Date: 08 Dec 96 04:12:31 From: "David G. Davidson" <firstname.lastname@example.org> Organization: http://rampages.onramp.net/~gerhard/tristar References: 1 2 3 Followups: 1
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Jean Ludovicy wrote: > I can't follow you John. > How does the packs, wich are responsible for an eventuel increase in > fuel consumption, know that there is an additional air leak at the > cargo door. > Do I miss something? I'm not familiar with the 747 but for discussion lets pretend that 747=757. The packs don't know that there is a leak, the pack valves are designed to provide a certain volume of air. On the B-757 each pack valve (acutally called a Flow Control and Shutoff Valve) is designed to provide 75 lbs/min of air to the pack (normal flow schedule). The pressurization system on the other hand can see that something is wrong if there is an excessive leak in the pressure vessel. If the outflow valve is fully closed and the cabin altitude is climbing, a low flow signal is triggered in the pressurization controller and the LOW FLOW fault light is illuminated. This may be an option on the 757 as our airplanes don't have the LOW FLOW light but our MD-80s do. In short, the packs can't compensate for a pressure leak, only the pressurization system can do that and only up to a point.