SUCTION 185

water, and up till recently very little attention seenis to have paid to

this point.

There is a tendency, however, nowadays for a large suction pump to be
employed with a large receiver between the boxes and the pump. The bottom
of this receiver has a drain-pipe leading to a water pump which draws the
water away from the receiver as It enters from the boxes, and leaves the air
pump to deal only with air, which is drawn out from the top of the receiver.
By adopting this method a much more satisfactory vacuum is obtainable, and
when the vacuum Is altered on any one box It does not affect the others as
readilv.

\Jamcs Atnerton (Sycamore) Lfl.
FIG. 67.—VAKOUS TYPES OF SECTIONS OF SUCTION Box TOPS
There Is also another method in which barometric legs or syphon pipes
are used In the system for the withdrawing of water.
We are still of the opinion that to have infinite control .over the sheet when
making fine papers, a separate vacuum to each box is The chief
difficulty, however, is to get a sufficiently small pump, which Is so constructed
that It will stand up to die long hours of usage necessary on a paper machine,
and deal equally effectively with air and water.
Some machines still have steam ejectors on thek vacuum boxes in place of
air pumps, and these give excellent results, but they are extravagant in steam,
and they are sometimes blamed for being responsible for making pin-holes in *
the paper. The least costly arrangement Is to employ a barometric leg, and
where the machine is built on the first floor and has a deep basement, it seems
that there should be no difficulty in adopting this method, especially as die.