>Hi Folks,
>
> Hate to disprove the theory that an inline filter BEFORE the fuel
>pump destroys the diaphragm in the pump, but I have been running this
>way for years and not a problem. I am running the original type of
>mechanical pump as fitted to the Sunbeam Talbot "Proper" Alpines.
>FWIW.
>
>Bob
Well.... There is a little to the original statement.
I felt a little tempted to clarify when and why the filter before the pump would be a problem, but the statement was more true than not, so I left it alone.
The bottom line is that if the filter has a low pressure drop, and is not clogged, then a filter before the pump is OK. If one of the two conditions is not true, then you can have serious problems, and the pump will die an early death.
Heres why.
Mechanical fuel pumps use an eccentric to pull directly on the diaphragm of the pump, which draws in fuel through a one way valve into the pump chamber. After the eccentric begins to release the diaphragm, the pumps spring puts pressure on the diaphragm, and the actual pumping occurs.
The spring protects the diaphragm from the fuel pressure, by limiting the max amount of pressure that the fuel can be compressed to, but the negative pressure experienced by the diaphragm during the draw has no force limit, and the flexible diaphragm has to take up the force, by deforming "like the spring does" in order to allow the pump to fully stroke with a small or no change in chamber volume.
This causes the diaphragm to flex "friction", and if the restriction is high enough, will lead to an early failure of the pump as described before.
Jarrid Gross