[Healeys] Why carry spares

[Bob Spidell]

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 

HBJ8L/36666 

BJ8 Registry 

AHCA Delegate at Large 

Havelock, NC USA