The cleaning mechanism (13) for a paper pulp sample taker, to rinse the components where the pulp has been in contact between samplings, has components (19,31,33,34) which are opened by the pressure of the cleaning agent, and which can be closed against this pressure. The cleaning mechanism (13) is a non-return valve assembly built into a rinsing unit (15), fitted to the housing (1) of the sample taking appts. to connect to its interior, positioned to deliver a stream of rinsing fluid to the shaft-type section (3) used to extract a pulp sample from the pulp processing zone, when it is in the inoperative position. A disc (18), in the opening (17) of the rinsing unit (15) for the cleaning mechanism (13), carries the components (19,31,33,34) to open and close the flow. The flow of the rinsing agent is a ring stream through the ring gap formed between the opening (17) and the disc (18). A rod (31) extends from the disc (18) along the line of the rinsing unit (15) to close the components (19,31,33,34) of the cleaning mechanism (13), fitted with a spring (19) to press the disc (18) against the opening (17) of the housing (1). ADVANTAGE - The mechanism gives a simple and reliable cleaning action, between samples and at given intervals, in a simple and reliable appts..