Expansion Water Tanks

There are two common types of expansion water tanks that are used on hot water boiler systems; the steel and the bladder expansion tank. Both of these are used to provide enough of a cushion so that the water is able to expand when heating without causing any problems.

If there was no cushion of air the pressure inside would rise and eventually exceed the setting on the relief valve. When this happens the relief valve will open and discharge water so that the pressure is relieved. If you have this problem than you know the first thing to look at is the expansion tank.

Steel Expansion Tanks

The steel tanks are not the most popular – but they are still used in some of the older systems. In this unit the air and the water will touch each other and the air will compress when the water is being heated. The air is than compressed inside of the loop system to create the cushion. It will absorb the excess pressure.

Bladder Expansion Tank

In this tank the air and the water are separated through the use of a diaphragm. This tank is used in the newer systems including the ones equipped with a hydronic loop. The loop helps to control the pressure and must stay at the right level in order to work properly. It helps to install this before the suction side of the circulator pump that is in the supply side of the unit.

Because the bladder expansion tank will absorb the excess pressure inside of the hydronic loop it would help to add the make up water for the unit and hydronic loop close to where the tank is. This will help to keep the pressure relief valve, hydronic loop, and expansion tank at the right settings and with no excess pressure build up.