C.A.V. Developments to Increase Engine Output
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UNLIKE many conferences, that held by C.A.V., Ltd., at Eastbourne, last week, for their southern area agents, was mainly devoted to business. In the technical discussion, which was opened by Mr. H. P. Astbury, director of sales engineering, Mr. J. C. H. Lovelock, M.I.Mech.E., joint diesel sales manager, said that the demand for the oil engine was such that production was being stepped up in this and other countries, hat Great Britain led the way in developing the high-speed type.
Progress with the small unit for private cars was slow, but it had proved a tremendous advantage for taxis and light vans. Practically all taxis delivered in London for the past two years had oil engines, and a large percentage of others had been converted.
To increase engine output, C.A.V. had introduced certain modifications and improvements without increasing the cost. The multi-cylinder "in " A-type pump now took elements up to 8 mm. diameter and was called the AA. It was produced in fouror six-cylinder versions. Interchangeable with its predecessor, it suited direct-injection engines up to L3 litres per cylinder.
The N-type multi-cylinder pump had become the NN, to cope with supercharged engines, and was suitable for those up to 2.5 litres per cylinder.
To obviate fuel leaks with higher pressures, a solid soft-steel washer had been introduced for the delivery-valve holder, and an oil-resisting Neoprene "0" ring to act as a low-pressure seal.
The pump-element-plunger helix was now a groove and not cut from the solid. This reduced the volume of fuel, facilitated machining and gave an improved delivery characteristic with less variation in deliveries.
Mechanical, pneumatic and hydraulic governors had been modified to meet special requirements, particularly in the tractor field. Choice was left to designers. If cost was vital, the pneu
matic type was favoured. It was cheaper and easier to maintain. Although not always ideal, the embodying of double pitot and air valve had made it suitable for certain roadvehicle applications, but it was susceptible to atmospheric conditions.
The two-speed mechanical governor was best for vehicle applications, and either the two-speed or all-speed hydraulic type proved satisfactory on road vehicles, but was more expensive. This was discounted by the reduced wear, in some cases hardly measurable after 400,000 miles.
Dustproofing of fuel pumps had received much attention, whilst fuel contamination was a major problem. Investigation showed that the most damaging abrasive particles were between six and 12 microns and these readily passed both cloth and felt filter elements. A new paper element, with 600 sq. in. area, had, however, proved excellent.