vertical walls 7 and 9 joined by a bottom portion 11 the inside surface of wall 3 and the outside surface of wall 7 are contoured so as to provide a vertical chamber 12 of steadily diminishing cross section culminating in a non return valve formed by wipers 13 and 15 a second chamber 17 formed by walls 3 and 9 going from bottom to top has a cross sectional area which steadily increases as will be seen below the fluid passing from chamber 12 to 17 has a maximum velocity at the valve formed by wipers 13 and 15 and one formed by a wiper 18 thus obviating the possibility of spent liquor reversing flow as it enters through an inlet 19 in delay tank 5 and flows into chamber 12 through an opening 21 positioned under the delay tank 5 is a bottom roller 23 cooperating with the wiper 18 and positioned on an axle 25 an inlet roller 27 is secured to an axle 29 while an outlet roller 31 is secured to an axle 33 such that tangential lines from roller 27 to roller 23 and from roller 23 to roller 31 are substantially vertical in this manner sliver can be continuously drawn over roller 27.