Hydraulic Air Breather filters whose whole name is Hydraulic oil tank air Breather valve Filter, are placed on hydraulic reservoirs tank to prevent atmospheric contamination and water from entering. Air enters the reservoir whenever the fluid level drops. This occurs during normal cycling of the machine when fluid cools down during idle periods. Hydraulic tank filters are designed to stop particles larger than 3 µm from entering the system. This is a sensible, affordable solution for any hydraulic system. It is the best complement of the hydraulic filters. They hydraulic oil tank and hydraulic pump will be broken or bad when the air breather valve filter is blocked.