Ultra-high pressure (UHP) air is a specialised form of compressed air
typically used in marine and military applications. Instead of being compressed
to the standard 7 barg, UHP air is often supplied at 450 barg, which means dry
air without any water vapour is a critical consideration, both for energy savings
and for safety. Given the high pressures, even a small amount of water vapour
would condense at ambient temperatures.
Air supplied at high pressure is a good source of power, making it ideal
for applications such as clearing submarine ballast tanks for ascent to the
surface. The high pressure of the air allows the tanks to be cleared quickly,
and gives the crew a greater level of control and responsiveness.
However, the cold temperatures below sea, as well as the cooling effect
of reducing the pressure of a gas could lead to moisture in the UHP air. If ice
is formed, it could block or damage the equipment and completely disable the
One of Michell’s longstanding customers, S.A. Marine Pty. Ltd from
Australia specialises in evaluating and testing UHP air systems. Due to the
high pressures involved, it’s vitally important that the air is pure and free
from contaminants such as compressor oil particulates or water.
S.A. Marine’s portable test set consists of a desiccant dryer to remove
vapour from the air and an on-line hygrometer from Michell to measure the water
dew point at delivery. Michell’s ceramic impedance sensor is able to measure
the dew point temperature at line pressure, giving S.A. Marine complete
confidence in their measurements.
The company also provides an inspection service for breathing air
cylinder-filling apparatus for both naval and commercial customers. Even in
this application, too much moisture could lead to potential bacterial growth
and pose health problems for users. S.A. Marine uses a Michell chilled mirror
hygrometer as a high-precision calibration reference on a test rig at their
S.A. Marine managing director Greg Fahill comments that Michell offers
the only hygrometers that are reliable at UHP conditions.