AHG Solutions Guide_Edition 2.7

Contents
Dirt and Air Separation
Air
Due to the physical nature of water, it is impossible to
prevent air from becoming trapped in the system.
Air can enter through:
• Filling and makeup water
• System alterations and maintenance
• Open header tanks
• Micro leaks and diffusion through system components
• Henry’s Law - “Gas is a natural constituent of water and
other liquids. The presence and solubility depend on
temperature and pressure within the liquid” (William Henry
(1775 – 1836)
Free Air
Microbubbles
Dissolved Air
Once in the system, gas can be observed in
three different forms
As Henry’s Law describes, the presence and solubility of
gas in a liquid depends on two elements – temperature and
pressure. Whereas a hot water system causes the water to
expand and the gas more easily removed, a chilled water
system results in the water becoming dense and the gas
more soluble.
Similarly, where the system pressure is low, degassing is
more easily achieved. But as the pressure increases, not
only is the presence of gas greater but it also becomes
much more difficult for traditional methods of removal –
such as air vents – to release it.
Free Air
“Free” gas or air is both the most common and most easily
removed, as it has not yet become soluble in the water. It
can be found as air pockets and is typically released via
simple air vents strategically placed around the system.
A Duraflex EcoTop Automatic Air Vent removes free air
quickly, offering continuous, maintenance-free operation
and high reliability.
Microbubbles
Where gas has entered the liquid at some pressure,
microbubbles are often formed. Smaller than one
millimeter in diameter but larger than one micrometer,
these bubbles of gas are created by turbulence in the water
(often where there is a loss of pressure, such as a pumping
pillar) and are commonly in hot water systems.
Although visible to the eye, microbubbles cannot be
removed by air vents as they are carried with the water
stream. Rather, an air separator like a Duraflex EcoVent,
which is suitable for heating systems up to 300 kpa, should
be installed on the flow side of the heat source for effective
deaeration.
By slowing the water down as it passes through the mesh
in the chamber, the microbubbles are broken up and the
gas separates out of the water stream and is vented at the
top of the chamber.
Dissolved Air
But where the pressure is higher and/or the temperature is
low – as is common in chilled water systems – most gases
become totally solubilised in the water.
In much the same way carbon dioxide remains invisible in
a bottle of lemonade until opened, the solubilised gas can
only be removed from the water stream by reducing the
pressure.
A Duraflex Vacuum Deaerator removes dissolved air
quickly, offering continuous operation and high reliability.
EXPANSION &
DEAERATION
191