The PS-525 tester has separate, independent pumps for vacuum and pressure. Each are activated with their own switch as the operator deems necessary. Furthermore, the pressure sensor on the Airspeed side is independent of the vacuum system, as it is not a differential pressure sensor. For airspeed measurements, which are based on differential pressure, the airspeed microcontroller obtains an electronic reading of the pressure in the vacuum side, and subtracts it mathematically from the pressure side to obtain the differential value.
The PS-525 incorporates reservoirs (holding tanks) for both the vacuum and pressure systems. The pressure and vacuum levels within these tanks are reflected in the pressure and vacuum gauges on the front panel. These gauges enable the operator to monitor the pressure and vacuum, and then activate the pump switch for the system on an as-needed basis. This eliminates the need to keep the pumps turned on at all times, and extends the pump life and battery charge. The gauges also enable the operator to see if the pressure or vacuum levels are dropping quickly, in the case of a leak in the aircraft system, and respond accordingly.
A diagram of the internal plumbing system of the PS-525 is as follows: