THE VENTILATION OF MOTORBUS BODIES.
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The Ideal System of Changing the Air in a Bus Interior and the Different Methods that are Employed to that End.
TENTILATION is of particular importance in a V multi-seated vehicle which has the seats placed closely together, and in which the headroom is no greater than is necessary for the average person to stand up in. A constant supply of fresh air has to be provided, the impure atmosphere carried away and any heat or odour from the engine excluded. The ideal
system should operate Without draughts, and be so designed that its Successful working it not materially affected by the weather conditions..
Ventilation at the Roof Level.
As respired air is heated it tends to rise; therefore, the easiest way of getting rid of it is to provide an outlet at the roof level. It is not difficult to do this in a single-decker, and there is the advantage that all the ventilation required can be effected above the heads of the seated passengers so as to be practically unnoticeable. The average amount of air space per passenger in a single-decker, or the lower saloon of a double-decker, does not exceed 25 cubic ft. This contrasts strongly with 600 cubic ft. per head, which is considered very moderate for the room of a dwellinghouse. The bus, however, is a moving object, and the greater the speed the sooner can the air be changed inside.
Scuttle-dash Ventilation.
Good use is made of the exhaust if it be led through piping for heating the bus on a cold day ; lout, if not properly under control, it can be the source of considerable discomfort in any weather. Any heated air arising from the engine must be excluded for similar reasons. The best way of dealing with this hot air is to provide good ventilation as near as possible to its source of supply. The success of any such scheme depends to a large extent on the general design of the front of the vehicle. If there be a scuttle panel between the dashboard and windscreen, then a movable panel in the top of the scuttle is more effective than ventilalors let into the sides of the scuttle. The top ventilator should be at least 18 ins. by 6 ins., or of equivalent area, and have a baffle Plate inside so as to direct the stream of air downwards. The side-scuttle ventilators are not so useful, because, apart from their size, fresh air does not accumulate in their proximity as it does naturally at the base of the windscreen. Wire gauze is often fitted behind these ventilators; but, although much dust and dirt are thereby excluded, there is the drawback that the rate of flow of air is reduced considerably.
The hot air is soon swept away if there be no door to the entrance to the driving seat, at least on one side; but even a half door—that is, one reaching to the waistline only—will tend to prevent cooling of the air if the scuttle be not well ventilated.
Modern bus design tends to complicate this problem. If the body be built right up to the radiator, it is necessary that there should be one or a pair of effective air extractors in the forward part of the roof, and any side-ventilating frames provided above the first two or three main windows should act as air outlets rather than inlets. Air rushes into the vehicle if an opening be provided more or less broadside on to its running as across the front, whilst air is drawn out through an opening if, an outside current of greater force be passing it more or _less parallel with the plane of the aperture. The amount of air extracted depends on the nature of any air currents already set up inside the bus, the size and position of the opening, the design and number of any other openings provided, and, of course, the speed of the vehicle and direction of the wind. If one of the main side windows be lowered it will usually act as a combined inlet and outlet ; the larger it is the more likely it is to perform the firstmentioned function. A sliding side window will often act more as an extractor than as an air inlet.
The Side Ventilators.
The hinged and glazed frames which are often pro. vided above the main windows form one of the most useful means of ventilating almost any kind of bus body. It is convenient to hinge them inwards from the bottom edge, because by so doing the overall width of the body is not increased when they are open. If there be a strong current of air rushing in -at the front just below the roof level, this will drive out some of the vitiated air although the ventilators. The outside air currents will assist this. operation, whilst at the same time some of the fresh air will enter. These ventilating frames act in a more definite manner if they be 'pivoted to open vertically. If, for instance, there be six of these frames along the side of the body, the first three may be mounted so as to hinge on their forward
edges, whilst the other three are hinged on their rear edges. The first three then operate as extractors, because the outside air currents are deflected along the face of the open ventilating frame, and, in rushing past the opening at the end, draw the air from inside the body and, as the main current is deflected outwards, only a small amount of air enters. The action is improved if there be only a rear opening and the space between the top and bottom edges and the side of the body be closed in This is easier to arrange if the ventilator be fixed and not hinged. When hinged, the range of movement must be limited to the overall limit which is imposed, and, if the sides of the body slope inwards from the waist to the roof, this contraction gives a corresponding extra amount of opening for the ventilators The three rear ventilators opening from their back edge act as scoops to trap the fresh air rushing along the sides of the body. Here, again, if the top and bottom edges be free, the action of the ventilator loses part of its effectiveness as an inlet, because some of the air currents will flow under and over the open frame, giving an extractor action. Some builders prefer to transpose these two sets of frames and place the inlet forward and the extractors at the rear ; but, as a rule, extraction is of more value forward, because here the hot air and odour from the engine first accumulate.
Forward Control and Ventilation.
If the chassis has forward control the driver is often enclosed in a cabin on the off side of the bonnet. If totally enclosed, this cabin should be well ventilated, as there is less chance for the heated air to disperse than in a driving compartment which is the full width of the body. There should be effective air extractors both in the skle and roof, and it is an advantage if there be no door at the special driver's entrance, but an opening only. With this type of body the front bulkhead is built right up to the dashboard, and should be provided with plenty of air inlets. The off side is partly obstructed by the driver's cabin, but on the near side there is a free passage for the air above the top of the bonnet.
The space above the front ventilating rail should be generously provided with ventilators. The top front rail immediately under the roof may be pierced with louvres, and just below are three or four hinged frames opening inwards. These have side guards, so as to prevent the incoming air from rushing downwards and to ensure it being deflected upwards, so as to prevent, as far as possible, discomfort to the passengers, especially those on the front seats; but there is always the chance that, if the incoming air be deflected upwards at a sharp angle, some of it will descend again in the form of a rather unpleasant draught. This can be obviated to a great extent by the use of fairly large permanent openings in the middle of the front top rail. In order that the off-side portion of the bulkhead shall be as well ventilated as the other, there must be a free passage for air currents right through the upper part
B38 of the drivel's cabin. if the driver's windscreen does not reach to the canopy line, the space between this and the top of the screen should be provided with louvres. The air which rushes in, when the upper half of the screen is open, is deflected upwards to the underside of the roof. These air currents will increase the flow of air entering above the screen. If there be no opening at the back of the driver these air currents are deflected downwards and cause back draughts; but if there be an opening behind they are diverted into the saloon. A lorry cabin' is often defective from this point of view, and would be improved by the simple expedient of omitting the glass from the back lights.
Front Bulkhead Ventilation.
With the conventional type of steering position the front bulkhead may be continued right across the body or pierced for an entrance. Either design should have the entire upper portion above the ventilating rail provided with ventilators. Instead of opening all these bulkhead ventilators by hinging them on the bottom edge, a variation maybe made by hinging the side ones on their inner edges and the middle one only in the conventional manner. Then the side frames act as deflectors, diverting the fresh air along the sides and pushing out the foul air. This action is assisted by the outside currents flowing along the side of the body. The middle ventilator acts as an inlet only, and impels the heated air remaining towards the back and need not have any hinged flap, but instead be fitted up as a pivoted or sliding window. If there be a door in the bulkhead, this should be ventilated so far as compact construction allows by means of louvres, a hit-and-miss panel, or a neat sliding-glass panel working in a velvetlined metal channel in the upper part.
This door, however, is often omitted because one or a pair of doors is mounted at the top or bottom of the steps of a front-entrance bus. Here, again, the top part of the doors should be utilized as part of the scheme of ventilation. Being at the side of the vehicle, the openings provided act princiyally as air extractors.
The Importance of a Well-fitting Floor.
Before dealing with any further items of the ventilation, a few comments will be made concerning the exclusion of odours by means of a well-fitted floor. This requires good workmanship and reliable material, because provision has to be made for pedal slots, apertures for the working of control levers, as well as trapdoors to the gearbox and differential, whilst the clips which hold the body down on to the chassis are brought through the floor. The use of leather with slits in it fastened underneath has been suggested as a means of making the pedal-travel gas-tight. The slots in the footboards can be prevented from getting larger by covering them with aluminium matting cut away as neces sary. These front boards of the floor are seldom screwed (lawn, but it would be a decided improvement if they were. Under normal conditions these boards are only lifted in the garage, and very little extra time would be expended if, say, half a dozen metal-thread screws had to be unfastened. The advantage of using metal-thread screws for any of the floorboards which have to hi periodically taken up is that they can be taken out and replaced continually without injury. The edges of the boards would require metal ends or a tapped plate with a corresponding bearing of a similar nature on the bottom frame. The floorboards themselves should be of hardwood rather than cut from deals and made up, where necessary, with framed ends and battens so as to ensure that their original shape is maintained.
The Drop Side Windows.
The side ventilation of a modern single-deck bus body usually consists of all, or the greater majority of, the main windows being arranged to drop, with or without the adjustable ventilating lights above them, as already described. Smaller windows at the end of a driving Seat and between a front entrance and the front bulkhead or windshield, according to the position of the entrance, are seldom made adjustable. The glazed portions of doors are usually, fixed, whilst the small wihdowa at the ends of a back seat which is the full width of the body are also fixed, as a rule. The window which is directly over a deep wheel arch is often fixed, because it is not thought worth while providing a short drop, or hinging over the top half, or making a double run so that as large an opening is possible as with the other windows.
These side drop windows form a very attractive feature, and have done much to popularize the bus with the riding public; but the ventilation of any bus is inadequate if it depend chiefly on these side windows for the effective displacement of the vitiated air and the supply of fresh air, for on a very wet or cold day it should be possible to keep these windows closed without causing any undue discomfort. These windows should be regarded as a ready means of adding to the pleasure of travelling on a fine day, and if they be adjusted with intelligence it is possible to travel inside a bus on a hot and sultry day, and even over a dusty road, with more comfort than is possible in an ordinary open coach.
Roof Ventilators.
Sometimes the ventilating lights are omitted. This is done to simplify the construction. The windows are not increased in height, but, instead, the waist-line is kept fairly high and the roof well domed so that the cant rail is brought relatively low. This arrangement is satisfactory so long as there 4s plenty of area of air inlet in front and outlet at the back with three to six of the best type of air extractors in the roof, the number varying according to the size of the bus and the number of cross-partitions.
These extractors work on the same principle as has always been described with the vertically hinged side ventilators. Usually, the stream of air which rushes along the surface of the roof passes across a transversely arranged duct so as to pull the heated air from inside, or it may be diverted by baffles past these orifices or be made to set up a partial vacuum having a similar effect.
The Necessity for Well-fitting Windows.
Any window or ventilating light made to open and adjust must fit tightly into its rebate when closed. Nothing is so annoying as a concentrated stream of air issuing from a badly fitted window. The up-to-date window winding or balancing mechanism or just a simple catch should not be a source of rattling if it has been properly fitted. In fact, one might almost go so far as to say that a fixed window often sets up more noise than a drop or sliding one, because its unpolished edges have the chance, if not accurately fitted, of sawing through the rubber packing in course of time until the window works loose.
Ventilation at the Back.
At the back of the bus another factor has to be borne in wind which does not affect the front or the greater part of the sides of the body. This is the vacuum created at the rear by the displacement of the air as the vehicle is driven along. If there are any open windows or doorway at the back, the air from outside will tend to rush in; but it is oppoped by the rush of air along the roof and sides, and, if there be effective rear ventilation; by the stream of air from the underside of the roof. The force of this current is more or less reduced by the amount of air extraction taking place along the sides and roof. Again, the force of air rushing in from the back is strongest at abo.it the chassis level. The resultant effect, however, is strong enough to raise any dust which may be present if the vehicle be travelling fast. It will be seen also that there is a further advantage in utilizing the sideventilating frames towards the rear, as air inlets so as to combat, so far as possible, the air currents drawn in at the back.
The Tropical Bus.
The fact that the sides of the body above the waist are almost entirely of glass is the reason why the interior can be very stuffy on a hot day with the sun shining direct on the glass. By lowering the windows this source of discomfort is reduced, even if the window does not entirely disappear. The sliding window has not the same advantage, but the layer of air which is sandwiched between the halves of the window, when open, has a distinct value, because it is a bad conductor of heat.
Blinds are not often fitted in service vehicles, but are used, in many of the private hire type. The blind, If it is to be used as an effective shield from the sun, should be drawn after the window has been lowered. Buses for use in tropical climates are provided with jalousies or louvre panels made up in frames, in addition to the drop windows, a double run being required in the pillars. Another item adopted for buses for this class of work is the double roof. By this means a layer of air is introduced between the top and bottom roof boards, and, acting as an insulator, prevents the full force of the sun rays on the top of the roof from having effect on the interior of the vehicle.