This paper addresses the computation of the steady state behaviour of a subclass of continuous Petri nets under infinite servers semantics. For this class, the visit ratio is fixed by the net structure and the rates associated to the transitions. The class generalises well known net subclasses, as marked graphs or equal conflict net systems. A programming problem allows to obtain a tight bound of the throughput in the steady state. Its relaxation leads to a linear programming problem (LPP) that, for particular net subclasses, provides the exact value. Some of the “paradoxes” (essentially non-monotonicities) that the behaviour of those models may exhibit are pointed out.