Boost pump -- in series or parallel to engine-driven pump?

[Kalibr]

On a conventional FI engine, are there any benefits to plumbing the boost pump in parallel to the engine driven pump? The way I see it, putting it in parallel, makes the system more complex because of additional tubing, connections, check valves, possibly additional firewall penetration. Can the engine driven pump fail in such a way as to cut off the fuel flow? If not, then I don't see a reason to consider plumbing the boost pump in parallel. What am I missing?

I've tried to research the issue and came back empty handed as far as airplanes are concerned. As far as fuel and other liquids outside of aviation are concerned, plumbing pumps in parallel is done to increase the flow rate, in series -- to increase head pressure. Neither is needed or desired in our application -- either the engine driven or the boost pump must provide sufficient pressure and flow in any case.

[Raymo]

The only benefit I see for parallel (have never seen one installed) would be if the mechanical pump diaphragm were leaking and dumping fuel out the drain, resulting in a higher fuel flow than you would see with the flow transducer further upstream.

This configuration would require a check valve to keep fuel from flowing back through the mechanical pump, as well.

[David-aviator]

Originally Posted by Kalibr

On a conventional FI engine, are there any benefits to plumbing the boost pump in parallel to the engine driven pump? The way I see it, putting it in parallel, makes the system more complex because of additional tubing, connections, check valves, possibly additional firewall penetration. Can the engine driven pump fail in such a way as to cut off the fuel flow? If not, then I don't see a reason to consider plumbing the boost pump in parallel. What am I missing?

I've tried to research the issue and came back empty handed as far as airplanes are concerned. As far as fuel and other liquids outside of aviation are concerned, plumbing pumps in parallel is done to increase the flow rate, in series -- to increase head pressure. Neither is needed or desired in our application -- either the engine driven or the boost pump must provide sufficient pressure and flow in any case.

Could be it is as it is because it is best way to go, established many years ago.

[Toobuilder]

I think you are overlooking the subtle detail that the boost pump is not operating 99% of the time. It's there to move fuel only when the engine driven pump can't. They are not intended to provide a compound benefit by working together.

[Kalibr]

Thank you! It's always been clear to me that the boost pump is there to take over the duties of the engine driven pump in case it fails. I've heard someone suggesting that it would be a good idea to plumb it in parallel. So, I was wondering what benefits might there be to that.
Off to wondering about something else now