The present invention relates to a front cover of target frames of dartboards with a tidy appearance and a long service life, which comprises a cylindrical housing frame provided with a flange at the bottom edge used for connection. The float member is coupled to the tank for movement between a first position and a second position. The first filter layer comprising a plurality of fibrillated electrostatically charged electret fibers forming a nonwoven web; the first filter layer having a total pressure drop between about 0.