Improved Construction of Capping, Adaptable for use as a Chimney Top or as a Ventilating Cowl or Exhauster.
Year: 1890

page_text: Date of Application, 11th Oct., 1890
Complete Specification Left, 19th Mar., 1891-Accepted, 25th Apr., 1891
PROVISIONAL SPECIFICATION.
Improved Construction of Capping, Adaptable for use as a Chimney
Top or as a Ventilating Cowl or Exhauster.
I, CHARLES MITCHELL, of 83, Pomeroy Street, Hatcham, Surrey, Tin Plate
Worker, do hereby declare the nature of my said invention to be as follows:-
The object of this invention is a capping adaptable either for use as a chimney
top, or as a ventilating cowl or exhauster, its construction being such that the force
of the wind or outside air currents is utilized to withdraw or suck out the smoke or
the vitiated air from the chimney or ventilating shaft as the case may be, and thus
not only preventing downdrafts when a strong wind is blowing but also creating
an updraft which forces out the smoke or air from the shaft or chimney instead of
pocketing it or boxing it up as is the case with the chimney tops or cappings at
present in usc.
My improved capping is constructed as follows:-The lower part which fits over
the top of the shaft or chimney is formed in the shape of a louvre at an angle of
about 45 degrees upon which a vertical cylindrical cap is supported, a slight
clearance being allowed between the top of the louvre and the under edge of the cap.
Within the cap is a horizontal dise preferably made of two pieces joined at their
edges, said disc being a little larger than the opening of the louvre and chimney
top but not so large in diameter as the inside of the cylindrical cap thus leaving a
space between the sides of the cap and the edge of the disc.
The disc is convex or domed both on its under and its upper surfaces, the effect
of which is to guide the wind coming from above the capping down around the
disc on to the louvre beneath, against which it strikes and rebounds upwards into
and out of cap, drawing with it the smoke or air from the chimney or shaft.
10th October 1890
C. MITCHELL. A
COMPLETE SPECIFICATION.
Improved Construction of Capping, Adaptable for use as a Chimney
Top or as a Ventilating Cowl or Exhauster.
I, CHARLES MITCHELL, of 83, Pomeroy Street, Hatcham, Surrey, Tin Plate
Worker, do hereby declare the nature of my said invention, and the manner in which
the same is to be performed, to be particularly described in and by the following
statement :-
The object of this invention is a capping adaptable either for use as a chimney
top, or as a ventilating cowl or exhauster, its construction being such that the force
of the wind or outside air currents is utilized to withdraw or suck out the smoke or
the vitiated air from the chimney or ventilating shaft as the case may be, and thus
not only preventing downdraughts when a strong wind is blowing but also creating
an updraught which forces out the smoke or air from the shaft or. chimney, instead
of pocketing it or boxing it up, as is the case with the chimney tops or cappings at
present in use.
My improved capping is constructed as follows:-The lower part which fits over
the top of the shaft or chimney is formed in the shape of a louvre at an angle of about
45 degrees, upon which a vertical cylinder is supported, a clearance being allowed
between the top of the louvre and the under edge of the cylinder. This clearance
or space plays an important part in the construction of my capping and is a feature
which contributes greatly to its practical utility.
Within the cylinder is a horizontal disc preferably made of two pieces joined
nearly at their edges, the top part of the disc being the larger to allow the rain to

page_text: drop off, and also a little larger than the shaft or chimney top but not so large in
diameter as the inside of the cylinder thus leaving a space between the sides of the
cylinder and the edge of the dise to allow the smoke or vitiated air to pass out.
The disc is convex or domed both on its under and its upper surfaces, or it may
be conical on its upper and flat on its under surface, the effect of which is to guide
the wind, when coming from above the capping, down past the disc on to the
louvre beneath which guides or deflects it away from the mouth of the chimney
drawing or sucking out the smoke or air from it by the strong upward draught it
creates or induces in the chimney or shaft as it escapes, the smoke and the wind
current passing out together.
My improved capping and its mode of application is illustrated in the annexed
drawings in which Figure 1, Sheet 1, is a section, Figure 2 an elevation of Figure 1,
Figure 3 a half sectional elevation of a double action capping; Figures 4 and 6,
Sheet 2 are sections through the elevations Figures 5 and 7, of ventilators as applied
to a building where a large amount of ventilation is required such as for Board
schools, public buildings and halls, and the ventilators may if desired be extended
for the whole length of the roof in the case of factories, laundries, workshops, engine
sheds and the like.
Referring to Figures 1 and 2, A is the portion which fits over the chimney or
shaft and carries a louvre B which by means of strong stays C supports a vertical
cylinder D, the lower edge E of which is raised sufficiently above the top edge F
of the louvre as to allow a clearance or space between them for permitting a free,
uninterrupted passage for the wind horizontally from one side through to the
other side and cause an induced upward current from the chimney or shaft which
withdraws the smoke or vitiated air.
I find from practical tests I have made with the aid of a number of carefully
measured models that the amount of space or clearance just referred to, which gives
the best results is about that shown in the drawings in proportion to the other parts
of the capping, the parts being shown in about the respective dimensions they would
bear to each other, but I may sometimes vary them to suit circumstances, such for
example as when a stack of chimneys are ranged side by side, in which case the
louvre and the cylinder may be reduced in diameter to permit the chimney tops
being placed close together.
Within the cylinder D is the double convex disc G supported by suitable stays H,
the edge of the upper part of the disc projecting beyond the lower part in order to
carry off rain and prevent it running round the under side and dropping down the
chimney or shaft.
The disc G, as before explained, is made a little larger than the mouth of the
shaft so as to stop direct action of the wind onto the shaft, but a space is left all
round it between the sides of the cylinder and its edge to allow the sinoke to escape
upwards, or for the wind coming vertically down from above the capping to pass
downwards past the contracted part of the cylinder, on to the louvre B which guides
it away from the mouth of the shaft A causing a strong updraught in the latter as
it escapes and effectually drawing out the smoke or vitiated air as the case may be.
In some cases the disc G may be extended or continued upwards to a long point
if desired and finished by an ornamental finial such as an arrow or a cross.
This
arrangement would be very suitable for churches, chapels or where an ornamental
appearance is desirable.
The cylinder D may have a scalloped or other shaped fancy edge I preferably
cut out from the same piece of material, and a strengthening band J round its upper
part, its lower edge being formed with a beading K.
Figure 3 shows an arrangement in which a double action is obtained, the parts
being in all respects the same as in the preceding figures, except the disc which in
this case extend upwards in the form of a truncated cone G open at both ends
but having a weather cap L above the top supported by suitable stays, the inne
part M of the cap being convex to deflect the smoke outwards. The upper par
of this cap may be dome shaped if desired instead of a cone as shown.

page_text: It will be observed in these figures, which show my capping as arranged for
either a chimney top or a ventilator, that there is ample room for a sweep's brush
to pass out clear of the mouth of the chimney.
My improved capping may be fixed in any position where smoke or foul air is
required to be exhausted and in Figures 4 and 6 Sheet 2 (which are sections through
the elevations Figures 5 and 7 looking from their ends) I show the manner of
applying my capping or exhaust ventilator to the roof of a building at the ridge.
In these views the parts are marked with letters corresponding to those of the
same parts in the previous figures and can be readily referred to, Figures 4 and 5
representing the form described with regard to Figures 1 and 2 of Sheet 1, and
Figures 6 and 7 that of Figure 3, Sheet 1.
It will be observed that the shaft portion A is in these cases dispensed with, the
outlet for the vitiated air being by an aperture F in the roof forined by cutting
away the ridge at the apex as shown the rafters being framed together by short tie
beams at intervals.
In constructing new buildings there would be considerable saving by this plan as
the ridge and top ends of rafters would not be required. The portion D would also
be modified, and would no longer be cylindrical but oblong in shape as shown, and
the part G would likewise be extended in length.
In these arrangements the louvre B would not require to be made, as it is formed
naturally by the sloping sides of the roof as may be seen in the drawings Figures 4
and 6, but the roof at this part may be covered in by lead or zinc. The open part
of the ventilator may be enclosed by a screen N of wirework or other, to prevent
the entry of birds.
In the drawings Figures 5 and 7 the ventilators are shown as affixed to a portion
only of a roof but it is obvious that they may be extended to the full length of the
roof.
The views shown are only a few examples of the application of my improved
capping, but it is evident that the patterns and the shapes shown may be varied to
suit taste or circumstances, as they may be made round, oral, square, oblong or
other shape, and of any suitable material such as zinc, or earthenware.
This improved capping requires no air inlets or other similar arrangements to
assist its action as is generally required by those at present in use, its construction
being so calculated that it performs its work thoroughly and efficiently without any
such aid.
Having now particularly described and ascertained the nature of my said inven-
tion, and in what manner the same is to be performed, I declare that what I
claim is:-
1. The improved construction of capping adaptable for use as a chimney top or
as an exhaust ventilator, comprising the shaft A and louvre B so arranged with
relation to the part D that the upper edge of A and B stands away clear of the
lower edge of D leaving a clearance between them for the free uninterrupted
passage of the wind from one side to the other causing an induced updraught in the
chimney or shaft if the wind strikes the capping horizontally, in combination with
the cylindrical portion D and the disc G for creating an updraught in the shaft
should the wind strike downwards from above, the whole arranged as described
and substantially as shown in the drawings Figures 1 and 2.
2. The modified construction of double action capping described with reference
to Figure 3 of the drawings.
3. The arrangements shown in Figures 4, 5, 6, and 7 in which the ridge portion
of the roof is dispensed with, thereby effecting a saving in material especially in the
case of new buildings.
001
C. MITCHELL.