Leakages at the point of insertion of the tubes are still generally
and exclusively repaired by means of roller apparatus for opening the
tubes, and with which an endeavor is made to tighten the latter in the
hole in the tube-plate.
The cones which were formerly employed injured the ends of the tubes by
splitting them; if the workman was not very skillful, the holes in the
plate became oval; and fractures likewise quite often occurred between
the holes in the plate itself.
The best apparatus to open the tubes are those in which the wedge that
separates the rollers is actuated by a screw; those in which the wedge
is driven in by a hammer are scarcely better than the old cones.
When apparatus for opening tubes are used, care must be taken to
begin with the external tubes, and to open these gradually. The
same operation is afterward performed upon the neighboring ones, in
approaching the center, and then the first ones are taken up. The
tubes should never be opened at one operation, but each one should be
subjected to several passes.
At the second pass, the rollers should be placed a little more deeply,
and should then be half within the tube-plate. The tube thus opens
behind the plate and forms a bearing against it, and this not only
renders it tighter, but also increases its adhesion to the plate.
Finally, the operation is finished by beating down the edge of the tube
that has been raised a little by the preceding pass. If this edge is
already somewhat deteriorated, or if it is not very thick, tightness
may be had by means of rings. The use of rings should be avoided as
much as possible, because they diminish the section of the tubes, and
render the cleaning of their interior more difficult. They should only
be employed as an exception, and should be considered as an unavoidable
evil. Even in old boilers, in which the holes have become oval, they
should be considered only as a means of rendering a small number of
tubes tight.