What size return pump

[FishieNut]

I have a 1.5" drain from my tank to my sump -- I acutally have two 1.5" drains from the tank to the sump, but one I'm going to use for a closed loop with an Super Squirt system from Oceans Motion with a Reeflo Dart. My return line is 1", split into two return lines 1" each, but T'ing off the return pump.

My question is what szie return pump do I need. I have a Mag 9.5 and a Mag 18. Is either close to being the correct pump? How do I measure the flow, other than by trial and error? Is there a "scientific" way to figure this out?

Thanks again for the newbie help!

[Steven Pro]

The Mag-Drive 18 would over power one 1 1/2" bulkhead. I would use the 9.5.

I don't know if there is a scientific way. I am sure there is. But, I do't know how to calculate it. But, I know I have three 1 1/2" drains and two Mag-Drive 12 return pumps, so for one hole I would use the 9.5.

[smidoid]

There IS a scientific way - yes, but you'll probably hate it unless you love math! The science is fluid dynamics (a branch of physics) and it's very, very complex with lots of big equations. http://www.fluidmech.net/

Every bend and every slope requires inserting in the equation: then there's gravity to consider, temperature, viscosity and turbulence too... It applies to lots of esoteric stuff from flight dynamics to natural gas to weather forecasting - you name it!

I prefer the suck it and see approach. Much easier! Here's a working example fresh from the picking.

My fuge is fed via two 1.5" pipes with elbows fastened on each. For convenience - the two pipes drop 1M and join via a "T" to a short length of 1.5" BUT this also causes a stricture which effectively reduces the flow. Every bend (and mine has 6 in all) slows the flow to some degree.

The return pump is rated at 1700Litres per hour max (reduced to a more realistic 1200 after the 1.5M head is added.)

The head works in the opposite direction too - causing the water to flow faster as it drops father.

The fuge buffers the overspill until it reaches equilibrium with the pump . The whole deal is adjusted (get this) by turning the elbows into the water - not my idea, but it works a treat! (The neat side effect of this is that it skims the surface water off allowing an upcurrent of "dead" water from below for gas exchange.)

The deeper the elbows sit in the water, the faster the flow and the higher the level of water in the sump; and vice-versa. Every adjustment takes about a minute to settle.

You can see from this example that I'm turning over about 1000-1200Litres per hour which is about 6-8 times my total water volume - Stephen and others will say if that's too much or to little... I'm just a hacker - and bottom line, I expect Steve's right about the 9.5!