Hi Leon;
I'm a little late responding as I spent
the weekend rebuilding my dirt bike with one of them ole fashioned piston
engines what go up & down to make something go round 'n round? What a
goofy idea!
Anyways, back to the subject at hand.
Pressure recovery ?... so what? Well without pressure differential there
is no flow. None. I realize that jets are used to meter flow and that a
restriction is an impediment to flow, however my point was that if the EFI
pump has an outlet of say 1/8" into a 3/8" line (or in Bob's case, his 1/4"
return line) it does not have the equivalent flow of a 1/8" line. While
it will not have full flow of an unrestricted line due to permanent
pressure loss, it will recover much of its pressure resulting in a much
greater flow than would be provided by a 1/8" tube. To calculate this the Beta
ratio of the "orifice" is required, however it really isn't that important.
Besides, I can't find right now the required formula. I should get back to
studying this as I return to school for 4th year in 2 months and I can be
assured that there will be at least one twisted question concerning this on
the incoming exam.
Someone had mentioned drilling out the
pump outlet to reduce this restriction, but that would be a really bad idea.
The pump outlet is usually sized smaller than the pipe that it is sized for in
order to provide adequate back pressure to the pump to prevent cavitation. If
you drill out this outlet, then bubbles can/will form in the impellor and the
resulting cavitation will result in less flow and quite possibly the vapour
lock that we are trying to avoid. This restriction does not diminish the
requirement for a proper sized tube to be plumbed to it in order to achieve
rated flow.
Just my 2 bits worth
Cheers
Todd
So I just can't see what the size of an
attached pipe has to do with the flow rate through a "vena contracta"
("vena constricta"??). You also say "but much of this pressure is
recovered downstream" Hmmmmmm, ... I say "so what"??. We aren't
interested in pressure drops or pressure recovery, ... it's flow rates
that are the SOLE issue, and the capacity of an open
flow 1/4 inch line to get rid of the fuel dumped by the
regulator.
Leon