An electric pump has a similar diaphragm-and-valve arrangement, but instead of the camshaft, a
) provides the pull on the diaphragm.
The solenoid attracts an iron rod that pulls the diaphragm down, drawing petrol into the chamber.
At the end of its travel the iron rod forces apart a set of contacts, breaking the current to the
and relaxing the pull on the diaphragm.
When the diaphragm return spring raises the diaphragm, it also pulls the rod away from the contacts; they then close so that the solenoid pulls the rod and diaphragm down again.
Circulating petrol continuously
Most mechanical and electrical systems pump fuel only when the carburettor needs it. An alternative system has a complete
of pipes, from the tank to the carburettor and back again. The pump sends petrol continuously round this circuit, from which the carburettor draws petrol as it needs it.
Filtering petrol and air
Both petrol and air are filtered before passing into the carburettor.
The petrol filter may be a replaceable paper one inside a plastic housing in the
. A pump may include a wire or plastic gauze filter, and sometimes a bowl to catch
is a box fitted over the carburettor air intake, usually containing a replaceable paper-filter
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resembles the simpler variable-jet type (See
How variable-jet carburettors work
) in having a
- a constricted neck - through which air flows on its way to the
The purpose of the
system is to generate a very high
age from the car's 12 volt
, and to send this to each sparkplug in turn, igniting the fuel-air mixture in the