THE AIR CLEANER

Evening Post, Issue 2, 2 July 1932, Page 15

THE AIR CLEANER

PROFITABLE FITTING

FEWER ENGINE OVERHAULS

So far as major alterations to conventional lay-outs arc concerned, engine design has now reached practically a. stationary stage, and the factors influencing, the durability of the unit have received a larger share of attention than formerly. ,

The difference between a new quiet and efficient engine and an old noisy and inefficient engine is simply a matter'of wear. To prevent the depreciation, of the unit to the latter stage, obviously it is necessary to ensure that: the.petrol ; is mixed in the carburettor with clean air. It has become more and more realised by manufacturers and operators that a satisfactoiy means of cleaning or filteiiug the air entering the engine is imperative. This has lesulted in the fitting of various types of equipment specially designed to free the air of dust particles and abrasives.

Data are available- showing that an efficient air cleaner .will considerably reduce the wear of moving parts on an engine oven when running under the most favourable conditions of operation on city highwaya. The table below shows the results of tests carried out on two. now high-grade four-cylin-der truck engines of the same make and model, the engines being1 run for about 240 hours at'the normal governed speed and load, disassembled on completion of these tests, and measured accurately to ascertain-the, amount of wear' which has taken place.

niter. No Relative filter. wear. Inches. Inches. Cylinder walls 0.0011 O.OOStO 1.8 Pfstons: ' ...;;".. .....0.0005' 0:0036- ■ 1.7 Upper ring groove clearance .0.0110 0.0G50 1.6 Middle ~ ring . croovo clearance 0.0040 0.06C0 1,16 Lower ring Kroore clearance 0.0014 0 0230 1.16 Percentage of V Jiicom■•bustlblo . matter in carbon '. 6,5000 31,0000 1.5 From, the operator's point of view, the time occupied in complete overhauls is lost and eventually.' reflected on the debit side of the profit and loss account. Under the conditions encountered by tractors in rural areas on account of the dust and grit, and trucks operating in an atmosphere of coal dust, gravel, or sand, etc., the period between overhauls of the propelling unit is seriously decreased unless some device which separates the impurities from,the air belore they enter the carburettor air in-take-is fitted. Very little imagination is required to obtain a clear conception of the damage such impurities can wreak on the cylinders, of the abrasive action of this dust and grit working in the fine clearances of the valve guides, pistons, ring grooves, etc., resulting in wear fon-.'which, in most cases, the lubricating'oil is held to be at fault.

These impurities cling to the oil film on the cylinder walls and a proportion eventually finds its "vvay past the pistons and rings into the sump, mixes with the Rubricating oil, and is carried to thebearings, cylinder walls, etc., causing wholly unnecessary wear and forming a -vicious circle only broken when the unit is overhauled and tho lubricating oil drained off. The existence of such conditions inhibits any attempt to secure efficient performance and low running costs—the factors of-vital concern to thft operator—although the* effects of thoso conditions may to some extent be mitigated by the use of a lubricating oil refined in accordance with the most modern technique. Such an oil will retain its body under conditions of'stiess longer than "an oil of inferior quality, and. although ■ its 'initial cost may bo slightly greater, eventually jt gives better results —that is, lowing running costs. The necessity for decarbonising, more often than not, provides the reason for the overhaul, and, if by the fitting, of an air cleaner.and the use of a lubricating oil of the correct body and character, carefully chosen iii accordance with the thermal and mechanical characteristics of the unit/this can be postponed and operating costs are coircspbndingly reduced. ADVANTAGES AND TYPES. An investigation conducted sonic time ago by the Society of Automotive Engineers' in. America elucidated that the overhaul period had been, further extended by tho use of the air cleaner than by any other accessory, the extension of tho period aud decrease in maintenance expenses for specific commercial fleets varying between 20 per cent, and' 50- per cent., variations being duo to differences in geographical and climatic conditions. The typo, of air cleaiier to be efficiently used in any particular application can only be determined after a survey has been mado of actual geographical, geological, and topographical features of the locality in which the unit will be chiefly operating. The chief points to bo considered in choosing an a,ir cleaner arc:—(l) Maximum efficiency to separate from the air the dust particles held in suspension; (2) minimum resistance to the flow of air; (3) accessibility for cleaning and repair; (4) minimum amount of attention; (5) compactness, light, weight, and relatively, few moving paTts. Of, these the most important, perhaps, are the first and second, since both, directly affect the maximum power developed by tho unit. The types of air -cleaners now marketed may be broadly divided into threo main classes, within tho boundaries of which there may bo an almost