What does this switch do?

[jackn]

It's located on the back of my ki-256 ai. Looks like a vacuum switch. Does it shut off The a/p if vacuum is lost?

[kortopates]

That should be for your Low/High vacuum annunciator.


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[Schinderhannes]

On a different note the use of teflon tape for sealing vacuum system fitting is not recommended.   

[Guest Mike261]

1 hour ago, N9495V said:

On a different note the use of teflon tape for sealing vacuum system fitting is not recommended.   

i think it may be prohibited.

[jackn]

Thanks Paul, makes sense. Ki-256 use teflon tape normally for the installation. Don't use for fuel system. Anyway, came from the factory in 1987 that way. 

[glenn reynolds]

The issue with the teflon pipe tape is not the teflon but the individual applying said tape.  It MUST be wrapped so that the first full thread (most people use two to be safe) Thread grooves have NO tape so there is zero chance of getting teflon "bits" or "strings" into the vacuum system as this contamination will cause failure of equipment.  As too many folks don't get this right, it is a common practice to tell folks not to use it at all.  The damage isn't just from excessive initial application, but on the removal of "tefloned" fittings it is normal to leave behind in the female fitting strings of teflon which must be removed 100% or same issue.  My point is that if there are ALREADY teflon tape fittings on the vacuum system it would be a really bad idea to take it apart just to remove the teflon.  there are paste pipe thread sealants which can be used, however the same exact rules apply, the paste sealant must not be allowed into the system, thus be very careful to only apply it behind the first male thread groove (and never the female fitting).

[Jerry 5TJ]

On 11/30/2016 at 6:24 PM, jackn said:

It's located on the back of my ki-256 ai. Looks like a vacuum switch. Does it shut off The a/p if vacuum is lost?

 

No.  With most King AP systems if vacuum is lost the autopilot follows the gyro until it reaches trim limits. 

[jlunseth]

41 minutes ago, Jerry 5TJ said:

No.  With most King AP systems if vacuum is lost the autopilot follows the gyro until it reaches trim limits. 

I had my vacuum go out in flight, fortunately VMC, and that is exactly what it did.  It takes the gyro awhile to slow down and tumble, so I stupidly left the AP in charge for awhile, while I told ATC.  The gyro started to tumble and the plane started to gain altitude because the falling AI was saying it was in a pitch down attitude.  Caught and corrected quickly and no issues, but the moral of the story is if the vacuum fails and the annunciator light comes on, disconnect the AP asap and don't trust the AI at all.