The invention relates to a single seal, and more specifically to a seal for a rotary shaft extending through a wall, e.g. that of a pump housing. The single seal exhibits one single sealing location between a stationary and a rotating sealing ring. The seal is attached by means of a flange (12) on to the wall in order to seal off a chamber inside the wall against the shaft (22) and towards the exterior. According to the invention, the sealing rings (1, 2) are biased against each other by means of an axially movable member (5) extending through the wall in order to increase the contact between the sealing rings (1, 2). The resilient member may be a slitted sleeve (5) or a coil spring.