Maytronics Dolphin M400 / M500 impeller cover assembly - 9991045-ASSY

Maytronics Dolphin M400 / M500 impeller cover assembly

This is the genuine OEM impeller cover assembly (part 9991045-ASSY) for the Dolphin Supreme M4 and M5 platform, sold under the M400 and M500 model designations. It sits over the impeller housing on the top deck of the robot, sealing and protecting the pump cavity during every cleaning cycle.

What this impeller cover does in the Dolphin

The impeller cover closes off the impeller housing, maintaining the hydraulic seal that allows the pump to generate suction. Without a correctly seated cover, water bypasses the impeller chamber, suction pressure drops, and debris pick-up fails. The cover is also the access point specified in the official M400/M500 user instructions for routine impeller cleaning — you remove it, clear any debris around the impeller housing, then refit it.

Which Dolphin models it fits

This assembly is confirmed for the Dolphin Supreme M4, Dolphin Supreme M5, Dolphin M400, and Dolphin M500. All four share the same chassis and impeller housing geometry. Do not fit it to other Supreme or Dynamic variants without verifying the housing dimensions match.

Signs it needs replacing

Inspect the cover if you notice a visible crack or chip in the housing, if the cover no longer sits flush after routine cleaning, or if suction has dropped despite a clear impeller and clean filters. A cover that no longer seals correctly allows air ingress into the pump circuit, which degrades flow rate immediately. Discolouration or warping from chemical exposure is a reliable indicator that the plastic has fatigued and the cover should be swapped out proactively.

How to install it

Unplug the power supply before starting. The cover is secured with two Phillips-head screws into the top of the cover assembly — remove them, lift the old cover clear (a flat-head screwdriver used gently as a lever helps if it is seated tightly), then position the new cover flush with the surrounding assembly and refit both screws by hand before final tightening. The official manual explicitly warns against using a power drill, which risks stripping the threads. Total job time is under five minutes.