A hydrocyclone for classifying aggregate material, comprising: a feed inlet; an inlet head in fluid communication with said feed inlet, said inlet head comprising: a generally cylindrical body portion, said body portion having a central vertical axis, a spiral inlet in fluid communication with said body portion via a body inlet, said body inlet comprising a terminal end of said spiral inlet, said spiral inlet having an inlet width measured between a first sidewall of said spiral inlet and a second sidewall of said spiral inlet, said spiral inlet having an inlet height measured between a lower surface of said spiral inlet and an upper surface of said spiral inlet, said spiral inlet having a cross-sectional inlet area along a plane extending through said central vertical axis, wherein an inlet angle is measured about said central vertical axis from an inlet opening of said spiral inlet along a travel direction of aggregate material entering said spiral inlet, wherein a ratio of said inlet height to said inlet width at said body inlet is between 2.8 and 3.2, wherein said inlet height increases with said inlet angle from said inlet opening to said body inlet, wherein said inlet width decreases with said inlet angle from said inlet opening to said body inlet; a vortex finder extending at least partially into said body portion of said inlet head; an overflow outlet in fluid communication with said vortex finder; and an underflow outlet in fluid communication with said body portion of said inlet head, said underflow outlet disposed beneath said body portion. a feed inlet; an inlet head in fluid communication with said feed inlet, said inlet head comprising: a generally cylindrical body portion, said body portion having a central vertical axis, a spiral inlet in fluid communication with said body portion via a body inlet, said body inlet comprising a terminal end of said spiral inlet, said spiral inlet having an inlet width measured between a first sidewall of said spiral inlet and a second sidewall of said spiral inlet, said spiral inlet having an inlet height measured between a lower surface of said spiral inlet and an upper surface of said spiral inlet, said spiral inlet having a cross-sectional inlet area along a plane extending through said central vertical axis, wherein an inlet angle is measured about said central vertical axis from an inlet opening of said spiral inlet along a travel direction of aggregate material entering said spiral inlet, wherein a ratio of said inlet height to said inlet width at said body inlet is between 2.8 and 3.2, wherein said inlet height increases with said inlet angle from said inlet opening to said body inlet, wherein said inlet width decreases with said inlet angle from said inlet opening to said body inlet; a vortex finder extending at least partially into said body portion of said inlet head; an overflow outlet in fluid communication with said vortex finder; and an underflow outlet in fluid communication with said body portion of said inlet head, said underflow outlet disposed beneath said body portion. a generally cylindrical body portion, said body portion having a central vertical axis, a spiral inlet in fluid communication with said body portion via a body inlet, said body inlet comprising a terminal end of said spiral inlet, said spiral inlet having an inlet width measured between a first sidewall of said spiral inlet and a second sidewall of said spiral inlet, said spiral inlet having an inlet height measured between a lower surface of said spiral inlet and an upper surface of said spiral inlet, said spiral inlet having a cross-sectional inlet area along a plane extending through said central vertical axis, wherein an inlet angle is measured about said central vertical axis from an inlet opening of said spiral inlet along a travel direction of aggregate material entering said spiral inlet, wherein a ratio of said inlet height to said inlet width at said body inlet is between 2.8 and 3.2, wherein said inlet height increases with said inlet angle from said inlet opening to said body inlet, wherein said inlet width decreases with said inlet angle from said inlet opening to said body inlet; a vortex finder extending at least partially into said body portion of said inlet head; an overflow outlet in fluid communication with said vortex finder; and an underflow outlet in fluid communication with said body portion of said inlet head, said underflow outlet disposed beneath said body portion.