Ultra-high pressure (UHP) air is a specialised form of compressed air. Rather than being compressed to the standard 7 barg, UHP air is often supplied at 450 barg.
Drying the air is a critical consideration – both for energy-saving and for safety. Given the high pressures, even a small amount of water vapour would condense at ambient temperatures.
Supplying air at high pressure makes it a good source of power. Because of the extra force it provides, it's often used in marine and military 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.
Due to the cold temperatures below sea, as well as the cooling effect of reducing the pressure of a gas, it is vitally important to avoid excess moisture in the UHP air. If ice formed it could block or damage the equipment and completely disable the submarine.
One of Michell's long-standing customers, S.A. Marine Pty. Ltd from Australia specialise 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 uses a desiccant dryer to remove vapour from the air and use an on-line hygrometer from Michell to measure the water dew point at delivery, as part of their portable test set. The Michell ceramic impedance sensor is able to measure the dew-point temperature at line pressure which gives S.A. Marine complete confidence in their measurements.
They also provide an inspection service for breathing air cylinder-filling apparatus for both naval and commercial customers. In this case, too much moisture would lead to the potential bacteria to grow and pose health problems for the users. Back at their company facilities, S.A. Marine use a Michell chilled mirror hygrometer as a high-precision calibration reference on a test rig.
Greg Fahill, the managing director of S.A. Marine said: 'Michell offer the only hygrometers we have found to be reliable at UHP conditions.'