Working Principle of Expansion Tanks
In the selection of expansion tanks, tank volume and pressure criteria should be taken into consideration. Another name for expansion tanks, also known as hydro-pneumatic tanks, their basic operating principle is based on these two criteria.
Expansion tanks are now a standard part of both heating systems and hydro-pneumatic installations, so it is possible to see at least one expansion tank in every boiler room. Hydro-pneumatic tanks are used in small capacity devices such as combi boilers and floor-standing boilers, integrated directly into the product. There is no difference in the operating principles between Expansion Tanks used in these small capacity devices and those used in large capacity systems, both of which are indispensable parts of systems that operate smoothly and stably. Expansion tanks, whether large or small, are used to absorb the pressure created by the expanding fluid in the system.
There are two types of expansion tanks: open and closed.
Diaphragm-type Closed Expansion Tank
In diaphragm-type tanks, water comes into contact with the metal. Diaphragm-type tanks can only be used in closed-loop heating systems. This is because only fresh water is taken into the system during the initial startup. Later, this water remains in the system continuously. The oxygen in the water causes minimal rusting in the radiators, boiler, and tank walls. However, once the oxygen is depleted, rusting ceases. If a diaphragm-type expansion tank is attached to a hydro-pneumatic system, rapid rusting occurs because fresh water constantly enters the tank, leading to tank rupture.
Bladder-type Closed Expansion Tank
In bladder-type membranes, water does not come into contact with the metal. It is always inside the membrane. Therefore, bladder-type membranes can be used in both heating systems and hydro-pneumatic installations. Small-capacity bladder-type expansion tanks are without suspension. However, in larger types, the membrane is suspended from above.
Expansion Tanks in Natural Gas and Liquid Fuel Heating Systems
Expansion tanks are used in closed-loop natural gas or liquid fuel heating systems in addition to hot water systems. This is because fuel feed in these systems is fully controlled, and the entire system operates on electricity. If there is a power outage, everything stops, and the boiler starts to cool immediately. In other words, there is no risk of uncontrolled temperature increase. Ideally, nitrogen gas is preferred to be pressurized into the expansion tanks. Nitrogen diffuses into water from the membrane more slowly than oxygen. Therefore, it can remain in the tank for a longer period. Additionally, since nitrogen is non-corrosive like oxygen, even if it mixes with water, it does not cause corrosion in the system. However, due to the difficulty of finding compressed air, let alone nitrogen, in construction sites or buildings, and because 75-78% of air is nitrogen, air is generally used instead.