GB2235758A

GB2235758A - Flue gas extraction system

Info

Publication number: GB2235758A
Application number: GB8920002A
Authority: GB
Inventors: Kurt Petersen
Original assignee: Exhausto AS
Current assignee: Exhausto AS
Priority date: 1989-09-05
Filing date: 1989-09-05
Publication date: 1991-03-13
Also published as: IE903203A1; GB8920002D0

Abstract

An extraction system for extracting flue gases from a gas fire includes a flue pipe 12 which, in use, is extended through a hole in a building wall and an extractor fan 18 mounted at the outer end of the flue pipe 12 within an extraction housing including a volute casing 10 for the fan. The flue pipe 12 is telescopic for adaptation to different wall thicknesses and comprises an insulating layer 64 between perforated inner sections (54, 56) and imperforate outer sections (50, 52). The fan 18, and a driving motor therefor, are mounted on a door 16 of the extraction housing, which may be opened for cleaning the interior of the housing and/or for servicing the fan.

Description

DESCRIPTION OF INVENTION Title: "Extraction system" THIS INVENTION relates to an extraction system for an appliance, such as a gas fire, producing noxious fumes or gases. More particularly, the invention relates to such an extraction system which is adapted to extract such gases or fumes through an opening in a vertical wall of a building.

It is an object of the present invention, in one aspect, to provide such an extraction system which is readily adaptable to different wall thicknesses.

According to one aspect of the invention there is provided an extraction system for extracting noxious gases or fumes from an installation, including a flue pipe adapted to extend through a building wall and an extractor fan mounted at one end of said flue pipe, wherein the flue pipe is telescopic to allow adjustment of the length thereof to suit different wall thicknesses.

It is another object of the invention, in another aspect thereof, to provide an extraction system which is more easily serviced than hitherto.

According to this aspect of the invention there is provided an extraction system for extracting noxious gases or fumes from an installation, including a flue pipe and an extraction housing at one end of the flue pipe accommodating an extraction fan, said fan being mounted on a hinged door forming part of one wall of the housing, and which door may be opened for cleaning the interior of said housing and/or servicing the fan.

Preferably the fan motor and said extraction housing are enclosed in an outer housing which also serves as a guard and is readily removable for access to the extraction fan and said door, the extraction fan is in the form of a centrifugal impeller or tangential blower and is arranged, in operation, to form a low-pressure region adjacent its rotary axis, at the end adjacent said door, and said door has a central aperture opening into said low-pressure region, and the impeller is carried by a shaft extending, from said motor on the outside of said door, through said central aperture with substantial clearance, the motor body being so mounted on said door as to allow a space for air flow from the interior of said outer housing through said central aperture to the said low-pressure region, and wherein the arrangement is such that when said outer housing is in place a predetermined leak or other passage is provided for the passage of ambient air into the interior of the outer housing to replace air drawn from the interior of said outer housing to said low-pressure zone within said extraction housing whereby, in operation, a flow of ambient air is provided around the motor of said extractor fan.

An embodiment of the invention is described below by way of example with reference to the accompanying drawings, wherein FIGURE 1 is a view in longitudinal section of an extraction arrangement embodying the invention, FIGURE 2 is an end view of the arrangement of Figure 1, with an outer housing or guard removed, showing a hinged door carrying the extractor fan and its motor, FIGURE 3 is a view in section along the line 3-3 in Figure 1, and FIGURE 4 is a half-axial section, fragmentary view of a flue pipe, forming part of the extraction arrangement.

Referring to the drawings, the extractor unit illustrated utilises a centrifugal or "tangential" extractor having a volute casing 10 having opposite parallel end walls between which a volute chamber (i.e. a scroll-like chamber) of conventional form is defined, the outer periphery of said chamber being defined by a peripheral wall extending between the opposing end walls. Secured to one of the end walls of the volute casing is a flue pipe 12. The casing 10 comprises a main part, e.g. of cast-metal, providing the end wall adjoining the flue pipe 12 and also providing said peripheral wall. The opposite end wall of the volute casing is provided by a generally rectangular plate 14, on which is hingedly mounted a rectangular door 16 which carries the impeller or fan of the extractor, (indicated at 18) and an electric driving motor 20 for the fan.

In the operative condition, in which the door 16 is closed, the rotary axis of the impeller 18 is coincident with the central axis of the cylindrical flue pipe 12. The opposite walls of the volute casing have each a central circular aperture concentric with the central axis of the flue 12 and the remainder of the assembly. The central aperture in the volute casing end wall from which the flue pipe 12 extends communicates with the interior of the flue pipe and an annular metal funnel or duct 22 mounted at the junction of the flue pipe 12 with the volute casing leads from the interior of the flue pipe 12 to the eye of the impeller 18. The opening defined by the casing 22 is spanned by two parallel chordally extending pitot tubes 24 which form part of a gas flow sensing arrangement described below.

As noted above, the impeller 18 and its motor 20 are mounted on the door 16 which is hingedly connected, along a hinge 28, to the plate 14, the casing of the motor 20 being secured to the door 16 and the motor shaft extending through the door 16 and having fixed thereto, on the opposite side of the door 16, (and thus within the volute chamber) the impeller 18. The door 16 overlies the circular aperture, indicated by broken lines at 30 in Figure 3, in the rectangular plate 14. The aperture 30 is of such a diameter as to allow the impeller 18 to clear the edge of this aperture when the door 16 is opened by swinging outwardly away from the volute casing.

Releasable fastening means are provided to secure the door 16 in its closed position, for example a screw-threaded stud mounted in the plate 14, extending, when the door 16 is closed, through an aligned hole in the door 16 and a wingnut 34 screwed onto the exposed end of the threaded stud.

The above-described arrangement makes it a very simple matter to withdraw the impeller 18 from the volute chamber for access either to the impeller or the interior of the volute chamber, for example for cleaning the latter or for servicing the pitot tubes 24.

Also mounted on the door 16 is a differential pressure transducer or switch 38 which is connected by flexible tubes 40, with the ends, outside the volute casing 10, of the pitot tubes 24. Each of the pitot tubes 24 is closed at one end and extends, at its other end, sealingly through the peripheral wall of the volute casing for connection to the differential pressure sensing means 38. Each of the pitot tubes 24 has, in known manner, a series of openings formed through the wall of the tube along one side of the tube, the openings of one pitot tube 24 facing away from the impeller 18 and along the flue pipe 12 and the openings of the other pitot tube facing away from the flue pipe 12 and towards the impeller 18 and the door 16.Accordingly, a flow of air or other gas through the flue pipe 12 and the volute casing will produce a corresponding pressure difference between the interiors of the two pitot tubes 24.

A rectangular mounting plate 44, somewhat larger than the plate 14, is interposed between the flue pipe 12 and the volute casing 10. In use, the unit is mounted with the flue pipe 12 extending through a circular aperture formed through the wall of the building with the plate 44 engaging the outside of the wall of the building and secured thereto to hold the assembly in place. The flue outlet of a gas fire or like appliance within the building is extended into the end of the flue pipe 12 on the inner side of the wall, i.e. the end remote from the volute casing 10, which, together with the motor 20 and impeller 18 is positioned on the outside of the building.

Referring to Figure 4, which is a half-axial section, fragmentary view of the flue pipe 12, to a larger scale as compared with Figure 1, the pipe tube comprises a telescopic generally cylindrical outer wall comprising a first generally cylindrical outer wall portion 50, a second generally cylindrical outer wall portion 52 which is of slightly smaller diameter so as to fit slidingly within one end of the portion 50, a first perforate generally cylindrical inner wall portion 54 concentric with the wall portion 50 and a second, perforated generally cylindrical inner wall portion 56 which is of slightly lesser diameter than the wall portion 54 so as to fit slidingly and telescopically within one end of the portion 54.The ends of the wall portions 50 and 54 nearest the volute housing are received within an annular channel member 58 having its base secured to the mounting plate 44 adjoining the volute casing, with the end of the wall portion 50 lying within and secured to an outer peripheral flange of the member 58 and the end of the wall portion 54 being disposed on the radially outer side of an inner annular flange of the member 58. Similarly, the end of the member 52 remote from the member 50 lies on the radially inner side of and is secured to an outer annular flange of an annular channel member 60 similar to the member 58 and the end of the member 56 remote from the member 54 lies on the radially outer side of an inner annular flange of the member 60.It will be appreciated that, in principle, the arrangement described allows the combination of the members 52, 60 and 56 to be moved longitudinally relative to the combination of the members 54, 50, 58, to adjust telescopically the length of the flue tube 12. The annular space defined between the imperforate outer wall members 50, 52 and the perforated inner wall members 54, 56 is filled with a suitable insulating medium 64, such as glass or mineral wool. The provision of the perforations in the inner wall members 54, 56 and of the glass wool also serves a silencing function.

A cable 66, shown only in Figure 4, connects the motor 20 and the differential pressure switch 38 with a power supply and control facility (not shown) within the building.

The cable 66 passes through an aperture in the plate 44, through an aperture in the annular channel member 58, and along a channel-section conduit 68 arranged within the annular space between the inner and outer walls of the flue pipe 12. The cable 66 emerges through an aperture in the flanged annular member 60 to the interior of the building.

The conduit 68 is disposed closely adjacent the outer wall of the flue pipe defined by members 50, 52, and extends longitudinally, parallel with the axis of the flue pipe 12.

In installing the extraction system, and before assembly of the flue pipe 12, the conduit 68 is cut to the appropriate length, corresponding substantially with the thickness of the wall through which the flue pipe 12 extends, the insulation 64 is cut to a corresponding length and the flue pipe thereafter assembled as illustrated in Figure 4.

The control facility (not shown) within the building is used to control the supply of gas to a gas fire or the like appliance connected with the flue pipe 12 by ensuring that a solenoid valve (not shown) interposed in the gas supply will only be opened if the extractor system is operating properly and will be automatically closed if it is not.Thus, if the differential pressure between the pitot tubes 24 is such as to indicate that there is an adequate current of air or exhaust gas passing from the interior of he building through the flue pipe 12 to the volute casing 10, then the solenoid valve will remain open, but if there is insufficient pressure difference between the pitot tube 24 or if the pressure differential should be reversed, indicating that a current of air is passing from the volute housing 10 through the flue pipe 12 to the interior of the building, the control circuitry will cause the solenoid valve to close, cutting off the gas supply to the appliance.

The control facility within the building also includes, of course, switch means whereby the impeller motor 20 may be switched off when not required.

The portion of the apparatus projecting on the outside of the building, namely the volute housing 10, impeller motor 20, differential pressure switch 38, etc. is covered by a combined guard and cover 70 in the form of a rectangular metal box open on one side to fit over the volute housing 13, motor 20, etc. The cover 70 has a base wall 72 which is of the same shape as the plate 14 and only slightly larger, so that the plate 14 is a close fit between the remaining four walls of the cover 70. The cover 70 is secured in place by fasteners passed through these remaining four walls into peripheral flanges 74 provided around all four sides of the plate 14. One of the last-mentioned walls of the cover 70 has an aperture 76 registering with the open end 77 of the volute casing 10 to allow passage of extracted fumes from the unit. Contrary to what is shown in the drawings, the unit is preferably installed so that the openings 76 and 77 are on the underside of the unit, to exclude rain and wind-borne debris as far as possible, but it will be apparent that the orientation adopted may be selected according to the needs of the particular installation.

The locations of the fasteners securing the cover 70 to the flanges 74 are selected that when the cover is so secured, the open end of the cover 70 is spaced slightly from the plate 44, leaving a gap through which cooling air may be drawn into the interior of the cover 70. The marginal portion of the plate 14 is also provided with holes permitting the passage of air.

The body of the motor 20 is secured to the door 16 through the intermediary of a plurality of spacers 80 and the impeller shaft extends from the motor body 20 to the impeller 18 through a circular aperture in the door 16 such that there is a substantial clearance between the edge of this aperture and the motor shaft. This aperture opens into the interior of the impeller 18, (which is supported from the motor shaft by way of an open "spider" (not shown)).

Accordingly, when the unit is in operation, air is drawn from the interior of the housing 70 past the spacers 80 and through the clearance between the motor shaft and the aperture in the door 16 to the lower-pressure space within the interior of the impeller 80, to be driven out through the volute in the same way as the exhaust gases drawn from the flue pipe 12. Fresh air passes into the interior of the cover 70 from the clearance between the open end of the cover 70 and the plate 44 and through the peripheral openings in the plate 14, so that a current of cooling air past the motor 20 is maintained during operation of the extractor.

Claims

CLAIMS:

1. An extraction system for extracting noxious gasses or fumes from an installation, including a flue pipe adapted to extend through a building wall and an extractor fan mounted at one end of said flue pipe, wherein the flue pipe is telescopic to allow adjustment of the length thereof to suit different wall thicknesses.

2. An extraction system for extracting noxious gases or fumes from an installation, including a flue pipe and an extraction housing at one end of the flue pipe accommodating an extraction fan, said fan being mounted on a hinged door forming part of one wall of the housing, and which door may be opened for cleaning the interior of said housing and/or servicing the fan.

3. An extraction system according to Claim 2 wherein the fan motor and said extraction housing are enclosed in an outer housing which also serves as a guard and is readily removable for access to the extraction fan and said door, the extraction fan is in the form of a centrifugal impeller or tangential blower and is arranged, in operation, to form a low-pressure region adjacent its rotary axis, at the end adjacent said door, and said door has a central aperture opening into said low-pressure region, and the impeller is carried by a shaft extending, from said motor on the outside of said door, through said central aperture with substantial clearance, the motor body being so mounted on-said door as to .allow a space for air flow from the interior of said outer housing through said central aperture to the said lowpressure region, and wherein the arrangement is such that when said outer housing is in place a predetermined leak or other passage is provided for the passage of ambient air into the interior of the outer housing to replace air drawn from the interior of said outer housing to said low-pressure zone within said extraction housing whereby, in operation, a flow of ambient air is provided around the motor of said extractor fan.

4. An extraction system substantially as hereinbefore described with reference to and as shown in the accompanying drawings.

5. Any novel feature or combination of features disclosed herein.