747-400 EICAS maintenance page - Aircon system
 

Anybody more technically minded than myself able to answer this question?!

On the EICAS maintenance page for the Air Con system, individual valve positions for the trim air valves are displayed. If a valve was locked mechanically into eg. 25% open position (as per certain MEL requirements) would this show up on the EICAS?

In other words, where does the EICAS valve position take its input from, electronic signal or physical (mechanical) position?

rgds
JD

I assume a rotary variable displacement transducer (RVDT) is used to send the valve position, will try and find more info.

Thank you SMOC... I am specifically interested in what should be displayed on EICAS in the event of a mechanically locked out valve. Rgds

I suspect the indication of the locked out "trim air valve" will be blank as the electrical connector is removed to manually position the valve.

Checked the MEL and as McBolt says:

We manually wind the valves for a certain chk we do and as soon as you disconnect the canon plug for these valves you loose your indication and it goes blank. If you lock a valve in a certain position for an MEL you have to disconnect the plug because you can not wind it with the plug on. With the plug on it will always run to the position that the pax temp master selector knob is set to in the cockpit, through the zone temp controller. The valves are under control of the zone temp controller it feeds the position signal from the valve back to the ztc then to eicas. Its not a rvdt it is a potentiometer. The MEL will tell you to wind the manual drive with an allen key so many turns. 30% open is 3/4 of a turn from the closed position. Hope this helps.