. Some tank designs incorporate a diaphragm or bladder to isolate the expanded water from the pressure controlling air cushion. As water is expanded, it is contained in the bladder preventing tank corrosion and water logging potentials. The pressure controlling air cushion is pre-charged at the factory and can be adjusted in the field to meet critical system requirements. This design and operation of this style of expansion tank allows the designer/specifying engineer to reduce tank sizes up to 80%.

HVAC Expansion Tank Styles

Compression Tanks

This tank is the oldest style that has been used in systems for many years. It works well when the air is controlled and kept in the tank, not in the system.

NA Series (ASME)
Stainless Steel NA Series (ASME)

Bladder Tanks

A bladder tank is a tank that has a membrane between the air and water. This allows the tank to be pre-charged with air to the minimum operating pressure and thereby reduces the tank size and the installed weight. Bladder tanks are often referred to as replaceable diaphragm tanks.

NLA Series (ASME)
NLAP Series (ASME)
NL Series (Non-ASME)

Diaphragm Tanks

A diaphragm tank is designed in such a way that the diaphragm cannot be replaced if the tank fails. The advantage of this style is the initial cost. On smaller tanks the cost of replacing a bladder may exceed the cost of replacing the tank. Diaphragm tanks are often referred to as fixed diaphragm tanks.