It's not always recommended to mount upside-down. E.g. Laing DDC manual states it must not be mounted with the motor pointing up.
Primary reason for mounting the pump lower than the res is to keep the pump inlet flooded during the filling process. Well with most pumps it doesn't matter; the DDC must be one of the few exceptions.
If you mount a DDC upside down gravity will be pulling the little impeller away from it's housing.. not good!
Yeah, best bet would be to email the appropriate manufacturer and ask them, based on the pump you're thinking about. RwD
Some pumps do not mind in what position you mount them, as long as it is below the reservoir (waterline) and so that no air can get trapped in the impeller chamber (the pump outlet generally needs to be higher than the chamber itself). The Eheim's and older Swiftech MPC 600's are such pumps. In some pumps however, the impeller is balanced on a bearing in the magnetic field of the drive coil and on a lubricating cushion of the liquid that is being pumped, which minimises any friction and wear and thus ensures long life, but relies on the pump being mounted the right side up. The Laing DCC is one of those.
