Tuesday, June 21, 2005

Quadruple Pump Failure

If you haven't read the posts before this post yet, skip this post and read down until you get to the post that ends by asking you what you think will happen if all four boost pumps fail. Unless you don't want to play the game.

Clearly something bad might be expected to happen if all four pumps in a system as complicated as that described below should fail n'est ce pas? You'd think. The thing is, if the #1 and #2 boost pumps fail in both tanks, leaving zero operating boost pumps, then four caution lights illuminate. No, the engine doesn't stop. The engine-driven boost pumps that deliver fuel to the fuel control unit and hence the engines at up to 850 psi is quite capable of lifting the fuel out of the tanks, through the fuel filters, through the fuel flow indicators, through the emergency shut off valves, to the engines.

You're not supposed to run it that way for long though. Without the low pressure boost pumps, the high pressure boost pumps will cavitate and wear excessively. Ten hours of operation with less than 5 psi pressure supply to the high pressure boost pumps, and they have to be overhauled. So the DC electric boost pumps boost fuel up to the engine driven pumps at about 22 psi, and then the engine driven fuel pumps pressurizes the fuel and shoves it into the engine.

1 comment:

Frank Ch. Eigler said...

Neato. I love hearing about clever design choices in complex airplanes. It's neat that it's not super different from my own little twin, with four fuel pumps that can partially back each other up.