I did not think I was psychic until, not having thought about exhaust-pressure fuel-feed for many years, I mentioned that this was part of the originality of the 1903 Mercedes 60 Roger Collings used to own. Then a day later I read in the Crossley Register of how Charles Donovan has this system on his Shelsley-model Crossley and had cured its shortcomings, with much trouble and infinite patience.
This method of conveying petrol from rear tank to carburettor obviated either continual hand-pumping, a mechanical fuel pump or an Autovac when gravity would not serve with a low-hung petrol tank, and was used on some cars into the Edwardian age.
Mr Donovan’s interesting article reveals that using the exhaust gases to raise the petrol was no simple matter. Apart from a hand-pump to get the initial supply of fuel to the engine, the system involved a fire-avoiding Davy device, a non-return valve, a pressure-release valve, a pressure gauge, a filter with stopcock and a drain cock. These could combine to play up in most depressing ways. All credit, then, to Collings and Donovan for having their cars function so well with their original intestinal organs.
In the aforesaid article is the revelation that the 1908 Rolls-Royce sales catalogue announced the abandonment of exhaust pressure feed as “dirty, uncertain and otherwise objectionable”. It had been changed for “a small air pump”, with presumably a hand-pump for starting.
How honest, from the makers of ‘The Best Car in the World’! Apparently, on the famous 15,000-mile RAC-observed trial of a 40/50 ‘Silver Ghost’ in 1907, the valve had been cleaned 10 times, the petrol cap, filter and its tap or drain plug adjusted eight times, the hand feed-pump refixed four times, the exhaust pressure pipe repacked once, and a new tap and connections had been fitted. I am not sure if this was recorded in the official report? Sad, for owners of 1907/08 Ghosts.