<VV> Healthy pumps?

[Kenneth E Pepke]

As the eccentric rotates it pushes up the pump diaphragm against 
the spring creating a low pressure area in the pump chamber. 
The atmospheric pressure in the gas tank pushes gas along the
gas line and pushes the internal valves off their seats to fill the low 
pressure area.   Once the carb is full the float / needle seat stops the 
flow of gas against the pressure of the pump spring.  At that point the 
inlet valve in the pump is being held closed by the pressure created 
by the spring so the gas does not flow back towards the tank.  This 
effectively 'hydraulics' or stalls the pump so the diaphragm / spring is 
not able to push the pump pushrod back down to meet the eccentric 
at its low position.  The eccentric continues to move its pushrod up 
and down but the pump pushrod is suspended at the highest point 
of the travel.  The diaphragm is stalled so no gas is moving ... the 
SPRING continues to apply pressure to the gas in the pump chamber 
until the float in the carb allows more gas to flow.

The needle seat works sort of like a person putting their finger over
the end of a hose to stop the water flow.  The flow can be stopped if
the line pressure is low enough.  When the pressure is too high the
water will force itself by your finger and spray all over.  In the same 
manner too much spring pressure in the pump will force the needle 
of the seat and raise the level of gas in the carb chamber until it 
overflows causing poor engine operation.
Ken P

On Thu, 17 Jul 2008 13:45:19 -0700 corvairs <corvairs at pacifier.com>
writes:
> Ron - If the valves do not allow "cycling" then the system could 
> continue to build up pressure until you had a failure. The pumps are 
> 
> designed to "cycle" (that is re-circulate gas without pumping out) 
> when 
> excessive pressure is obtained. Now, we DO know that a return line 
> was 
> offered on mid 63-66 turbos because, when under boost, it was 
> possible 
> to essentially "overcome" the pumps intended design. (Keep in mind 
> that 
> the turbo carb has one little float rather than 2) But none of these 
> 
> factors have ANYTHING to do with the internal spring in the pump. 
> That 
> spring exists solely for the purpose of making sure that the pump 
> diaphram  follows the crankshaft eccentric. It has NOTHING to do 
> with 
> the pressure the pump puts out.       Lon
> 
> www.corvairunderground.com
> 
> 
> Ron wrote:
> > The float valves turn the flow on and off.  The fuel pump provides 
> a design 
> > pressure whether it's on or off.
> > RonH
> >
> > ----- Original Message ----- 
> > From: "corvairs" <corvairs at pacifier.com>
> > To: "Jack Kean" <jkean at sbcglobal.net>
> > Cc: <virtualvairs at corvair.org>; "Frank DuVal" 
> <corvairduval at cox.net>
> > Sent: Thursday, July 17, 2008 1:17 PM
> > Subject: Re: <VV> Healthy pumps?
> >
> >
> >   
> >> Jack - This current hysteria about fuel pump pressure is an 
> internet red
> >> herring.  Mechanical pumps have put out that kind of pressure all 
> along.
> >> (or at least, it is within range). Are you having problems that 
> have
> >> lead you to look at pump pressure?  By the way (to you guys who 
> said
> >> that the valves don't regulate the flow of fuel under pressure) 
> how then
> >> does the stock Corvair system "shut itself off" (stop fuel flow) 
> when
> >> the carb bowls are full or when the secondaries are closed?    
> Lon
> >>
> >>
> >> www.corvairunderground.com
> >>
> >>
> >> Jack Kean wrote:
> >>     
> >>> I inserted a fuel pressure gauge in the fuel line, in place of 
> one of
> >>> the secondaries in my 140 hp yesterday. It was registering 
> around 8
> >>> pounds at idle, 9 pounds per square inch off idle. Seems at 
> least double
> >>> the numbers listed in the shop manual. I am not sure of the 
> source of
> >>> this mechanical pump, since it was on the car when I purchased 
> it. I
> >>> will be looking into a fuel pressure regulator, which I will be 
> able to
> >>> continue to use if I chose to change to an electric fuel pump.
> >>>
> >>> jack kean
> >>>
> >>>
> >>>       
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> >>     
> >
> >
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