A NEW OR IMPROVED CONSTRUCTION OF CHIMNEY COWL OR CAN
Year: 1880

page_text: PROVISIONAL SPECIFICATION left by Alexander Thomson and Robert
Anderson at the Office of the Commissioners of Patents on the 4th November
1880.
ALEXANDER THOMSON and ROBERT ANDERSON, both of Glasgow, in the County
of Lanark, North Britain. "A NEW OR IMPROVED CONSTRUCTION OF CHIMNEY
COWL OR CAN."
This Invention relates to a new or improved construction of chimney cowl or
can, to be fitted on the tops of house chimneys, for the purpose of improving their
draught, or aiding ventilation, and for preventing back draught or blow down of
smoke by the wind. The improved cowl is also much simpler in design, less
expensive in first cost, and less liable to get out of repair or working order, than
chimney cowls hitherto in use.
The improved chimney cowl is formed by preference in two parts, the lower of
which greatly resembles an ordinary plain chimney can, being cylindrical or slightly
conical, tapering upwards, and being either fitted on the top of the usual can, or
made of earthenware, and made to form the chimney can itself; but in either case
being made or fitted with several (as two, three, or more) short tubular ducts
entering and leading into the can or lower part of the cowl at different positions
round its circumference, in an upwardly angled or highly inclined manner, so that
the wind striking the roof of the house and being deflected upwards therefrom,
would enter these ducts or tubes in a straight line and pass directly upwards in
and through the can or cowl.
The upper part of this cowl or cam, which may be of galvanized iron or other
metal, is fitted with, or has formed on it, a hood or top piece, open at top and
bottom, and attached to the top of the can portion by a fixed or movable sliding
ring, with transverse or radial feathers or webs; and this hood is made of a
conoidal shape, considerably larger in diameter at the bottom where it is fitted to
the can, so as to leave an annular passage for air all round the latter, but reduced
to about the same diameter as the can at its upper end. In the top piece or hood,
there is hung or otherwise fitted a movable conical deflector, which is made flat on
its lower side or bottom, and tapered at its upper side, and is placed so that its
lower surface reaches down to within a few inches of the can or lower part of the

page_text: cowl, leaving an annular space for the smoke to rise round it out of the chimney;
whilst the upper or conical surface is tapered to be at about a tangent to the
upward curvature of the hood, so that in the event of the wind blowing down
through the upper end of the hood, it would glide off the surface of the cone,
between it and the inner surface of the hood, and down through the annular air
space outside the can or lower part of the cowl, no blow down being allowed to
pass inwards into the annular smoke passage or chimney. This conical deflector is
also made preferably larger in diameter than the upper end of the lower can or
cowl, so that rain falling into the hood would be carried over the edge of or outside
the lower smoke can. The deflector may be suspended by a vertical rod attached
to it, passing through or held by a transverse bar carried on small brackets, or a
supporting ring inside the hood or top of the cowl, so as to be easily withdrawn or
removed when the chimney is to be swept, without the necessity of lifting off the
hood, or whole of the upper part of the cowl as usual; although this may also be
removed or lifted off when desired or preferred.
A concave, convex, or flat sheet-iron plate is also by preference fitted a short
distance over the whole hood or cowl, to break the downward force of the wind
tending to enter the cowl, but leaving a few inches clear between it and the cowl
for the passage of the smoke. This plate may be held by two, three, or more stems
fixed to it, and to a movable ring passing over or inside the upper part of the hood,
so that it may be readily removed also for sweeping the chimney. The rod of the
conical deflector below may be attached if desired to this upper plate or cap
instead of being carried by a separate bar or ring.