Anyone running Mag-18 External? (Pic)

[Acroholic]

I have a Mag 18 that I am running to my Skimmer....
The intake fitting on the pump intake housing is 3/4".....
When I plumbed 3/4" fittings into pump and started running it, I found there is a slight cavitation noise coming from the pump intake housing.
I tore out all the 3/4" lines and fittings and replaced them all with 1" lines and fittings, since my bulkhead fitting is 1" anyway....
Now I am running 1" all the way to pump intake and it still makes exactly the same noise.....It's not loud by any means..but it is there and it concerns me...
Here is a pic of what I am talking about....Any Suggestions?

http://h1.ripway.com/lee646/MAG18.jpg

[Methamphetareef]

I ran a Mag 18 external for about a year. Same thing, not super loud, but you could definately hear it when it was running. Also I run my CA and ALK pretty high and this pump would freeze up every 2 months or so and require tear down and cleaning. I switched it out for a Poseidon P4 pump about 6 months ago. Dead silent and I haven't had to clean it yet.

[Acroholic]

Methamphetareef...:twitch: Funny Name..I guess your reef doesnt get much sleep.....J/K
Did you have 3/4" or 1" to your intake? Was it plumbed straight out of the sump or angled 90 out like mine?

[Acroholic]

Anybody else using a Mag 18 external?
BTW, anyone know what the GPH of the P4 is?

[sparks56]

most people dont recommend running mags external / i run the 18 in sump w/ no problems/ i think the t4 is 1250 gph

[Acroholic]

Why don't they recommend external use, it is dead quiet (except for the slight cavitation noise) and it runs cool, I just don't want any equipment in my water for the reason of heat transference.....

[sjm817]

The Mag will transfer a lot of heat to the water whether you use it internal or external. It is a water cooled pump.

[larryl]

I run Mags both submerged and external. It seems like with your plumbing changes you should have low enough restriction on the input to have gotten rid of any cavitation noise.

They also seem to run quieter if they are running against some level of back pressure. I'm using a Mag 12 for a return pump and found it was quieter if I throttled back on the output a bit (i.e. closed down the ball valve on the output a bit). It made things a fair amount quieter without reducing the flow by a huge amount.


Larry