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LC20 Hydraulic Pump Wiring Considerations:

1.  Lancair wiring provides for two circuit breakers, 50 amp for the pump and
5 amp (or smaller) for the relays.  They also state that during any testing,
to pull both breakers.  Disengaging both is not always done -- "I forgot",
they are not co-located, one is a breaker and the other is a fuse or whatever.
If the main power bus is activated and only the pump breaker is opened, then
the up or down relay will be activated (depending on the position of the gear
switch) if the corresponding pressure switch is not sensing enough pressure
because the pressure has leaked down or the gear extension valve is open.  The
"gear transit" light will not be on because the power for it comes from power
being sent thru the relay contacts to the pump and that circuit was de-
activated by pulling the pump breaker.  This means the "intermittent use"
relay could be engaged for the length of time of the testing (in my case, 4
hours).  The  heat build-up in the relay can result in melting internal
coatings and causing the "selenoid" plunger to become stuck in the "picked"
position.  Removing power from this relay will not open the contacts and the
real excitement begins when the pump breaker is reset.  Of course, moving the
gear switch to the other position is only an attempt to run the motor in both
directions at once.  Yikes!

The solution (after replacing the screwed up relay) to prevent this is to
cascade the 5 amp relay power breaker (or fuse) off of the 50 amp pump breaker
so that when you pull the pump breaker, no power is available for the relays
either.

2. Locate the 50 amp pump breaker where it is easy to get at -- not on the
baggage bulkhead.  It may be desireable to stop the pump quickly whilst flying
solo and reaching behind is not safe (remember John Denver).  Since my battery
is behind the co-pilot seat, it was not much more wire length to put the pump
breaker just forward of the glove box cover, on the top of the between seat
console.  Because I have second-generation pressure switches, sometimes the
pump will run too long on a gear-up request and pulling the breaker for a few
seconds helps the pressure switch settle down.

3.  If the wire to the "gear transit" light were shorted, it would surely burn
before the 50 amp breaker popped.  One should, for safety's sake, put
isolation diodes at the indicate (I) position of the pump relays and an in-
line fuse on that wire.

Scott Krueger
N92EX