The reason why the mechanical pump is the backup and not the other way round
is easy to explain:
The mechanical pump do not deliver as much pressure as the electrical one.
On the 914 you will need an fuel pressure of
Airboxpressure + 0,25 bar , 3,63
Airboxpressure + 0,15 bar , 2,18
Airboxpressure + 0,35 bar , 5,08
At Take Off the engine produce an manifold pressure of 1350 hPa = 39,9 in.Hg
= 19,6 psi
That means, you need a max. Fuel pressure at the carburetor of 24,7
The mechanical pump delivers 0,15 bar up to 0,4 bar(5,8 psi). Do you see
That's the reason why the mechanical pump can feed the engine only up to
~2000m with ~55% power and can works in this situation only as an EMERGENCY
equipment to bring you with reduced power to an airfield. . (Better than
You have a fine explanation of the Fuel pressure system in the Maintenance
Manual on pages 34&35
I hope this helps and bring a little light in the complicated 914 fuel
system. This is one of the reason, why the 914 is
so much expansive vs.the 912S
Why should the mechanical pump ( if you can fit one) be the 'back up pump?
It would seem sensible to adopt general G.A., practise and have a
permanently running mechanical pump and electrical back ups which are used
only for take off and when below 3000ft on the approach.?????
_-= - The Europa-List Email Forum -
_-= Use the Matronics List Features Navigator to browse
_-= the many List utilities such as the Subscriptions page,
_-= Archive Search & Download, 7-Day Browse, Chat, FAQ,
_-= Photoshare, and much much more:
_-= --> http://www.matronics.com/Navigator?Europa-List _-============================================================
_-= - List Contribution Web Site -
_-= Thank you for your generous support!
_-= -Matt Dralle, List Admin.
_-= --> http://www.matronics.com/contribution _-============================================================