The invention relates to a membrane (17) completely covering an opening (13) giving access to a space in a device which membrane (17) is made of an elastic material penetrable by a needle, the membrane (17) is fastened around the opening (13) and the membrane (17) protrudes from the opening (13) and forms an air filled volume in front of the opening (13) which air filled volume can be reduced in size when a pressure is put on the membrane (17) from the outside, the inner surfaces of the membrane (17) define a passage (17a) at the first closed end of the membrane (17) through which a needle (19) can pass and the second end of the membrane (17) is adapted to attach the membrane (17) to a holding part (61). The walls of the membrane (17) have a thickness and shape of the chosen membrane material making it possible, to maintain the protruding shape in a use position without the outer surfaces of the membrane (17) are supported with walls of rigid material. Also the invention relates to a device in which the membrane is used, and a kit where this device is combined with a corresponding unit.
