Supreme Mag pumps by Danner Mfg are a popular choice for reef keepers. Here's the flow chart that was obtained from MarineDepot.com's site. It recently moved and after a lot of searching, it was simply easier to take a screen shot and place it here. Marine Depot sells every model made: MarineDepot.com - Danner Pumps
Servicing Supreme Mag Drive (Pumps):
When you install a Mag drive on your system, such as a return pump or a closed loop, that isn't the end of it. The pump needs to be cleaned and inspected to keep it running at peak performance. Ideally, it should be connected to your plumbing in a way where it can be easily removed. One nice option is the use of a "union," which is two threaded parts held together with a threaded collar. By twisting the collar counter-clockwise, the pump can be disconnected from the plumbing and is ready to clean.
One major complaint about the Mag drives is that the cover plate can be cracked. Hopefully these suggestions will help avoid that situation. Put your pump on a solid surface, such as a countertop. Carefully unscrew the screws holding the molded plastic cover plate in place. Set these aside where none can be lost (or fall down a drain!). Lift off the cover, trying not to pry it away at an angle. Work it off gently, pulling upward. Next, remove the impeller, which is the magnetic-driven propeller.
Using a bottle brush or even a tooth brush, clean the pump's surfaces and the impeller cavity. Brush off the o-ring as well. Using a smaller bottle brush, clean the output pipe to rid it of slime and debris. Clean the inner area of the cover plate, including the intake hole. Clean the impeller with a sponge or toothbrush, and inspect it for damage. If it is damaged, it should be replaced. Put the impeller back into place, and align the cover plate into position and press down firmly.
Now here's a trick to avoid stripping the screw holes or cracking the cover plate: Insert one screw into a hole, and using your screwdriver press down (moderate pressure) and twist the screwdriver in reverse, as if unscrewing the screw. As the screw turns, you will feel a small drop of the screw at one specific spot. This is when the threads of the screw have lined up with the threads in the plastic frame. At that point, tighten down the screw firmly, but not excessively. At the opposite corner, install the next screw, again using the reverse-twist method until the screw drops into place and tighten. Continue replacing screws on opposing sides, until all have been screwed in. By following these steps, excessive torque won't be placed on the plastic cover plate, and the screw holes won't be stripped.
Reinstall your pump by tightening the union, plug it in, and enjoy trouble-free flow.
If you ever have problems with your Mag drive, the company warranties it for three years from the date of purchase. You can find their contact information here. One pump failed within a few months, and they sent me a replacement. I shipped them the broken one in the same box with a pre-printed label they included. Good customer service.