A diaphragm device for a check valves is provided. The diaphragm device comprises a diaphragm, adapted to cover at least one orifice, and an operation device, adapted to enable movement of the diaphragm substantially along a length axis of the orifice. The operation device comprises at least one first operation organ and at least one second operation organ. The first and second operation organ in turn each comprises a first portion, and a second portion. The first portion of the first operation organ is adapted to be connected to a check valve housing, and the second portion of the first operation organ is connected to the second portion of the second operation organ. Furthermore the first portion of the second operation organ is connected to the diaphragm and the second portion of the second operation organ is connected to the second portion of the first operation organ. The first operation organ is movable in relation to the second operation organ, and the second operation organ is movable in relation to the diaphragm, for enabling movement of the diaphragm, substantially along the length axis of the orifice. This embodiment could enable the check valve to open a relatively long way by means of a relatively low pressure or flow, at the same time as the deformation of the resilient material could be relatively small since it is deformed in a multiplicity of points and along a relatively long extension of resilient material.