What Is an Expansion Tank?

An expansion tank is a component used in mechanical systems to balance pressure.

When the water inside the system heats up, its volume expands. If this expansion is not controlled:

• pressure rises
• the system can be damaged
• equipment can malfunction

The expansion tank absorbs this excess volume and balances the system pressure.

Expansion tanks are used especially in the following systems:

• booster pump systems
• central heating systems
• boiler rooms
• underfloor heating systems
• solar energy systems

What Is a Steel Expansion Tank?

A steel expansion tank is a tank that contains no membrane and consists entirely of a steel body.

In these tanks, water and air occupy the same space.

When the water in the system expands, the air inside the tank is compressed and balances the pressure.

Advantages

• can be used in large systems
• tanks with high volume can be produced
• long service life

Disadvantages

• air can mix into the water over time
• air can form in the system
• requires maintenance

For this reason, steel expansion tanks are generally used in large boiler rooms.

What Is a Membrane Expansion Tank?

In membrane expansion tanks, water and air are separated from each other by a rubber membrane.

The tank contains two sections:

• water section
• air section

Thanks to the membrane, water and air do not mix.

Advantages

• requires no maintenance
• no air forms in the system
• provides more stable pressure
• ideal for booster pump systems

Disadvantages

• the membrane can wear out over time
• can be expensive in very large capacities

Which Tank Is Used in Booster Pump Systems?

In booster pump systems, membrane expansion tanks are generally used.

Because these tanks:

• keep the pressure more stable
• prevent the pump from switching on too frequently
• require no maintenance

For this reason, the membrane tank is preferred in residential and apartment booster pump systems.

Which Tank Is Used in Central Heating Systems?

Both tank types can be used in central heating systems.

However, in modern systems, generally:

the membrane expansion tank

is used.

How Is Expansion Tank Capacity Selected?

The following parameters should be considered when selecting an expansion tank:

• system water volume
• working pressure
• maximum temperature
• safety margin

An incorrect tank choice can cause pressure problems in the system.

Expansion Tank Brands

There are many quality expansion tank manufacturers on the market.

The brands frequently preferred at POMEKA are as follows:

• Varem expansion tanks
• Reflex expansion tanks
• Zilmet expansion tanks
• Cimm expansion tanks
• Aquasystem tanks

These brands offer reliable solutions for booster pump and heating systems.

Why Does an Expansion Tank Fail?

Some problems can occur in expansion tanks over time.

The most common problems are:

• membrane rupture
• drop in air pressure
• corrosion inside the tank

These problems can cause the booster pump system to switch on continuously.

How Many Bar Should the Air Pressure Be in a Membrane Tank?

In membrane tanks, the air pressure is generally set within the following range:

1.5 – 2 bar

This value should be adjusted according to the system pressure.

Which Is Better: Steel Tank or Membrane Tank?

In residential and booster pump systems, membrane expansion tanks are generally more advantageous.

Because:

• requires no maintenance
• no air forms in the system
• provides more stable pressure

However, steel expansion tanks can be used in very large boiler rooms.

Conclusion

Choosing the right expansion tank is very important for the efficient operation of the system.

In general:

• residential and booster pump systems → membrane tank
• large boiler systems → steel tank

are preferred.

A correctly selected expansion tank prevents pressure problems in the system and extends the equipment's service life.