a flow regulating device comprises a chamber forming element covered by a tube of elastomeric material , which together form a flow passage leading from an inlet port to an outlet port . the flow passage forms a first flow chamber which is partly defined by the elastomeric tube and which is configured such that flow of fluid through the chamber causes inward deflection of the tube and thus constricts the flow cross section of the first flow chamber . the flow passage further forms a second flow chamber downstream of the first flow chamber , the second flow chamber being partly defined by the elastomeric tube , and the configuration being such that flow of fluid through the second flow chamber causes the tube to deflect inwardly and thus constrict the flow cross section of the second flow chamber . in one embodiment the arrangement is such that vortex flow is induced in each of the flow chambers . in a further embodiment , the flow connection between the first and second flow chambers is provided by a tortuous flow passage .