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Dana
Joined: 13 Dec 2007
Posts: 1047
Location: Connecticut, USA
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 Posted: Tue Jan 19, 2010 3:23 pm Post subject: Bing54 / Max height btw Fuel tank and Mikuni fuel pump |
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At 05:50 PM 1/19/2010, LageB wrote:
| Quote: | May I understand you so, that in case "El.pump + Puls.pump" combination, the resulting pressure will be whichever pump's pressure is higher, actually regardless whether I connect in series or parallel?
If so, Rotax' choice of words are somewhat misleading when they say that pumps should be connected in parallel to avoid excessive pressure.... |
I could be wrong, just going on theory here, but the way I see the pressure from a pulse pump in series with an upstream electric pump is not additive. Here's how I see it, feel free to knock holes in the theory:
Fuel is drawn into the pulse pump chamber when crankcase vacuum pulls on the diaphragm and the inlet check valve opens, or the upstream electric pump pushes it in. When the piston moves down and creates crankcase pressure, that pressure is transmitted to the diaphragm and in turn to the fuel in the pump chamber, and only if it's greater than the electric pump pressure does the inlet check valve opens. At the point there is no connection to the fuel upstream of the pulse pump, so the only thing pushing fuel to the carburetor is the diaphragm... as if the electric pump didn't exist.
If the electric pump creates a greater pressure than the pulse pump can, the inlet check valve will never close at all, and the fuel pressure in the pump chamber will push back on the diaphragm so that it never moves, and it's as if the pulse pump didn't exist.
Either way, the pressures don't add.
The pulse pump doesn't create a differential pressure between intake and outlet; it creates first a vacuum, then an outlet pressure... not at the same time so they're not related. I'm familiar with the internal workings of a Facet pump, but if (like most electric rotary pumps) it creates a continuous differential pressure, then if you put the electric pump _downstream_ of the pulse pump, the pressures WILL add.
Yes, I know we're not talking directly about a Kolb here, but many of our Kolbs have an identical fuel system so I see it as "Kolb related."
-Dana
--
2000 mockingbirds = two kilomockingbirds [quote][b]
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LageB
Joined: 18 Jan 2010
Posts: 5
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| Posted: Wed Jan 20, 2010 3:02 am Post subject: Re: Bing54 / Max height btw Fuel tank and Mikuni fuel pump |
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| Dana wrote: |
If the electric pump creates a greater pressure than the pulse pump can, the inlet check valve will never close at all, and the fuel pressure in the pump chamber will push back on the diaphragm so that it never moves, and it's as if the pulse pump didn't exist.
Either way, the pressures don't add.
.... |
Dana, I am not quoting your complete explanations as above, I just want to say.. absolutely fabulous! I have vacuumed the net on Mikuni-El.Pump interaction phenomena, but I have never seen this explained before. It makes perfect sense to me. For many Rotax (& Kolb) users (incl Rotax themselves as seems?) it must be rather valuable information that pump pressures would not add in case of series connection. For example in my case, I was just about to select booster pump "just to help" the Mikuni - assuming pressures would be added. But, now I clearly understand that, if the original problem is too high lifting height, -then, it is vital that the electric Pump (intalled prior Mikuni) MUST have pressure sufficient, by itself, to cope with full requirement of the double Bings. Of course it is good thing for the redundancy as well. May I assume, also, that this fact eliminates need of pressure reducers, as long
as electric pump is within limit of Bing 54 (max 7Psi) ?
Again thanks a lot for kind patience to all Kolb friends
LageB
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