The invention relates to a valve having a closure element which is movable in an inner chamber and closes or clears a valve seat. The closure element is activated by a magnetic assembly in the magnetizable wall surrounding the inner chamber. According to the invention, the closure element has a low density. It comprises a hollow body having at least one activator body made of magnetizable material that is freely movable therein. The closure element has a low weight and a large surface. The large surface facilitates the resetting of the closure element on the valve seat by the action of the flowing medium.