For those of you who have read about yet another vacuum pump failure on N415WM, I want to provide some details of what has happened. First, the latest vacuum pump failure is my SIXTH! in less than 400 hours. The last pump lasted but only 30.5 hours.
This failure, like the others, ended in a sheared shaft on the vacuum pump. The temp on the vacuum pump (thanks to some telatemp strips from Bill Marvel) topped 230 and was less than 390. The telatemp strip for the temps between 230 and 390 was not available when the fifth vacuum pump was installed. According to Airborne the round sticker on the side of the pump is also an Airborne telatemp type sticker that turns brown when it gets over heated. Initial sense is that heat may NOT be an issue.
Over the past five vacuum pump failures various things have been identified and tried. Each time the thought was that “this” was the problem. Whatever it took to get the problem solved was undertaken, done, and supported by Cirrus. The last time, Airborne had our maintenance shop (Del Monte Aviation - MRY) take vacuum readings at various points in the vacuum system. The readings, which were incidently taken with a brand new, freshly calibrated vacuum gauge sent to our maintenance shop from Airborne, were sent to Airborne. Airborne, based on those readings said the problem definitely was a leak in one of the two instruments (AH or DG, or AI and HI, if you prefer). Cirrus didn’t fool around and sent two new instruments as replacements. Cirrus also wanted to swap out the fifth vacuum pump at the end of 25 hours to inspect the pump prior to failure. A communication problem prevented that from happening. Despite the definitive answer from Airborne and the warm feeling all concerned had in finally having “solved the problem” the sixth pump failed!
In the past, the entire vacuum system has been replaced, which included both the instruments that the vacuum system drives! It included new vacuum hoses, ‘T’ valve for the backup vacuum system, new filters, etc. It seems everything has been tested, checked, and/or replaced except the engine drive shaft for the vacuum pump.
It was suggested by several that engine harmonics could set up a vibration that could cause the pump to fail. This time Cirrus has directed that a new DG (the replacement had a heading bug problem unrelated to the vacuum issue) and vacuum pump be installed. Prior to installation the engine drive shaft for the vacuum pump was double checked, an Airborne tech rep, who happens to be in CA on “tour”, will likely stop by to look over Del Monte’s shoulder, and after double checking the vacuum pressure settings the plane will be flown over to TOP GUN in Stockton for engine/prop dynamic balancing.
FLASH: Just got word as I was writing this that TCM apparently now believes that either the starter assembly on the back of the engine that also contains the drive shaft for the Vacuum Pump may have some abnormal axial movement Â… to me that means it wobbles. The wobbling likely caused the vacuum pump nylon shaft to overheat and then shear. At the moment I have emailed Cirrus about seeking a replacement starter assembly. The only other thing that was mentioned by TCM was that starter assembly drive shaft “bottoms out” in the vacuum pump, which can also cause premature failure. The cure for the latter is to “shim” the vacuum pump farther from the engine Â… i.e., more gasket material I suppose. Ironically, this is what the Del Monte maintenance shop had said from nearly the beginning that it was likely the starter assembly. I suspect the ideal of replacing it was held to the end due the time and expense of the part as well as the installation.
According to information I am getting from Cirrus, I have the only plane that has had multiple vacuum failures. Anybody else?
Maybe the problems with the vacuum pumps pushed Cirrus to embrace the “all electric” SR22!? In any event, the SR22 will not have vacuum problems .