Although the water in your water heater doesn’t reach the boiling point and turn into steam, it does expand when heated up. This is called thermal expansion.
This extra pressure will just get absorbed by the municipality’s water supply system and become negligible. No problem. However, if a check valve or a pressure regulating valve (PRV) is installed on the water supply line coming into your home, it keeps all that excess pressure trapped in your home’s plumbing system which stresses your supply lines, fixtures, and appliances.
That’s where the expansion/ pressure vessel comes in. Properly installed, it absorbs this excess pressure. Half of the tank is filled with water from the main water system of your home. The other half is filled with compressed air. There is a butyl rubber bladder in the middle. As the water in your water heater gets hotter and expands, it pushes against that bladder and further compresses the air on the other side.
When is it required?
An expansion tank is always highly recommended if you have a ‘closed-loop system’ caused by any kind of check valve or pressure regulating valve installed on your house’s water supply line.
A common illustration compares having high water pressure in your home to having high blood pressure. It usually doesn’t have immediate negative consequences. However, the long-term wear and tear of this excess pressure can reduce the life expectancy of everything in your plumbing system. The weakest parts of the system are usually the toilet fill valves, the supply lines, and the solenoid valves found in washing machines, dishwashers, and ice makers. These are much more likely to fail prematurely when exposed to high water pressure.
If you have excess pressure over 80 P.S.I. supplied to your home by the city water supply, an expansion tank by itself does nothing to correct this. That’s the job of the pressure reducing valve (PRV). When the pressure supplied to your home is at the proper level between 40 and 80 P.S.I. and you have a PRV or check valve, that’s where the thermal expansion tank comes in. It protects against the constant fluctuation of high pressure caused by thermal expansion upon a closed-loop system.
Depending on where you live, an expansion tank might be required by the city regardless of the water pressure in order to pass plumbing inspections – such as you would get upon the installation of a new water heater.
For more info contact wates pressure vessel supplier in uae or call us at +971 4 252 2966