I agree with "Koi Aquaponics" statement. On other pond filter systems I have designed, I came up with a "Power Outage" scenario where I store compressed air utilized within a simple pneumatic switch which during a power outage, the "Naturally On" electric pneumatic switch shuts off. This in turn sends pressure to a 4" PVC pneumatic valve which shuts off (or on) several valves to re-channel water accordingly. Question for FREEDERUMFILTER... Instead of plugging the recirculating pump(s) into your Control box (which shuts off if there is a problem), plug in the electrical side of the pneumatic valve into this socket, and use it to re-channel the water flow to bypass the drum filter and keeping the pumps running.
You need to design a bypass channel for water to continue to flow through in case the screen or motor is problematic. That way the outlet pumps can still circulate water when the RDF is off. I have not seen anyone managed this but I see it being a necessity. Perhaps make some water tight covers on the round end of the drum be removable with thumb screws. All you need is about 3x4" panels to allow water flow through. You're using stainless steel so rigidity should not be a problem.
