View Full Version : External mag 18 rather loud... Possibly not air tight?

09/30/2007, 10:55 AM
Its not the hum that loud... it kinda sounds like there is something in the impeller casing, maybe air? I was thinking that maybe it wasnt't air tight. I was thinking of adding another rubber ring to the impeller casing. i dont think they are that air tight because if you don't tighten them enough they leak. Also i may need to clean this. Does anyone have any ideas what is going on?

Also, when i turn the outgoing ball valve to about half open, the sound goes away... but i want to run the pump at full speed w/o the sound.

09/30/2007, 11:42 AM
It could be cavitating. What size plumbing are you using on the return? Rule of thumb is to double the output size. I think the Mag 18 has a 1" output so you should use 2" plumbing.

09/30/2007, 12:49 PM
Sounds like it is starving on the suction side. Intake piping should always be oversized, as short as possible, very few if any fittings or restrictions and have as much water as possible over the pump for positive suction head.
How is it plumbed?

09/30/2007, 01:05 PM
Hmm.. well the mag 18 has 3/4" fittings, and i have 3/4" piping :( I will take a pic here in a little bit... but it has a setup like this... http://www.melevsreef.com/closedloop.html (without the wave maker thing.)

If it is being starved... do i need to only change the intake or the out piping too? the out piping is a single 3/4" tube that has a T split into 2 outflows.

09/30/2007, 01:11 PM
The intake should be 1.5" and the outlet should be 1".

Up and over the back suctions like that are really hard on a pump as it greatly reduces the flow to the pump due to the fittings and restrictions. It needs to be at least 1.5" even if you had the tank drilled and were feeding the pump directly.

09/30/2007, 01:19 PM
what would you suggest i do then? the return was a pain to put together but the intake was easy... would i be able to get away with putting an up and over intake with 1.5" and keeping the return alone?

09/30/2007, 01:22 PM
Probably. It wont be the best thing for flow but it will get rid of the cavitation noise. AZDesertRat is right on.

09/30/2007, 01:29 PM
You have way too much pump for what you are trying to do. A Mag 18 is rated at 1800 GPH, thats 30 gallons per minute. To put that in perspective your average garden hose if 5/8" or 3/4" and flows about 13 GPM at 50 psi of pressure. You are trying to shove double that volume through a single 3/4" pipe with hopefully little or no pressure exerted. You will be lucky to get 300 or 400 GPH out of it at best and thats a big waste of energy and will create lots of unneeded heat. If you are set on Mag pumps look at a 7 or 9.5 for 3/4" to 1" piping. I am not a fan of Mags since they are energy hogs, inefficient, noisy and run hot. OceanRunner of Eheim are both much better choices. I run a OceanRunner 3500 through a drilled closed loop using 1" pipe in and 1" reduced to 3/4" at each of 2 LocLine outlets. It used to go through a SQWD which cut the production by at least 1/3 so I changed to an Ocean Motions Squirt 2 way and it does not slow the flow at all.

09/30/2007, 01:38 PM
Well I'm kinda set on using the mag 18 since i already own it... the one think i don't understand is why it has a 3/4" fitting if it needs 1.5" piping. So I will probably set up a 1.5" inlet.

What if i make the return pump start at 1.5" and then get a T split into the 2 3/4" returns, that way there is still a larger area of out let (i know 2 3/3 diamters dont have the same area as 1 1.5" pipe area)

09/30/2007, 01:45 PM
That would really help but you still have way over double the pump for the plumbing. Heat and power consumption will be issues.

09/30/2007, 01:58 PM
I may sell it to my mom as a pond pump and get some circulation powerheads or something... im sick of hassling with things