A pressure swing adsorption (PSA) including a first PSA module having a first manifold, a second manifold, and a plurality of pressure vessels extending between the first manifold and the second manifold. The unit further includes at least one support member attached to one of the manifolds and configured to provide rigidity thereto. The support member is preferably made of a material different from the manifold to which it is attached. The PSA unit can also include a structure for clamping the plurality of pressure vessels between the first manifold and the second manifold without imposing a bending moment to the vessels.