>However, unless the fuel pump is downstream of the OV relay, it won't
pump for too long, subjected to full unregulated output from a failed
regulator! This is one misfeature of OV protection as might be wired
for the 914, compared to the 912 with a mech fuel pump. If there's no
OV relay, the battery and other items on the bus will clamp voltage to a
temporarily safe (average) voltage level, won't pop the pump CB, and
allow more than enough time for one to take corrective action before
harm is done to the battery. Provided one has clear panel warning of
the OV condition.<
The reason for an electrical pump to be connected to the regulator output is
not for regulator failure but to cater for a major failure in the rest of
the system. With the main fuse blown the regulator will cope quite
adequately with just the load of the pump. In the case of a regulator
failing to high voltage the other pump, isolated from the effects of the
regulator by the OV unit, will be working just fine from battery power.
If the load is too great for the pump connected to the regulator it will pop
its c/b or blow its fuse. No big deal as the other pump is providing fuel
pressure.
This way we are catering for most significant single failures. If you want
to cope with double failures I doubt whether you would be flying in a single
engined aircraft anyway.
Is there any form of corrective action that needs doing manually? What
action are you going to take if you have an OV condition? I would suggest
you would isolate the regulator from the rest of the system. Why not have
the OV unit do this for you?
I don't claim to be an expert in this area but I would want to be very sure
of my knowledge before ignoring the advice of Bob Nuckolls.
Nigel Charles
|