While flying VFR in seriously clear conditions last week I experienced an abrupt vacuum pump failure (Rapco dry pump). The flight was purely visual, I was not using the DG to navigate nor was I using the AI. Just noticed the low vacuum light in my scan, and then saw that the vacuum gauge was out of the green.
I had read that vac pump failures were often not noticed at first as it took time for the gyros to spin down. I can verify that this is correct. It was probably 5 minutes before the DG became sluggish, and shortly thereafter the AI slowly started indicating a slow descending left turn. I can see how this could occur so slowly as to not be noticed if you were in the soup!
Thanks to the generosity of a VAF member, I have a replacement pump installed and everything is working again.
I just had to take the old pump apart to see what went wrong with it. I was expecting to see broken vanes (pump has about 700 hours on it) but they looked to be in good shape and not excessively worn. What had failed was the coupling (plastic / nylon)--just sheared in two parts.
Is this a normal failure mode? My filter was replaced last condition inspection and the gyros are relatively new so I don't think the load on the pump was excessive.
This is really an intellectual exercise as much as anything. I am taking the plane (RV-6, 2001) down this winter for upgrade to glass panel upgrade and the vacuum pump will go at that time.
I had read that vac pump failures were often not noticed at first as it took time for the gyros to spin down. I can verify that this is correct. It was probably 5 minutes before the DG became sluggish, and shortly thereafter the AI slowly started indicating a slow descending left turn. I can see how this could occur so slowly as to not be noticed if you were in the soup!
Thanks to the generosity of a VAF member, I have a replacement pump installed and everything is working again.
I just had to take the old pump apart to see what went wrong with it. I was expecting to see broken vanes (pump has about 700 hours on it) but they looked to be in good shape and not excessively worn. What had failed was the coupling (plastic / nylon)--just sheared in two parts.
Is this a normal failure mode? My filter was replaced last condition inspection and the gyros are relatively new so I don't think the load on the pump was excessive.
This is really an intellectual exercise as much as anything. I am taking the plane (RV-6, 2001) down this winter for upgrade to glass panel upgrade and the vacuum pump will go at that time.