1848 J. Sewell in (1850) I. 68 Regulator-cock, a cock placed to admit oil or tallow to lubricate the faces of the regulator.
1889 29 Mar. 231/2 A regulator-cock for the brake.
1911 F. N. Taylor xxxiii. 570 The degree of opening of the regulator cock, and..the rate at which water is passing through the apparatus.