208 MODERN PAPER-MAKING
source of heat. The cooling coil in the aspirator assists the suction pump by
condensing all steam and so avoiding back pressure.
Thus the system may be said to work on the counter-current principle.
The ingenious feature is that the cylinders are each arranged to work under
a graded scale of temperature, and steam from one cylinder is re-used, but
only in a position where the greatest benefit will result from its reduced tem-
perature. The use of steam evaporated under suction for the heating of the
low-temperatured cylinders is perhaps the most outstanding feature of the
system. The whole of the piping is arranged so as to allow easy release of
entrained air, and there are a sufficient number of cocks for this purpose.
Holmes andKingcome Steaming System (Fig. 84).—This steaming system is based
on the well-known principle of increasing the heat transference through any
heating surface by increasing the velocity of steam applied to the opposite side
of the surface; thus in the case of paper machines, the faster the steam is passed
through the cylinders the more heat is passed through the cylinder walls, con-
sequently giving increased drying power.
The method used to obtain maximum circulation coupled with economy
of steam is shown in diagram.
The steam is applied to three jets, the bulk passing through No. i jet which
feeds all cylinders except the first three. As there are no steam traps or other
restrictions in the piping, the steam passes straight through the cylinders and
exhaust pipes to the flood vessel, where the condensate is separated from the
steam, air and COs escaping to atmosphere from a release valve. The separated
steam is sucked off by No. i jet and blown through the cylinders again, and
the condensate is sucked up into the vacuum vessel by' No. 2 jet As water
under vacuum boils at a lower temperature, the condensate boils again in the
vacuum vessel and the steam given off is used to feed the first three cylinders,
the surplus being boosted up to main manifold pressure by No. 3 jet to be used
again.
The resulting condensatq left in the vacuum vessel falls down the fall-pipe,
which acts as a barometric leg, and trickles out of the sealing sump. As this
condensate has been under vacuum, its temperature is consequently very low.
Another valuable addition to this system is the use of an internal stationary
steam jet inside the cylinder, which blows steam direct on to the cylinder wall
at Sue pressure. By this method a still greater velocity as well as a drier cylinder
is obtained
All cylkwJers have to be very carefully balanced. A heavy side will cause a
joky niotbn, which makes the paper wrinkle or break. They are also graded
in Me, dimimsMiig towards the dry end to allow for the decreasing shrinkage
of die papa:.