In general aviation light airplanes (C152,C172,PA28..) how does the engine driven vacuum pump work?How is it made? and if the filter of one of the gyro instrument is clogged would the vacuum indication still in the green arc? (The latest question bother me the most!)
It uses a system of vanes to draw air through the inlet port and expel it through the outlet port. The engine's lubricating system provides oil for lubrication as well as sealing the internals. The inlet is connected to the instrument and this provides the vacuum the instrument needs. To answer your last question, if the instruments are connected in series and then to the vacuum pump, and one of the instruments obstructs the air flow in the system, you may loose vacuum and instruments can become unreliable or stop working.