Brian
On page 14 of that report there is a diagram showing a typical suction system. The arrows indicate flow and it looks like the filter, if it were to become blocked or partially blocked, would cause a suction pressure indication as high as the relief valve would allow and the reduced flow of air across the gyro rotors would cause the gyros to spin slower.
Is that the case? And would a leak on the suction side of the gyros also cause slow speeds but a lower pressure indication?