04 AMT
Historically there has been 2 types of compressed air dryers
used in rail applications. These are desiccant dryers and
membrane dryers. They offer different approaches to the
issue of removing moisture and contaminants from the air.
The problem with current
air drying solutions
» Collect and absorb water using special canisters filled
with beads, held together with a clay substance
» The beads absorb moisture and contaminants from
the air, so dry air flows out to the vehicle
» However, vibration can cause the beads to rub together,
producing dust that contaminates the air
» As the beads erode their efficiency and performance
is reduced, and the pressure drop can increase
» Over time the substance in the canister can become over
saturated, and a chemical reaction causes irreparable damage
to the beads, which means they cannot be used again
» Use special fibre tubes suspended between two potted
ends to form a semi-permeable membrane
» Water vapour passes through the membrane wall via plasmolysis and
is swept into a small vent, which releases it back into the atmosphere
» Contamination, such as oil, can clog and damage
the fibres, causing them to break
» Membrane dryer fibres are delicate and can be easily
damaged or broken in harsh applications
» If one fibre breaks, the others usually follow shortly
after, causing a catastrophic failure
Desiccant dryers Membrane dryers
Each technology has its
strengths, but it's also
acknowledged that neither
option currently offers a wholly
satisfactory or reliable solution.
