VENTILATION SCHEMES
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for passenger vehicles
EFFICIENT ventilation is a characteristic of the modern public-service vehicle and the improvements which have been made in this direction have contributed largely to the popularity of the coach and motorbus. But those who specialize in the design and manufacture of adjustable windows are still striving to add . further refinements to existing types. Some new window mechanisms have recently been introduced and, in view of the experimedtal work now being conducted in various quarters, more may be expected in time for the Olympia Show next November.
The window that is receiving much attention at the present time is the half-drop pattern. It is easy to fit or to remove, if a glass be broken. It takes up no space below the waist rail and may be used above the largest of wheel-arches. It is usually made as a unit, that is, both fixed and sliding halves are combined in one assembly, otherwise the sliding frame is quickly put together with its side channels and the fixed frame added. The general design is compact and usually tire window requires no rebates in the pillars.
The half-drop window, is, as a rule, unbalanced, but it may also be obtained, like the full-drop windew, with a spring or springs to take the weight of the moving frame, which is an advantage in view of the wider lights now so often adopted. The window is released by means of a centre catch operating a rod in the top tube of the sliding frame. The locking mechanism may consist of a rack and pawl, or some variety of Wedge action. The importance of the length of contact of the wedge in order to ensure rigidity is fully recognized.
Rustless steel and non-corrodible alleys are freely used for the metal framework. Duralumin is also emplayed in order to reduce weight without sacrificing strength.
The design of the half-drop window has benefited by the improvements which have been made in the full-drop balanced variety. One has the choice between a control lever mounted on the garnish rail or, as in the case of the half-drop pattern, mounted on the top rail of the window itself. The garnish-rail control affords the opportunity for holding the glass tightly at the waist line and with a wide windowa retaining device in the middle is of value iu order to counteract the whip of the glass. This central contact, however, may also be obtained With top-rail control.
Another novelty in balancedwindow design is the elimination of any locking lever, thus simplifying the control of the window.
The winding mechanism which is so frequently standardized for the private ear is. made of more robust design for use on the public-service vehicle. The coachbuilder is left free to design the arrangement of his window channellings; and the mechanism is attached so that the. removal of the glass is facilitated. .
The mechanism which permits the window to be wound continuously is most in favour, because this does away with the necessity of having to reverse the direction of the handle after the limit of the'run has been reached. Detachable handles are supplied if the windows are to be under the care of the 'conductor.
Under the Conditions of Fitness Regulations it is stipulated that there shall be adequate ventilation without the need for opening the main windows. This order, however, does not come into force until after the end of this year.
This aspect of ventilation is no new problem, because such devices as are fitted may be regarded as the development of those which were essential before the introduction of the mechanically operated window.
The Regulations, however, do not specify that this part of the ventilating scheme shall operate when the main windows are open, therefore it is presumed that these ventilators may be either self-functioning, or require to be opened by hand.
The former type is to be preferred because it not only carries out the spirit rather than the letter of the law, but it also relieves the conductor of the task of adjustment.
When louvres have no sliding panels whereby the air currents may be entirely cut off they are selffunctioning. Such louvres should be inserted above the screen and at the top of any bulkhead, as well as in the back panel above the windows. By this means the vitiated air collecting under the roof is kept in motion and it is more easily driven out of the vehicle than when louvres are absent, or confined to one bulkhead.
The air extractor in the roof is a typical example of a modern ventilating device which works effectively when the windows are closed and the number of roof extractors may be reduced to a minimum when there are no obstructions to the movement
of the heated air _immediately under the roof.
Louvres, or a similar device, should be fitted above the screen of a fully enclosed driver's cab, because, under paragraph 41 of the Conditions of Fitness Regulations, such a compartment must be ventilated whoa the screen is closed. To be effective the opening above the screen should work in conjunction with a cabroof ventilator. This will also prevent downdraught when the screen is open.
Cant rail ventilation may be either temporary or permanent. An example of the former variety is the glass louvre fitted above the side windows. It is considered that in the near future this attractively designed accessory will be something more than a device acting as an cave or destination indicator when the windows are closed.
Ventilating frames, or small windows which are hinged and adjusted in various ways in order not to open beyond the legal limit of overall width, are not used so much as formerly, although, when made up as metal units, they are compact in design. They are useful as supplementary ventilators, particularly when mounted vertically so that they may function either as air inlets or outlets. Such frames are often mounted at the sides of the raised portion of a clerestory roof.
The provision of ventilators in the cant-rail itself, or in its panelling, is more in favour than previously, because the panel at this point forms an additional belt panel and thus helps to accentuate the length of the bus, and, therefore, detracts from its apparent height. This panel is also an important decorative feature, particularly of the doubledecker.
The cant-rail may have vertical or horizontal louvres cut in the metal panel, with or without an inside control panel, or the space behind the cant-rail may be enclosed so as to form a wind tunnel. When the overall width at the cant-rail allows, a separate ventilating device may be fastened outside it.
This ventilator may consist of a tube with internal baffles, or the air may flow over an external baffle, extraction of the air from the vehicle taking place by reason of the partial vacuum created behind the baffle.
Ventilation of the upper deck is effective so far as the main windows are concerned. Supplementary devices consist of louvres mounted in front, the overhanging canopy forming a useful means for controlling the incoming air currents. It may be pointed out that adequate ventilation is provided when the windows are closed, because there is no door at the top of the staircase and seldom one at the foot of it—even in the latest types of body.
Roof extractors need not add to the overall height of the bus because they can be inserted in the side camber of the roof. It is interesting to note that an additional ventilation facility is now provided in the shape of an opening roof—a refinement for the double-decker which has on more than one occasion been advocated in the columns of The Commercial Motor.