Vent Plugs with Filters and Check Valves can be used to relieve pressure or vacuum on bearing housings, gear boxes, reservoirs, or any application where venting is necessary.  Vent plugs assure pressure equalization and minimize undesirable problems, such as bearing seal blowout due to excessive pressure.  This vent plug allows air to communicate freely through a filter.  The check valve ball allows air to pass through in only one direction.  Pressure from the opposite direction immediately closes the valve, eliminating fluid loss.