Abstract: In a sampler for sampling a first portion of a liquid flow, the liquid flow enters at a sampler inlet (12). The sample passes through a valve (30) into a sample chamber (8) and then the valve closes, diverting the remainder of the liquid flow to a sampler overflow (6). The valve comprises a valve inlet (24) coupled to the sampler inlet, a valve outlet (38, 36) opening into the sample chamber and positioned, in use, substantially below the valve inlet, a shut-off chamber (32) separating the valve outlet from the valve inlet, and a valve overflow (34) leading from the shut-off chamber to the sampler overflow (6). When the liquid level in the sample chamber rises to a predetermined level it disrupts the flow of liquid through the valve outlet and diverts later flow through the valve inlet into the shut-off chamber and through the valve overflow.