GB2100849A - Chimney cowl - Google Patents

Abstract

A chimney cowl unit comprises a pipe (10) which fits onto the chimney and a cowl pipe (20) arranged to turn about the vertical axis of the pipe (10). The cowl pipe has an exit (24) and surrounding this is a cowl (26) with tapered sections forming a choke (30) for creating a venturi effect in the zone surrounding the exit (24). <IMAGE>

Description

SPECIFICATION Improvements in or relating to cowl units This invention relates to a cowl unit, which will hereafter be referred to as a chimney cowl unit, although it is to be understood that the cowl unit is equally suitable for attachment to other exits for waste and/or spent gases such a flues and ventilators.

Known forms of cowl unit include designs with fixed components in relation to the chimney, wherein pipes are branched to form a configuration of flat discs shaped as shallow cones or the like. Other designs have a cowl assembly which moves in relation to the chimney, such as the cowl units known from U.K. Patent Specifications No. 275977 and No. 548568. In these designs, a cowl assembly is pivotally mounted to a chimney pipe to swing into the wind, and wind air is drawn in to create a venturi effect in a central zone around which the chimney gases are exhausted. Thus, the general form of the cowl assembly in such known designs is that of a throated cowl fitted coaxially within a cowl pipe which is pivotally mounted to the chimney pipe.

Designs of the latter mentioned kind, altnough generally more efficient than the first-mentioned kind, have the disadvantage that, at high wind speeds, e.g. gale or near-gale force winds, the venturi effect tends to break down, and the cowl unit ceases to operate satisfactorily.

It is an object of this invention to provide an improved chimney cowl unit which remains efficient in operation even at high wind speeds.

According to the invention, there is provided a chimney cowl unit comprising a chimney pipe adapted for attachment to a chimney to receive chimney gases, and a cowl assembly pivotally mounted to the chimney pipe freely to turn about the axis of the chimney pipe, said cowl assembly including a cowl pipe for receiving gases from the chimney pipe and a cowl mounted to said cowl pipe to surround the exit of the latter, the cowl being open to receive the wind and having a throat section for creating a venturi effect in the wind air in an annular zone surrounding the exit of the cowl pipe.

Thus, at the root of the invention lies the discovery that the known designs of venturi-effect cowl unit have tended to become non-operational at high wind speeds due to the creation of turbulence within the cowl, and that this tendency can be avoided by creating the venturi effect in a zone surrounding the stream of chimney gases instead of, as in the known designs, within said stream.

The prior art designs also tend to create substantial obstruction to the existing chimney gases, which may possibly also have contributed to the tendency to turbulence. In a preferred arrangement in accordance with the present invention, the chimney pipe has an on-axis support providing a bearing for an on-axis spindle forming part of the cowl assembly, and said support and the said spindle are mounted to the chimney pipe and cowl pipe respectively by radial arms affording a minimum of obstruction to passage of gases through said pipes.

A practical arrangement of cowl unit in accordance with the invention is now described by way of example with reference to the accompanying drawings, in which: Figure 1 is an elevational view of the cowl unit; Figure 2 is a plan view thereof; and Figure 3 is a cross-section on the line A-A of Figure 1.

In the drawings, the reference 10 denotes a pipe which attaches to a chimney 12 (see Figure 3). In the drawing, the chimney pipe 10 is shown fitting inside the chimney, but it could fit outside or it could be flanged to sit on the top lip of the chimney, with prongs or legs, possibly forked, extending down the inside and/or outside of the chimney. In any case, the chimney pipe 10 will fit and be secured in a rain-proof and substantially air tight manner to the chimney 12, jointing possibly being consolidated by a mastic compound, asbestos or other suitable material.

A bearing housing 14 is fixed on the generally vertical axis of the chimney pipe 10 by radial arms 16, which offer only minimal obstruction to passage of chimney gases.

The bearing housing 14 receives a spindle 1 8 supported on the axis of a cowl pipe 20 by analogous radial arms 22, which again offer minimal obstruction to gas flow. The cowl pipe 20 is thus able to turn on the vertical axis of the chimney pipe 10.

The cowl pipe 20 has an exit section 24 turned through 90 degrees, thereby to extend generally horizontally., In the drawings, the entrance section of the cowl pipe 20 is shown fitting outside the exit section of the chimney pipe 10 with a small clearance just sufficient to enable free rotation of said cowl pipe relative to the chimney pipe. A telescopic-type arrangement of this kind is preferred in order to provide a rain seal and avoid unwanted gas flow at this point to or from the atmosphere.

Fixedly mounted to the exit section 24 of the cowl pipe is a cowl, generally referenced 26, which has a relatively steep, inwardly tapered section 28 leading from its entrance, a choke or throat section 30 and a relatively shallow, outwardly tapered section 32 leading to its exit.

In use, wind air is drawn into the entrance of the cowl, accelerated to create a venturi effect in an annular zone surrounding the cowl pipe exit, and thence decelerated to the exit of the cowl, thus causing a partial vacuum or negative pressure zone at and ahead of the cowl pipe exit as seen by the chimney gases which are exiting from the cowl pipe inside said annular zone. It is to be noted that the cowl pipe exit is located just downstream of the venturi throat in the cowl.

In Figure 2, reference 34 denotes arrows indicating the 360 degres free rotational movement of the cowl assembly which is permitted by its pivotal mounting. In accordance with a conventional windsock effect, as indicated by reference 36, the cowl is thus enabled to align with the wind direction 38. The wind air creates a positive pressure zone at 40, and the abovementioned negative pressure zone at 42.

With the cowl unit as above described, chimney gases are efficiently drawn out of the chimney and down draughts are eliminated. Operational efficiency is maintained even in high winds.

In order to allow rain and melted snow to drain away, the underside of the cowl is preferably perforated with a series of small holes, as indicated at 44 in Figure 1.

It will be appreciated that various modifications of the above described arrangement are possible within the scope of the invention as defined by the

Claims (8)

appended claims. CLAIMS:

1. A chimney cowl unit comprising a chimney pipe adapted for attachment to a chimney to receive chimney gases, and a cowl assembly pivotally mounted to the chimney pipe freely to turn about the axis of the chimney pipe, said cowl assembly including a cowl pipe for receiving gases from the chimney pipe and a cowl mounted to said cowl pipe to surround the exit of the latter, the cowl being open to receive the wind and having a throat section for creating a venturi effect in the wind air in an annular zone surrounding the exit of the cowl pipe.

2. A cowl unit according to claim 1, wherein the cowl pipe is generally in the shape of an L.

3. A cowl unit according to claim 1 or claim 2, wherein the cowl has En inwardly tapering entrance section and an outwardly tapering exit section on opposite sides of the throat section, the entrance taper being steeper than the exit taper.

4. A cowl unit according tr claim 1 or 3, wherein the chimney pipe has an on-axis support providing a bearing for an on-axis spindle forming part of the coil assembly.

5. A cowl unit according to claim 4, wherein the said support and the said spindle are mounted to the chimney pipe and cowl pipe respectively by radial arms affording a minimum of obstruction to passage of gases through said pipes.

6. A cowl unit according to any of claims 1 to 5, in which the entrance end of the cowl pipe fits with small clearance around the outside of the exit end of the chimney pipe.

7. A cowl unit according to any of claims 1 to 6, having drainage holes in the underside wall of the cowi.

8. A chimney cowl unit substantially as hereinbefore described with reference to the accompanying drawings.