[Healeys] Why carry spares

[rwil at sbcglobal.net]

Could it possibly be time for some physical measurements on a test
setup to see: what output pressure with two pumps in series, both 2 SU
and 1SU and 1Facet (or similar), and in parallel? and what happens
when one of the pumps in series packs it in?

>From reports here it looks as if SU pumps are pretty patient with all
possible setups.

-Roland
On Wed, 19 Mar 2014 16:01:59 +0000 (UTC), you wrote:

>OK, I'm not a theoretical physicist, and don't play one on TV, and we're not
talking electronics so I don't see how running two pumps in series doubles the
output pressure. AFAIK, the output pressure of an SU pump is determined by the
strength of the spring that pushes the diaphragm (presuming the solenoid is
strong enough to compress an even stronger spring). There may be some internal
'regulation'--there is a small hole between the input and output chambers on
BN1/2 pumps that may provide a pressure limit by bypass--but no real pressure
regulation. So, if the spring is capable of producing, say, 3PSI when the
solenoid is switched off, then the output to the second pump will, at most,
push the spring back some but it wouldn't add to the 3PSI.
>
>IOW, a spring capable of pushing a diaphragm at 3PSI won't be able to push at
6PSI, just because the incoming pressure is greater. Anyone actually measured
the pressure of two SUs in series?
>
>Bob
>
>----- Original Message -----
>
>
>
>Two pumps in series might not be suitable for a racing Healey, but they have
>worked just fine on my street BJ8 without any problems for a long time.
>It's just simpler to plumb them in series than in parallel, in my opinion.
>If you have two pumps in parallel with separate switches, then you can run
>both pumps at the same time and get twice the flow rate at the same output
>pressure. Running two pumps in series at the same time will provide the
>same flow at double the output pressure - not good for the carbs. So, for
>pumps in series there should be only one switch to prevent running both
>pumps at the same time.
>
>
>
>Steve Byers