In this paper, an equivalence on the class of nullnorms on a bounded lattice is discussed. Some relationships between the U and V-partial orders are investigated. A necessary and sufficient condition making a bounded lattice also a lattice w.r.t. the V-partial order is given. Moreover, the relation between the algebraic structures related to the U and V-partial orders is studied. (C) 2017 Elsevier B.V. All rights reserved.