CAT update.

The CAT uses a PPF (pleated paper filter), designed for use in fuel systems as its central pickup, compared to many other UAT products this filter is relatively large in relation to the container it is housed in. This is to make sure the surface area of the filter is as large as it can be which in turn removes the chances of cavitation which can occur when fuel restrictions are present.

The system when new is supplied dry, once fuel is added the filter takes on a characteristic where it freely allows fuel to pass through even during intermittent exposure to air (possibly during energetic flying and when the main tank is low). On the flip side if the fuel level in the CAT is allowed to drain down to below the PPF for extended periods, i.e. during transportation, travel or storage air will slowly bleed through the fuel soaked filter and into the PPF.

When the turbine next runs this air will at some point pass through to the turbine. The method as Oli states (in a new thread on this forum) is to run the turbine and purge the CAT whilst tapping it to dislodge any air that may be inside the filter.

The PPF is brilliant at stopping air passing through it during normal flying use but when air does bleed into it during situations mentioned above, its equally brilliant at keeping it inside!

As a rule of thumb once you fill your CAT leave the CAT fully fuelled at all times, it's how it was designed to be, any air which enters the CAT tank during filling with fuel can be removed by reversing your filling pump for a second or two when the system is full to suck out the air (make sure fill barb is uppermost).

Safe flying.

marcs