184 MODERN PAPER-MAKING

the frame of the machine. Each box has a valve to regulate the suction
admitted by the pipe, and a small pipe comes from the centre of the box to the
fore side and is used as a fine adjustment for admitting air to the box. The
space between the movable and fixed ends is kept full of water to prevent air
leakage, and sometimes the suction may be kept more steady by, in addition,
a packing of soft doctor broke.

There is another type of box, used chiefly on 'news' machines, which has
one solid board forming the top. This board is drilled with holes or slits en
echelon, and has movable ends of expanding rubber.

The ideal method of operating suction boxes is to have a separate pump

\]amts Atherton (Sycamore) Ltd.
FIG. 66.—NEW TYPE 'VULTURE' VACUUM Box TOPS, WITH 'END ON* GRAIN FOR LONG WEAR
The top is in sections which can be easily fitted
for each suction box. This is especially the case where other results besides
the removal of water are required.
Where a dandy roll is used, it is absolutely essential that there should be
/a very fine control of the suction box immediately in front of the dandy.
Hiis is necessary even with a plain roll when it is important to get a fine, clear-
looking sheet; but it is more important still when water-mark designs have
to be put iatx> the paper. The usual method is to have one suction pump for
all the fxxraes, up to even five or six, and to rely on regulating the vacuum on
gaae or two of die boxes, in order to control the sheet This is not satisfactory,
,bccanse ihe moment the vacuum is altered on one box it is automatically
dtcral oft aB the others,
Tlie suction pump attached to vacuum boxes has to deal not only
with air passing through the sheet, but also with a large quantity of