Method of making double wall storage tank for liquids

Claim 1

A method of manufacturing a rigid, double wall tank for storage of liquids from a rigid, single wall, cylindrical inner tank the outer surface of which has cylindrical sidewall portions of predetermined axial length and diameter and end portions extending generally transverse to said sidewall portions, said method comprising the steps of forming a male mold having a cylindrical configuration generally similar to the configuration of said inner tank, with the cylindrical sidewall outer portions of said mold having a diameter greater than said inner tank sidewall diameter, said mold cylindrical sidewall surface having a plurality of depressions each extending generally radially inwardly of said mold sidewall outer portions an average distance generally equal to half the difference between said diameter of said mold sidewall outer portions and said inner tank diameter; removably applying a moldable and hardenable material over said mold cylindrical sidewall portions and the depressions therein to form a substantially rigid sheath portion of a material that is substantially liquid tight and conforms generally to said mold sidewall surface and the depression therein, whereby is formed a cylindrical sheath portion having a generally cylindrical inner surface with a plurality of projecting extending generally radially inwardly thereof in general conformity with the mold depressions; removing said cylindrical sheath portion from said mold; introducing said cylindrical sheath portion over said inner tank with said projections engaging said inner tank cylindrical sidewall portions, whereby the radially inward projections of the sheath space the cylindrical inner surface of the cylindrical sheath portion from the outer surface of the inner tank to permit passage of liquid therebetween; and applying to the axial extremities of said cylindrical sheath portion substantially rigid and liquid tight sheath end portions overlying said inner tank end portions and extending generally transverse to said cylindrical sheath portion, whereby is formed a liquid tight sheath enclosing the inner tank, thus defining a double wall tank.

Claim 2

A method of manufacturing a rigid, double wall tank for storage of liquids from a rigid, single wall, cylindrical inner tank the outer surface of which has cylindrical sidewall portions of predetermined axial length and diameter and end portions extending generally transverse to said sidewall portions, said method comprising the steps of forming a male mold having a cylindrical configuration generally similar to the configuration of said inner tank, with the cylindrical sidewall outer portions of said mold having a diameter greater than said inner tank sidewall diameter, said mold cylindrical sidewall surface having a plurality of depressions each extending generally radially inwardly of said mold sidewall outer portions an average distance generally equal to half the difference between said diameter of said mold sidewall outer portions and said inner tank diameter; removably applying a moldable and hardenable material over said mold cylindrical sidewall portions and the depressions therein to form a substantially rigid sheath portion of a material that is substantially liquid tight and conforms generally to said mold sidewall surface and the depression therein, whereby is formed a cylindrical sheath portion having a generally cylindrical inner surface with a plurality of projecting extending generally radially inwardly thereof in general conformity with the mold depressions; removing said cylindrical sheath portion from said mold; introducing said cylindrical sheath portion over said inner tank with said projections engaging said inner tank cylindrical sidewall portions, whereby the radially inward projections of the sheath space the cylindrical inner surface of the cylindrical sheath portion from the outer surface of the inner tank to permit passage of liquid therebetween; and applying to the axial extremities of said cylindrical sheath portion substantially rigid and liquid tight sheath end portions overlying said inner tank end portions and extending generally transverse to said cylindrical sheath portion, whereby is formed a liquid tight sheath enclosing the inner tank, thus defining a double wall tank.