A valid inequality α T x ≥ α0 for a set covering problem is said to have pitch ≤ π (π a positive integer) if the π smallest positive αj sum to at least α0. This paper presents a new, simple derivation of a relaxation for set covering problems whose solutions satisfy all valid inequalities of pitch ≤ π and is of polynomial size, for each fixed π. We also consider the minimum knapsack problem, and show that for each fixed integer p > 0 and 0 < ǫ < 1 one can separate, within additive tolerance ǫ, from the relaxation defined by the valid inequalities with coefficients in {0, 1, . . . , p} in time polynomial in the number of variables and 1/ǫ.