268

MODERN PAPER-MAKING

controlling the basis weight of the paper being made. The valve itself should
preferably be specially designed so that a large number of turns are required
to change the setting from the shut to the full-open position. This will give
greater delicacy of control, and therefore more accurate basis weight adjust-
ment, than can be obtained from a valve that requires only a few turns to

[Vickerys, Ltd., and Walmsleys (Bury), Ltd.
FIG. 114.—LATEST TYPE OF HIGH-CAPACITY BIRD SCREEN FOR NEWSPBINT STOCK
The lower motor operates the shake motion and the upper motor drives the gearing which keeps the cylindrical
screen turning slowly round
produce a large change in the rate of flow. The diluted stock from the mixing-
pump passes direct to the strainers which, usually, are located behind the
breast box.
The strainers needed for news stock must, of course, be of large capacity.
The type used (see Fig. 49) is that known as the inward-flow strainer, because
the stock is pumped to an outer container and flows by gravity through the
slits of the screen to the centre. The screen itself is a large cylinder in which.
thousands of slits, parallel with one another and in rows, are cut. The usual
width of slit for news is about 0.0025 inch. In operation the stock is helped.