<VV> Suction pumps vs pushing pumps

Tue Oct 5 11:58:05 EDT 2010

John gives a good description of the properties of pressure. Its the same as
lift on an aircraft wing. The wing is designed to force air over the top
skin faster than air goes across the bottom skin. In so doing, a low
pressure area is developed on top of the wing and the aircraft is literally
pushed up or kept level through a balance of the "pressure" on the bottom of
the wing and the "suction" on the top which is in the airplanes case, in
opposition to and balances out the forces of gravity.

A diaphram pump applies a suction or "vacuum" to the line wherever it is
located in the system, a higher pressure that goes in the vent of the tank
pushes on the fuel in the tank to the pump and the pump then with the use of
check valves, maintains pressure to the carburator.

A different type pump may require priming, because all it will do is spin in
the air within it because its internal clearance requirements, it needs a
more viscous fluid, like fuel, to pump, where a diaphram pump applies a
vacuum to the line, pulling fuel to it and with the use of the diaphram,
applies a pressure to the outlet, to the carbs..

regards  Mark Durham

On Mon, Oct 4, 2010 at 2:43 PM, <jvhroberts at aol.com> wrote:

>
>  Well said, Frank! One of the greatest frustrations in my professional
> career was explaining to engineers (who should know better!) how vacuum
> works. Nothing actually 'sucks' on anything. In a perfect vacuum, suction
> lift is impossible. Appreciate the challenges spacecraft engineers have on
> managing liquids in zero g and the absence of atmospheric pressure!
>
> Suction lift is defined by the ability of a pump to lower the pressure at
> the inlet relative to atmospheric pressure. For example, water can't be
> lifted more than 33 feet, and in practice, it's less than that because of
> the vapor that's generated under such low net suction pressures. Add flow
> resistance, and that number gets even lower once flow is established. Hence
> the reason wells have submersible pumps, jet pumps, etc.
>
>
>
> John Roberts
>
>
>
>
> -----Original Message-----
> From: corvairduval at cox.net <corvairduval at cox.net>
> To: virtualvairs at corvair.org
> Sent: Mon, Oct 4, 2010 5:34 pm
> Subject: Re: <VV> Suction pumps  vs pushing pumps
>
>
> Ned, you are wrong on several accounts. The first being that you think I
> said your pump can't work. Of course it does, I just mean it is not in the
> best location. I also don't think you need to change the location until a
> problem arises.
>
> The statement "the reason one pump can suck water from a greater depth is
> because it generates a greater pressure, ie is a more powerful pump" is
> wrong.
>
> A suction pump cannot be more powerful than the atmospheric pressure it is
> operating against. A bigger pump will just get more flow, not a higher suck
> point. The pump is just providing a vacuum, the atmosphere is providing the
> push. At 33 feet, you run out of push available from the atmosphere. A
> column of water 2.31 feet high is equivalent to 1 pound per square inch
> (PSI) of pressure. 14.7 psi (sea level standard pressure) taps out at
> 33.957 feet.
>
> Check out Suction Head section of this web site:
> http://www.ag.ndsu.edu/pubs/ageng/irrigate/ae1057w.htm
>
> I also guarentee the oil pump moving oil through pipelines are pressure
> pumps forcing the oil through the pipe, not sucking the oil from hundreds
> of miles away. Just like deep well pumps push the water up from hundreds of
> feet below the earth.
>
> I wondered why my oranges tasted like apples....   ggg
>
> Frank DuVal
>
>
> Original Message:
> -----------------
> From:  aeroned at aol.com
> Date: Mon, 04 Oct 2010 13:55:52 -0400
> To: virtualvairs at corvair.org
> Subject: Re: <VV> Electric fuel pump
>
>
>
> Really? Thanks for that tid bit....
> I guess it's a good thing no one told my electric powered rotary pump with
> no check valve that it can't do what it's doing, fortunately it's not on
> VV.
>
> Yup, you guys know more about fluid pumps, I surrender. Maybe I can get a
> refund on all the schoolin' that obviously weren't right.
>
> BTW the reason one pump can suck water from a greater depth is because it
> generates a greater pressure, ie is a more powerful pump. Obviously the
> pumps used to move oil in a long pipeline are not the same as an electric
> pump on a Corvair, but then again apples aren't oranges.
>
> Ned
>
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