Liquid dosing device to be mounted on a container for dispensing doses of liquid from said container said dosing device comprising: - a dosing chamber, said dosing chamber having a front end and a back end opposite to the front end; - an outlet passage located at the front end of said dosing chamber; - a plunger located in the dosing chamber and dividing the dosing chamber in a front space and a back space, said plunger being moveable in the dosing chamber between a forward position in which the plunger closes off the outlet passage and the front space has a minimal volume, and a backward position, in which the front space has a maximal volume; - a dosing chamber inlet passage providing a fluid communication between the front space and the container in each position of the plunger, to allow liquid to flow from the container to the front space; - a timer passage (16; 11D) associated with the dosing chamber providing a fluid communication between the container and said back space in each position of the plunger, to allow liquid to flow from the container to the back space; - a release passage associated with the dosing chamber, said release passage being greater than the timer passage (16; 11D) and providing a fluid communication between the back space of the dosing chamber and the container to allow liquid to flow from the back space to the container; - a valve assembly associated with the release passage, said valve assembly having a closed state in which the release passage is closed off and an open state in which said release passage is open and fluid is allowed to flow there through from the back space to the container; characterized in that the valve assembly comprises a valve seat located at the back end of the dosing chamber and a membrane located on a side of the valve seat facing away from the back space, said membrane being made of an elastic foil having a uniform thickness, said membrane having a stationary portion that is fixed with respect to the valve seat and at least one moveable flap which is connected to the stationary portion by a hinge portion, wherein said flap in said open state of the valve assembly is moved away from the valve seat and in said closed state of the valve assembly bears against the valve seat, and wherein the hinge portion has an elastic property and is elastically flexed when the flap is moved away from the valve seat and is in a rest state when the flap bears against the valve seat, and wherein the the flap has a relatively low weight such that it is ensured that the flap in the rest state bears against the valve seat, independent of the orientation of the liquid dosing device. - a dosing chamber, said dosing chamber having a front end and a back end opposite to the front end; - an outlet passage located at the front end of said dosing chamber; - a plunger located in the dosing chamber and dividing the dosing chamber in a front space and a back space, said plunger being moveable in the dosing chamber between a forward position in which the plunger closes off the outlet passage and the front space has a minimal volume, and a backward position, in which the front space has a maximal volume; - a dosing chamber inlet passage providing a fluid communication between the front space and the container in each position of the plunger, to allow liquid to flow from the container to the front space; - a timer passage (16; 11D) associated with the dosing chamber providing a fluid communication between the container and said back space in each position of the plunger, to allow liquid to flow from the container to the back space; - a release passage associated with the dosing chamber, said release passage being greater than the timer passage (16; 11D) and providing a fluid communication between the back space of the dosing chamber and the container to allow liquid to flow from the back space to the container; - a valve assembly associated with the release passage, said valve assembly having a closed state in which the release passage is closed off and an open state in which said release passage is open and fluid is allowed to flow there through from the back space to the container; characterized in that the valve assembly comprises a valve seat located at the back end of the dosing chamber and a membrane located on a side of the valve seat facing away from the back space, said membrane being made of an elastic foil having a uniform thickness, said membrane having a stationary portion that is fixed with respect to the valve seat and at least one moveable flap which is connected to the stationary portion by a hinge portion, wherein said flap in said open state of the valve assembly is moved away from the valve seat and in said closed state of the valve assembly bears against the valve seat, and wherein the hinge portion has an elastic property and is elastically flexed when the flap is moved away from the valve seat and is in a rest state when the flap bears against the valve seat, and wherein the the flap has a relatively low weight such that it is ensured that the flap in the rest state bears against the valve seat, independent of the orientation of the liquid dosing device.