Submersible battery vent plug

Claim 1

A submersible battery vent plug comprising a tubular body having an externally threaded lower portion adapted to be received in a threaded opening in a battery cover; interior wall means within the body dividing the interior thereof into a upper and a lower chamber with an interconnecting axially extending opening, the wall means including a downwardly projecting portion surrounding the lower end of the opening and an upwardly projecting portion having an annular top surface surrounding the upper end of the opening, the interconnecting opening having upper and lower tubular portions with the upper portion having a diameter greater than that of the lower portion and a downwardly sloping interior wall section between the upper and lower portions; the body having at least one fluid drain opening connecting the bottom of the upper chamber with the exterior; and a valve stem having a resilient upper sealing portion adapted to fit the annular top surface of the interior wall means, a middle portion with a diameter smaller than that of the upper portion of the interconnecting opening, a lower portion with a diameter smaller than that of the lower portion of the opening, and a downwardly convex lower sealing portion between the middle and lower portions, the length of the middle section being less than the axial distance between the annular top surface of the interior wall means and the downwardly sloping interior wall section of the interconnecting aperture, the valve stem being positioned with its middle and lower portions vertically movable within the interconnecting opening and adapted to allow the upper sealing portion to make sealing contact with the annular top surface under the influence of any initial fluid pressure in the upper chamber and to allow the lower sealing portion to make sealing contact with the downwardly sloping wall interior section as the upper sealing portion is deformed by a fluid pressure greater than the initial pressure.