Flow control

I have found the mag 9.5 to be too much pump for my megaflow (which is rated at 600 gph), and will install a mag 7 when I get some time. I have found that the durso in the overflow starts to slurp if I have the pump running at full output, although others have not had the same experience. Currently, I throttle it down with a ball valve, which is fine. Valves downstream of the pump are ok, valves upstream cause trouble.

Short of installing a rheostat, I'm not sure how you would change the pump rpm. I don't know if it would be bad, but I don't know of anyone who does it.

Dave is correct in that valves downstream from the Mag are fine. The most elegant solution to controlling return flow that I've seen is a T immediately after the Mag output and a a GATE valve after the T.

The pump feels absolutely no back pressure as any head pressure caused as a result of a partially closed valve is diverted back into the sump. You can have to valve completely closed if you want to and the pump still would not feel a thing.

I metion the use of a GATE valve rather than a ball valve because GATEs are better for fine-tuning flow. You need at least 3-4 complete turns of a gate valve to get from wide open to fully closed whereas it's as little as 90 degrees with ball valves. Ball valves are superior for holding pressure (either ON or OFF). Unfortunately, PCV gate valves are big/bulky, more expensive and rather difficult to find on their own.

You'll notice that the higher end Beckett and needle wheel skimmers all use gate valves for "dialing in". I've got a ball valve between the Mag5 and the Remora skimmer in my tank. I couldn't find a 1/2" ID gate valve and one would probably be too intrusive on the inside of the tank anyway. It took forever for me to tweak the ball valve in order to get the skimmate that I wanted.

Crown Royal said:

I metion the use of a GATE valve rather than a ball valve because GATEs are better for fine-tuning flow. You need at least 3-4 complete turns of a gate valve to get from wide open to fully closed whereas it's as little as 90 degrees with ball valves. Ball valves are superior for holding pressure (either ON or OFF). Unfortunately, PCV gate valves are big/bulky, more expensive and rather difficult to find on their own.

You'll notice that the higher end Beckett and needle wheel skimmers all use gate valves for "dialing in". I've got a ball valve between the Mag5 and the Remora skimmer in my tank. I couldn't find a 1/2" ID gate valve and one would probably be too intrusive on the inside of the tank anyway. It took forever for me to tweak the ball valve in order to get the skimmate that I wanted.

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If you are looking for small gate valves, check www.usplastic.com. I got one for my Ca reactor there. I totally agree that gate valves give much better control, but the ones I have found also restrict the flow too much when fully open. I generally only use gate valves in situations where I need fine control and don't need to maintain high flow.

lbear said:

Thanks for your replay, Dave.
From the spec of Mag 7 and Mag 9.5, the flow rate is 420 gph and 750 gph each @ 5'. 5' is about the height of my tank and stand. 420 gph is probably not enough for reef tank but ok for FOWLR (72 gal).

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You'd probably want some powerheads in there too anyway, so that you don't have to rely on the sump return to create all your flow. With a couple of Maxijets, and the sump return, you could easily generate the "optimal" 10x turnover rate.

I wondering why there is no variable output pump available. Is there any way to DIY?

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The freshwater system I installed in our boat has a really neat variable speed demand pressure pump. Instead of a traditional installation, which has a "full-speed-only" pump and an accumulator tank (which stores some pressure to keep the pump from cycling too much during use), this pump senses the pressure in the line and adjusts its speed to pump only the necessary amount of water.

It would indeed be nice if a similar technology (but with a manual control instead of the pressure sensor) could be applied to a return pump, as it would make it a simple matter to optimize for the best flow / noise ratio.

However, I guess pump manufacturers figure that it's not worth their expense to incorporate such a feature, as it's pretty easy to add a tee and valve back to the sump to adjust flow. But it's something I'd be willing to pay a little extra for!

--Mike