I believe that the metal box to be found on the external nearside of petrol-engined buses was called an AUTOVAC. If so, what did this piece of equipment actually do? I can find no mention of the device on the web.
Chris Hebbron
15/11/11 – 11:09
The AUTOVAC is a fuel lifting and supply device, which works from a vacuum source from either an operational petrol or diesel engine. The AUTOVAC is mounted on a bulkhead higher than the float chamber of a carburettor of a petrol engine or the injector box for a diesel engine. Fuel in the AUTOVAC flows by gravity to these devices. AEC, Bristol, Crossley, Daimler, Guy and Leyland all used the AUTOVAC fuel system in the thirties but gradually changed to using the fuel pump before 1940. Bristol, however, was the only Company to continue using the AUTOVAC until 1950 when their KS and LL models appeared.
Richard Fieldhouse
15/11/11 – 11:12
All the info you need here Chris including a service manual http://autovac.derekharris.com/
Spencer
16/11/11 – 07:06
As stated by others, the Autovac is basically a vacuum operated fuel pump that was fitted to many buses, commercial vehicles and cars in pre war days. With a petrol engined vehicle the vacuum could be sourced from the inlet manifold but with a diesel engine it must be sourced from an exhauster. The main advantage of an Autovac is that a ready supply of fuel is available to the engine when starting from cold as it is fed by gravity to either the carburettor or injection pump. This does assume that the fuel tap has been turned off after the vehicle was last used, and turned on again before starting!
John Barringer
16/11/11 – 07:12
An old retired Yorkshire Woollen conductor once told me that a driver he knew used to wait until they were out in the sticks and he used to fill two stone bottles from the autovac and he ran his motorbike on it.
Philip Carlton
16/11/11 – 07:13
Thanks Richard/Spencer, for the information. The diagram in the link was useful in showing how it worked. Compared with a fuel pump, it is complicated and poses the question of why pumps hadn’t been used earlier than the late ‘thirties. As ever, an answer often provokes more questions!
Chris Hebbron
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