What is a sanitary expansion vessel?

It is a component that absorbs the increased pressure of the hot sanitary water, maintaining the system's pressure stability.

How does a sanitary expansion vessel work?

It works by compressing an air cushion when the water in the tank expands due to heating.

What is the main function of the sanitary expansion vessel?

It reduces the pressure on the system and protects the sanitary water safety valve.

Where is the expansion vessel located in a boiler?

It is usually mounted near the storage tank or inside the boiler.

Does the expansion vessel need to be inflated?

Yes, it must be inflated to a specific pressure during regular maintenance.

How do you check the pressure of the expansion vessel?

By using a pressure gauge, you can check and adjust the pressure if necessary.

What are the signs of a faulty expansion vessel?

Water leaks, irregular water pressure, and frequent activation of the safety valve.

How do you replace an expansion vessel?

It should be replaced by a qualified technician to ensure proper installation.

How long does an expansion vessel last?

The typical lifespan is between 5 and 10 years, depending on use and maintenance.

What happens if the expansion vessel does not work properly?

It can cause excessive pressure in the system, leading to potential damage.

What is the difference between an expansion vessel and a water hammer arrestor?

The expansion vessel manages thermal expansion of water, while the water hammer arrestor cushions pressure spikes due to the opening and closing of faucets.

Why do modern boilers have smaller expansion vessels?

Due to reduced storage tank sizes and the use of more efficient technologies.

Is an expansion vessel necessary in an instantaneous boiler?

No, instantaneous boilers do not have storage tanks and therefore do not require an expansion vessel.

How do you maintain an expansion vessel?

By regularly checking the pressure and inflating it if necessary, along with periodic inspections by a technician.

What materials are used for sanitary expansion vessels?

Typically, metal for the outer structure and food-grade plastic for the internal diaphragm.

What does it mean if the sanitary water safety valve activates frequently?

It may indicate a problem with the expansion vessel, such as inadequate pressure or a damaged diaphragm.

How is an expansion vessel installed?

It must be installed by a professional following the manufacturer's specifications and local regulations.

What is the correct pressure for an expansion vessel?

It depends on the system but is generally between 0.5 and 1.5 bar.

Can an expansion vessel prevent noise in pipes?

Yes, it can help reduce noises caused by the thermal expansion of water.

When should an expansion vessel be replaced?

When it shows signs of failure, such as leaks or inability to maintain pressure.

What is the role of the expansion vessel in a closed system?

It keeps the system's pressure stable by absorbing the thermal expansion of water.

How do you inflate an expansion vessel?

Using a bicycle pump or compressor, add air through the Schrader valve.

Why is the expansion vessel important in a condensing boiler?

Because it helps manage water expansion when switching from heating to standby mode.

Does the expansion vessel require regular maintenance?

Yes, periodic checks of pressure and diaphragm condition are essential.

What causes the diaphragm in the expansion vessel to break?

Natural wear and tear, excessive pressure, or inadequate maintenance.

Sanitary Expansion Tank

The sanitary expansion vessel in storage boilers is essential when there is a significant storage capacity. As the water in the tank heats up, it expands in volume. This component reduces the load on the safety valve of the sanitary system.

It is not uncommon to find sanitary expansion vessels in boilers with storage tanks. These vessels are smaller and often made from food-grade plastics. When present, they must be properly inflated during regular maintenance.

Boilers with storage tanks are equipped with a sanitary expansion vessel, an air chamber component that performs a crucial function. If we go back 20 years, boilers with storage tanks had capacities up to 120 liters for wall-mounted units. In contrast, rapid boilers do not have a sanitary expansion vessel, and here’s why.

The sanitary expansion vessel consists of a metal container housing an air chamber. It mitigates the increase in pressure when the water in the storage tank heats up, compressing the air cushion to absorb the excess pressure.

This component hydraulically cushions the pressure of the sanitary water. As the water in the storage tank heats from 20 to 45 degrees Celsius, the water expands since it is incompressible, putting stress on the safety valve. Therefore, the sanitary expansion vessel is unnecessary in rapid boilers because there is no storage.

Nowadays, boilers have different storage capacities compared to the past. Keeping a 60-liter tank warm results in higher gas consumption. A typical family of 3-4 people can now suffice with a 20-liter storage boiler. Thus, the expansion vessel may shrink from 2 liters to something akin to a water hammer arrestor or disappear entirely. Many budget models do not include one at all.

Given that the expansion vessel performs its function when there is a noticeable temperature difference, its role is rare but crucial. Daily use of hot water releases excess pressure as the boiler maintains a constant temperature. However, if the boiler is turned off and then back on, the storage tank will have a temperature difference, and this is when the expansion vessel is needed.

As mentioned earlier, a water hammer arrestor serves a similar function to the expansion vessel. In systems where the water mains have higher pressures or where there is an autoclave, this component is indispensable. Opening and closing a tap creates a pressure difference that can result in noise. The water hammer is thus cushioned by this component, which I will discuss in another article.

Essential Habits

When going on vacation, you might consider turning off the boiler. This is not a bad idea in the summer, but upon returning, follow this procedure.

As the water in the storage tank cools, the problem of leaks may arise upon return. To relieve excess pressure while the boiler is heating the sanitary water, open a hot water tap for 5 seconds after 2-3 minutes of turning the boiler back on.

This procedure ensures that excess pressure does not compromise the sanitary water safety valve. It needs to be done only once when restarting the appliance; once at temperature, it is no longer necessary.