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I recently wondered if my Duke's valve was working correctly.  I found the outflow dirty (from construction debris), and sent both components for service; they cleaned it, upgraded it, and fixed some things ($660).  Still, it didn't seem to be very responsive with the panel control changes.  The cabin would pressurize to 3 psi quickly, and then I see this increase to 5 psi with altitude and remain fairly stable.  Rate changes on the controller had no real effect.

So I disconnnected the harness to the Duke's valve and went flying...the cabin behaved the same.  That's right, completely disconnected, the cabin pressurized inn the same manner.

The harness has wiring labels that are easily confused, so I wondered if this was the case.

I went through all the connections on both components and confirmed every pin is correct except the uncertainty of Pin 4 on the outflow valve...this is the ground switch that closes the 12V circuit to power the valve.  This is, on the ground, checking continuity, an open wire...not connected to ground.  I can not tell if it closes with airspeed and gear up.  Without power, the Duke's valve is not participating at all in cabin pressurization.

Recall the actual valve is to open when gear goes down or airspeed gets low (to avoid cabin retaining pressure on the ground).  But if Pin 4 removes GROUND as the action, then apparently the solenoid drive outflow valve is fairly closed already, and does not actively open (N.O.) in the absence of power.

For the valve to come alive, it needs the 12V circuit to close (pin 4 to ground) to activate the device.  I must assume this is not happening, since all other connections are confirmed.

Again, all wiring, power, dump switch, connections with controller...all are correct.  But apparently, there is a persistent problem with Pin 4 giving ground to the outflow valve, since the valve seems to be completely uninterested in manipulating cabin pressure.

I plan to fly with the outflow valve disconnected again, and place a circuit test on Pin 4 opposite 12V to see if I can get confirmation that the circuit closes with airspeed & gear up.

Any other ideas how to diagnose the problem?  Can you help with a specific set of checks to determine if the valve (behind me) is working?

I want to avoid on the ground gear swing while a friend blows into the pitot tube...what a scene that would be.

Jeff Liegner

The "Dump Switch" is a simple throw switch on the panel, closing ground for the valve.

The "Vacuum Switch" is the key circuit.  12V on Pin 3, and Pin 4 is the questionable ground connect that is currently open.

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