Expansion tank
Encyclopedia
An expansion tank or expansion vessel is a small tank
used to protect closed water heating
systems and domestic hot water systems from excessive pressure. The tank is partially filled with air, whose compressibility cushions shock caused by water hammer
and absorbs excess water pressure caused by thermal expansion
.
The modern vessel is a small container divided in two by a rubber diaphragm. One side is connected to the pipe work of the heating system and therefore contains water. The other, the dry side, contains air under pressure, and normally a Schrader valve
(car-tire type valve stem) for checking pressures and adding air. When the heating system is empty or at the low end of the normal range of working pressure the diaphragm will be pushed against the water inlet. As the water pressure increases, so the diaphragm moves compressing the air on its other side. An older style of expansion tank is larger, oriented horizontally, and has no rubber diaphragm.
When expansion tanks are used in domestic hot water systems, the tank and the diaphragm must conform to drinking water
regulations and must be capable of accommodating the required volume of water.
In the past, domestic plumbing systems often contained more air than they do currently. Thus, expansion tanks are now used more frequently than in the past.
In the UK, prior to the use of sealed expansion tanks, 'open' tanks were installed in the roof space to accommodate the water's expansion; these had the disadvantage of being exposed to the cold air in the roof space. This, without effective loft insulation, could fall below freezing, and could cause the pipework supplying the tank to freeze. However with good pipe and tank insulation, this was in practice quite rare. Although such systems were remarkably trouble free, there are concerns about the potability of water from roof tanks due to the possibility of contamination. The other major disadvantage is that the water pressure from a roof tank is considerably lower than mains water pressure, making the use of mixer taps sometimes unpredictable.
In Europe the design and the construction of expansion tanks are ruled by EN 13831 according to Pressure Equipment Directive (PED) 97/23/EC
An expansion tank is also used in the cooling system of most internal combustion engine
s, to allow the antifreeze
and air in the system to expand with rising temperature and pressure.
Water tank
A Water tank is a container for storing water. The need for a water tank is as old as civilized man, providing storage of water for drinking water, irrigation agriculture, fire suppression, agricultural farming, both for plants and livestock, chemical manufacturing, food preparation as well as many...
used to protect closed water heating
Water heating
Water heating is a thermodynamic process using an energy source to heat water above its initial temperature. Typical domestic uses of hot water are for cooking, cleaning, bathing, and space heating...
systems and domestic hot water systems from excessive pressure. The tank is partially filled with air, whose compressibility cushions shock caused by water hammer
Water hammer
Water hammer is a pressure surge or wave resulting when a fluid in motion is forced to stop or change direction suddenly . Water hammer commonly occurs when a valve is closed suddenly at an end of a pipeline system, and a pressure wave propagates in the pipe...
and absorbs excess water pressure caused by thermal expansion
Thermal expansion
Thermal expansion is the tendency of matter to change in volume in response to a change in temperature.When a substance is heated, its particles begin moving more and thus usually maintain a greater average separation. Materials which contract with increasing temperature are rare; this effect is...
.
The modern vessel is a small container divided in two by a rubber diaphragm. One side is connected to the pipe work of the heating system and therefore contains water. The other, the dry side, contains air under pressure, and normally a Schrader valve
Schrader valve
The Schrader valve is a brand of pneumatic tire valve used on virtually every motor vehicle in the world today. The Schrader company, for which it was named, was founded in 1844 by August Schrader...
(car-tire type valve stem) for checking pressures and adding air. When the heating system is empty or at the low end of the normal range of working pressure the diaphragm will be pushed against the water inlet. As the water pressure increases, so the diaphragm moves compressing the air on its other side. An older style of expansion tank is larger, oriented horizontally, and has no rubber diaphragm.
When expansion tanks are used in domestic hot water systems, the tank and the diaphragm must conform to drinking water
Drinking water
Drinking water or potable water is water pure enough to be consumed or used with low risk of immediate or long term harm. In most developed countries, the water supplied to households, commerce and industry is all of drinking water standard, even though only a very small proportion is actually...
regulations and must be capable of accommodating the required volume of water.
In the past, domestic plumbing systems often contained more air than they do currently. Thus, expansion tanks are now used more frequently than in the past.
In the UK, prior to the use of sealed expansion tanks, 'open' tanks were installed in the roof space to accommodate the water's expansion; these had the disadvantage of being exposed to the cold air in the roof space. This, without effective loft insulation, could fall below freezing, and could cause the pipework supplying the tank to freeze. However with good pipe and tank insulation, this was in practice quite rare. Although such systems were remarkably trouble free, there are concerns about the potability of water from roof tanks due to the possibility of contamination. The other major disadvantage is that the water pressure from a roof tank is considerably lower than mains water pressure, making the use of mixer taps sometimes unpredictable.
In Europe the design and the construction of expansion tanks are ruled by EN 13831 according to Pressure Equipment Directive (PED) 97/23/EC
Internal combustion engine
The internal combustion engine is an engine in which the combustion of a fuel occurs with an oxidizer in a combustion chamber. In an internal combustion engine, the expansion of the high-temperature and high -pressure gases produced by combustion apply direct force to some component of the engine...
s, to allow the antifreeze
Antifreeze
Antifreeze is a freeze preventive used in internal combustion engines and other heat transfer applications, such as HVAC chillers and solar water heaters....
and air in the system to expand with rising temperature and pressure.