Return Pump Not Performing

[bluegoose972]

Guys,
Just jumping back into this hobby after five years off. Decided to build me a "craigslist" tank. Trying to find deals on everything off of craigslist and see how cheaply I can build this tank. Found an Oceanic tank (180 gal) with stand and sump (60 gal) for $500. Then I found what I believed to be a Mag 18 used pump. Cleaned it up and everything looks good. Plumbed it in to my two 3/4" returns with a T and turned it on. Good flow, but just not enough. There are two 1" dia returns and there isn't enough flow from the Mag 18 to overload even one of the 1" dia drains. Only pumping 6 ft of head and tried to keep the bends to a minimum, even using two 45 deg bends in lieu of a 90 deg elbow to smooth out the corners.

I pulled out the impeller and not seeing anything really wrong, like broken pieces...but have no idea how many hours the unit has been running. Could this be the reason for the limited flow? Any other ideas?

 

[gweston]

Mag's are pretty tough pumps, but could be the impeller is worn? I'd expect Mag may be able to help out.

I currently have a Mag 18 that feeds a 125 long, a 40 breeder, 20 high fuge all tied into 60 gals of sump. Same floor. Sump room is right behind the wall from the tank. I don't get anywhere near max flow capacity for the system I built (I need to upgrade the pump), but I am getting sufficient (not ideal) flow.

Mag I recall suggests that the return plumbing off the Mag18 actually be 1.5", not 1". Fine print I guess. But 1" shouldn't be a problem I'd think. In my system, the Mag18 goes right into a 1.5" run, where I branch off multiple 1" lines with ball valves. One to each display, as well as the fuge. The fuge has little flow, as intended. The 40B has flow, but could use a bit of supplementation. I directed most of the flow to the 125. I also have power-heads in there that I run during the day. They go off at night to keep the clowns from flying around while they sleep

Unsure what pump I'll end up upgrading to... eventually. Was eying one of the higher capacity Water Blasters (7k or 10k models) because their price point, flow rate, and energy usage seemed ok. External models are also viable, but they may need a higher budget.

 

[phk36]

pull apart the impeller it may have a cracked shaft . So pull the whole thing apart. The magnate my be out of round so you may need a new impeller it should be a circle not oval

 

[bluegoose972]

Opps...That may be my problem. The outflow on the Mag 18 is 3/4", so I used 3/4" PVC piping up to the "T" split for the 3/4" returns.

Was considering running 1" PVC pipe up to the "T" and then back to 3/4", but with the 3/4" inlet, I figured that was the controlling bottleneck.

Any comments about this?

Rick

 

[reefermad619]

The T is not a good idea. Your flow is hitting a brick wall then going left and right. Try using a "Y" instead. When I was T-ing off my return on a quiet one 4000, I lost about 200gph by using a T. If you want best flow, don't T off. Jut use one exit.

 

[sirreal63]

With the specs you have given, the mag18 is only putting out about 702 gph. If you upped the pipe to 1" it would be 896 gph and 1-1/4" pipe would be 1049 gph and 1-1/2" would be 1100 gph.

 

[bluegoose972]

I appreciate the feedback guys....Thanks. But I'm still a little confused. If the feed off of the pump is only 3/4" and can't be increased as it's part of the housing, won't that be the bottleneck of the return? Upsizing to 1" pipe should slow down the flow of the water, but the volume of water coming through the system will still be regulated by the pump outlet size....right?

Maybe I need to find a wall and bang my head for a few minutes!

 

[sirreal63]

It is a pump, it is pushing water, so the outlet size is not that critical. It leaves the pump under pressure. It is capable of pushing more water than gravity would flow through that 3/4" outlet, so the outlet isn't a restriction, but the size of the piping after the outlet can, and in the case of Mags, is a restriction. Some pumps handle head, or restriction better than others. A Mag is not a powerful pump, it relies on the outlet pipe to be a certain size to get the flow.