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.
