The GLAM-GW (Gaillard and Lee, 1974; Altarelli and Maiani, 1974; Gilman and Wise, 1979) method of decoupling is applied to the flavour-conserving non-leptonic weak interaction mediated by W and Z exchange in SU(3)*SU(2)*U(1) to derive an effective Hamiltonian in which the weak bosons and the heavy quarks are decoupled. While the theoretical methods are quite general, numerical results for the effective Hamiltonian are given for a three-quark effective theory with u, d and s quarks active, since this is of interest for weak interactions in nuclear physics. Calculations are performed in the alpha =0 gauge and the ms subtraction scheme. The authors' numerical results are given for Lambda ₅(ms)=0.25 GeV and Lambda ₅(ms)=0.35 GeV.