We consider a class of dynamical systems that are described by time and space dependent partial differential equations. This class fits perfectly the port-Hamiltonian framework. We cover the wave equation, Maxwell's equations, the Kirchhoff-Love plate model, piezo-electromagnetic systems and many more. Our goal is to characterize boundary conditions that make the systems passive (the energy of solutions decays). This is done by constructing a boundary triple for the underlying differential operator. As a by-product we develop the theory of quasi Gelfand triples, which enables us to regard L2 boundary conditions even though the ``natural`` boundary spaces are neither included nor covering L2.