Petrol Pumps TTF1.0
What it does
It is an electric motor driven unit that draws fuel
from the fuel tank and delivers it, at high pressure,
to the fuel injection system via the fuel filter.
How it works:
Two different types are commonly encountered; the
under-car type and the in-tank type.
The under-car or in-line type, as its name suggests
sits under the car in the general area of the fuel
tank. Gravity supplies it the fuel from the tank.
The pump assembly consists of a 12v motor which drives
a pump assembly; the pump assembly is usually either
a “roller cell” or “gear”
type pump, which creates a positive output pressure.
The pressure depends upon manufacture. A one-way valve
is usually incorporated into the outlet of the pump
to prevent fuel flowing back into the pump with the
ignition turned off; this helps to prevent the formation
of vapour bubbles.
Note:
Some manufacturers utilise an under-car pump that
fits into a small swirl tank which also fits under
the car, this is fed by a small, low-pressure, in-tank
pump; Volkswagen, SAAB, Audi and Volvo are the most
common manufacturers to use this layout.
In tank pumps have recently become the norm. The
pump is totally submerged in the fuel tank; it is
often part of an in-tank assembly which combines the
fuel level gauge sender unit, a swirl pot, a one-way
valve and the pump into one assembly. The pump itself
comprises of a small 12 volt motor which drives the
pump element which is usually of a sliding vane type.
There will be a coarse primary filter fitted to the
bottom of the pump in the form of a plastic strainer
“sock”. Some in-tank assemblies incorporate
a
“sucking jet” assembly which ensures that
the fuel pump is kept submerged during conditions
such as cornering or accelerating.
This type of pump can be replaced either as a complete
assembly with sender unit etc or as a pump only, in
this case, the assembly is stripped, a new pump fitted
and then the unit is reassembled. The second option
usually has the advantage of being a little cheaper,
but more work is involved fitting it.
Caution:
With either type of pump, the fuel flowing through
it is used as a lubricant. Without fuel flowing, when
it runs dry or suffers a fuel shortage, the pump it
will have no lubricant and hence damage will occur.
Reasons for failure/testing:
The single biggest cause of failure is due to the
ingress of dirt/foreign bodies into the pump. The
initial source of debris can be the fuel itself due
to refining failure, from the filling station tanks,
degradation of the vehicle’s tank lining, ingress
from poorly fitting fuel pipes, dirt being allowed
in during servicing such as when renewing the fuel
filter.
It is important to check for the source of the dirt
ingress and fully clean the fuel tank, fuel lines
and renew the in-line filter BEFORE fitting the replacement
pump or damage to the new pump will occur.
For further technical information concerning Petrol
Pumps please phone our technical help line or visit
www.fpuk.co.uk
