The AOS is the 2nd stage in the separation of compressed air from the hydraulic oil (the first being the sump). While it looks like a larger oil filter, the cannister’s function is to filter out the hydraulic oil mist in the compressed air and return the oil to the compressor while the compressed air passes through the filter and heads on downline towards the hose line to mix with the solution to make CAF.
A tear in the AOS will allow oil to pass through the filter and on downline and out through the hose along with the CAF. This tear can be detected 2 ways – 1st – by regularly checking and operational monitoring the sump oil level (site glass). The oil level will drop. The 2nd method of detection is by placing your bare hand over the air only outlet during warm up checks. While some moisture is normal during the warmup check, oil is not. If the hand remains dry, oil is not passing by the AOS. If oil collects on your hand – immediately check the oil level, take the system out of service, and have your F-7 Certified EVT mechanic replace the AOS.
