New• Mixing Valve
Page 28
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for Low-pressure Gas
The "G.M.and Mangoktsi Product Now Available
in Three Types. Device Fitted to Manchester Corporation Bus Gives Good Results
INDER pressure of fuel restrictions, Leiincreasing numbers of operators are employing conversions to various alternative forms of power. Among laundries, bakeries, dairies, mineralwater manufacturers and the like there are particular advantages in the use of low-pressure gas and to cater for this market Mr. G. A. Marigolet_si (Higher Road Works, Higher Road. Urmston, Manchester)has introduced a series' of gas-mixing valves.
G.M. carburetters, as they are called, are made in three models, NA, NB and NC, with respective prices of £3 15s., 25 and 28 5s. An adaptor to suit the induction pipes of individual engines is priced ,at 12s. fid. In all models the flow of gas-air mixture is controlled by a spring-loaded valve actuated antomatically by. manifold depression. As both air and gas come under this same control the proportions of the mixture remain constant at all throttle openings. Suitable adjustment is provided on the gas inlet itself, whilst the primary setting of the air is regulated by an adjustable disc. Once set both gas and air limits remain fixed.
When Model NA is chosen some provision has to he made for extra air supply when reverting to petrol. In the case of Model NB the carburetter includes a plug i.4)hich is quickly detached to achieve this purpose and is replaced when purely gas operation is desired. A safety blow-off valve which incorporates a flame-trap is a special feature of Model NC. • This valve takes the place of the plug and is partic:ularly valuable where big engines having large-capacity manifolds are being converted. The blow. o1 device operates through a springloaded valve which also serves to supply extra air for petrol running; it can be pegged open by dropping a split pin through a slot in the guide or can be worked, if desired, by a lever fixed in the cab, Where maximum performances are to be obtained this model is suitable for a choke up • to 28-mm. bore.
• Double Instrument for Buses • For still larger machines a double carburetter is recommended which has been developed for use on buses. This latest type, which has been put into service by Manchester Corporation, has " been designed as a result of earlier tests on this operator's vehicles. The main chamber houses two mixing valves with the safety blow-off device, whilst air is filtered,, provision being made for fitting air cleaner and silencer.
For use in this connection a Crossley single-deck bus had already received certain modifications, the compression ratio being reduced to approximately T9 to I and coil ignition being fitted in place of the injectors. Heavy-duty conditions necessitated the employment of a racing-type coil.
With the earlier type of G.M. double gas carburetter, working in the same manner, the machine was found to cover a mile under service conditions on 52 cubic ft. of gas. Either full-gas or full-petrol operation is possible or desired intermediate gradings. The double carburetter is fitted with positive change-over tap for turning from mixture to full petrol in the event of the bag being exhausted.
Normally the trial bus is operating an 81-mile route and carries 700 cubic ft., but larger sizes. are to be introduced in the near future. Refilling chn take place at the terminus standpipe and the complete filling occupies approximately four minutes when a 3-in. pipe is in use. Eight additional buses are shortly to be equipped and it is likely that they will operate as supplementary vehicles during rusi, hours on the Manchester circular sub. urban service.