Problem with DG

[DRGT]

I have a vacuum driven DG in my 57 Apache. I have vacuum pumps on each engine. Recently, my DG has been intermittment. My IA says he has never heard of an intermittment DG - they work or they don't. He said to double check to ensure it is uncaged. I did and it is. But on the last 4 (VFR) flights, it worked, it didn't, it worked, and then it didn't. I am hesitant to file IFR (actually delayed trips) until I am confident that it will work.

Anyone experienced this? Any clues to start trouble shooting?

[WLIU]

Hello,

I assume that you have a vacuum gauge and a valve to read the vacuum provided by each pump? So you must have good vacuum from both sides.

Next, when was the central filter last replaced? The DG gets stupid before the AH when the flow is restricted. And both instruments are actually driven by flow, the vacuum reading on the gauge only suggests that flow is present.

Could there be a hose that is coming loose under the panel? That might cause intermittent operation. But did the AH have problems at the same time?

Best of luck,

Wes
N78PS

[DRGT]

Thanks for the pointers. AH seems to be working fine. I have a selector switch that determines which engine/vacuum powers the DG & AH. TC is electric (thank God). It doesn't seem to matter which vacuum pump is selected.