Yep, I can attest that Old Faithful was exactly what happened on my recent post maintenance test flight as soon as the header tank was pumped full. The gas shot straight out of the fuelcap vent and back onto my windshield with a vengence.
That pump can move some fuel! Dave Winters This document is for viewing and use only by the intended recipient. If this document is received in error, please notify the sender and destroy it promptly. Winters Patent Law Offices, 2277-C Suite 237 Wilma Rudolph Boulevard, Clarksville, Tennessee 37040-5898, United States of America, Telephone: 931-906-4445, Facsimile: 931-906-0131, <http://winterspatentlaw.com/> http://WintersPatentLaw.com From: [email protected] [mailto:[email protected]] On Behalf Of William R. Bayne Sent: Wednesday, April 29, 2009 8:10 PM To: ety Tech Subject: Re: [ercoupe-tech] Fuel Pump Restrictor Hi Chris, A fuel pump and a TRANSFER pump are functionally quite different even though the hardware and terminology are identical. The Ercoupe "fuel pump" is merely a transfer pump and is not critical to flight. 1. Way more fuel than the engine can burn is sucked out of the balance line between the two wing tanks and pushed under pressure through the restrictor. 2. The restrictor reduces the huge excess of fuel transferred at full pump pressure to a lesser excess which is forced under relatively low pressure into the fuselage, or header tank. The flow restriction causes the pump to cavitate; thus reducing the "load" of a pump operating at full capacity to that of the required capacity. A tip of the hat to Fred Weick for that bit of "magic on the cheap". 3. The lesser excess still causes the fuel level in the header tank to rise until it reaches the tank's overflow intake, which it enters and flows by gravity back to one or more wing tank(s). 4. The header tank cap is vented to atmosphere in every ATC 718 and 787 airframe to assure that fuel in the header tank can flow freely by gravity to the gascolator, carburetor and engine. The header tank cannot be pressurized in normal operation and still function as intended. Without the restrictor the pump would transfer fuel at a rate in excess of the header overflow system to return and as the fuel level rose to the level of the fuel cap fuel would be ejected (visualize Old Faithful geyser) and distributed across the windscreen and likely further. This happens more than it should when the restrictor is removed or omitted by a mechanic unfamiliar with the Ercoupe (et al) design. It is true that once all fuel in the wing tanks the engine could not burn has been thus ejected, the pump has no measurable load whatsoever ;<) Regards, William R. Bayne .____|-(o)-|____. (Copyright 2009) -- On Apr 29, 2009, at 13:47, Chris wrote: On the restriction of the fuel pump outlet. It seems to me that it would be more efficient to let the fuel pump free run without the restrictor and let part of the pressure bypass back to the inlet. Wouldn't that take some of the load off the pump? Am I missing something here? Chris 99674 in restoration '--o-O-o--'
