| vacuum assist - again [message #75652] |
Thu, 04 March 2010 13:26  |
jayrabe
Messages: 509
Registered: June 2009
Location: Portland, OR
Karma:
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Senior Member |
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The flow of information and opinion is just a bit overwhelming at times to this relative newbie with only marginal auto mechanical experience. Thanks in advance to all for your patience.
I'd earlier been persuaded by the horror stories that I wanted to add an aux vacuum pump as a backup in case engine dies. So I'm sitting here waiting for time and budget to allow the mod, and along comes highly respected Jim Bounds saying it's a bad idea. Near as I understand, Jim is basically saying that the system is good enough as it is, and adding any new components/wiring/plumbing adds additional failure points, and THAT is a problem, since a failure to any point of this critical safety system can be disastrous, and more failure points means higher risk/possibility of failure. Jim please correct me if I'm misstating your position.
OK so far?
So now to the reservoir. I'm persuaded by GeneF that the reservoir by itself does not give you enough reserve in case of engine quitting, but Rob's recent post about adding a reservoir AND an aux vacuum pump seems pretty robust. Is this overkill?
Anyway, I'm trying to understand how all this works. I've redrawn Robs schematic,
http://www.gmcmhphotos.com/photos/showphoto.php?photo=32555&title=p3010029b&cat=5408
So first off, in normal operation, the engine manifold draws what? 15-20"? And with the check valve between the reservoir and the manifold, the reservoir will basically always be at that highest vacuum level, other than being drawn down by using the brakes. So then the aux vacuum pump only comes on when it's internal pressure switch reads below what? 5"? 10"?
OK, but what's the advantage/disadvantage of plumbing it this way rather than having the aux pump sucking down the reservoir basically in parallel with the engine manifold (still isolated with check valves, of course)? This is apparently the way GeneD has done it (though I agree with other posters that it seems a bad idea to have the pump require a switch rather than coming on automatically when low vacuum is sensed.)
http://www.gmcmhphotos.com/photos/showphoto.php?photo=32556&title=p3010030a&cat=5408
And the option LarC described, with the aux pump in between (in series) with engine manifold and booster, seems like a bad way to go IMO...
Anyway, just trying to get a better understanding of these things. Thanks for all the input.
J Rabe
76 Palm Beach
Portland, OR
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