Don,

 

Let's think about that.  What could have caused the pressure switch contacts to fuse in the closed position?  Was it an incredible surge from a power inrush to the intermittent relay coil, bouncing switch contacts affected by a surge from the collapsing coil at its release or what?  Of course, contact resistance from carbon build-up can eventually result in enough arcing to possibly fuse the contacts.  I'm sure a diode on the relay coil would ameliorate everything but dirty contact arcing. 

 

My experience with a test pump motor was that it would not run when power is applied to both sides of the pump. 

 

I cannot understand how the gear switch in the down position can shunt power over to the up relay even if the up pressure switch contacts are fused - I can see how the pump would run continuously if the gear up switch was selected and the fused pressure switch would not shut the relay off when the pressure target was reached - that is the pump would continue to run and the pressure would be limited to that set in the pump up pressure relief valve.

 

Scott Krueger

 

Similar incident, landing gear comes up as I am landing!!! Found the high
pressure switch fused closed! Added diodes to protest the pressure switches
and ignition. Earlier, the same thing happened to the ig relay, fused
closed!!


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