but is utilized for spreading the pulp in the compartments fig6 shows an additional device arranged either in connection with the pressure chamber 22 itself or with the feed duct 24 communicating with the pressure chamber 22 the device 60 comprises a pressure balancing chamber 62 for compensating the pressure pulses created in the apparatus during the feeding of pulp therein it has been found out that the pressure in the treatment compartment and accordingly in the pressure chamber 22 rises due to the pump pressing pulp towards the chamber the pressure however drops suddenly as a new empty treatment compartment turns towards the pressure chamber and opens thereto revealing an open space therein by arranging said pressure balancing chamber 62 as described earlier the pump is able to push pulp into the chamber 62 against gas pressure whereby the pressure in the pressure chamber 22 does not rise that high the upper portion 64 of the pressure balancing chamber may be filled with air or some other appropriate gas said portion may be in direct communication with the pulp or it may also be separated therefrom by means of rubber bellows or like device 66 when using the apparatus according to the invention for feeding pulp to a drum type washer for example it is possible to utilize the surface of the drum better in the actual washing process because the feed and discharge apparatuses cover only 60 u00b0 degrees of the entire drum circumference which leaves thereby 300 u00b0 degrees for washing presuming that the thickness of.