Ralf asked:
I
am wondering if I should move my pump and the pressure switch for the door seal
in the door (Lancair IV-P). What would be
the best way to get the electric power in the door – should I run a cable
from the door to the fuselage or should I go with this switch that makes
contact when the door closes. I would need 4 wires (2 for the pump and 2 for
the switch).
My door seal pump is mounted on the door, and I recommend this method
for several reasons. Lancair now sells a small, high quality (and priced
accordingly) pressure pump that fits much better than the old-style pump.
Consider investing in the new pump if you use this.
Mount the manual seal control valve in the door as well, and use
an SUV sliding door-type pair of contact buttons to transfer power/ground to
the door. I actually used three-button units on my IV-P so I could also operate
a “DOOR UNLOCKED” warning light via a third lead that is closed to the
common ground when either door latch is open. Whether you use the warning light
circuit or not, install a fuse or CB in a lead from your primary/main power
buss and then directly to one contact button. Run this lead through your door
seal pressure switch and then to the pump. Run a ground to the other button and
then from the button to the pump.
Theory of operation: When the door is open, no power can be
applied to the pump in the door (contacts open). Any time the door is closed
AND the power buss is hot, the pump can be energized. If the door seal control
valve (toggle switch) is in the off/vent position, the pump stops as soon as it
builds pressure in the short piece of line between the pump and the control
valve (assuming you have correctly installed the pressure switch between the
pump outlet and the seal control valve). When the door seal pressure switch is
on, air is diverted into the door seal until the set pressure is reached, and
then the pump turns off. My system works well and provides a “built in”
test of the pump/circuit each time I close the door, as the pump runs for a
couple of seconds (unless it’s been closed too recently for the pressure
to leak down). Not necessary, but installing a one-way check valve
between the pump outlet and the pressure switch allows the pump to “unload”
between periodic starts to maintain seal pressure—if you have any leakage
in the system.
Hope this helps.
BOB