Return Plumbing Question

[Randrew215]

I'm almost ready to kick off a build thread upgrading to a 125. One of the last things I'm trying to figure out is how to run the return plumbing. The drainage to the sump runs through a beananimal overflow in the upper left of the tank. My return pump is a mag 12. My questions are:

1. The outlet off the mag 12 is 3/4". Does it matter if I up this to 1" pvc for return? I'm sure I'll probably split the return and run at least two return lines to the display. Can I run everything at 1" pvc?

2. Should I drill for the returns or run them up and over?

3. I want to make 100% sure that the returns cannot act as a siphon in the event of a power outage/being turned off. Should I incorporate check valves or is it more a matter of running a loop of plumbing above the height of the entry point to the tank?

Please be blunt if these questions lack clarity. There's a lot of information on reefcentral about drainage, but far less discussing return plumbing. I appreciate your input!

 

[Tonynlo]

1) yes you can do that, and may have to go up to 1" depending on the answer to #2.
2) Purely your decision. I prefer everything to be drilled, and plumb clean.
3) Make sure your sump is large enough to hold all of the siphoned water and you will have nothing to worry about.

 

[der_wille_zur_macht]

Danner actually specify that 1.5" plumbing should be used with that pump:

http://www.pondmaster.com/Store/images/instructions/ZG100.pdf

It's common to use smaller sizes though and won't hurt anything other than reducing flow a bit.

I'd stay away from check valves. Use siphon break holes and/or position the plumbing such that the inlet is high enough in the water column that it doesn't siphon enough to overflow the sump. You can really do this regardless of if the plumbing is over the back or through a drilled hole.

 

[tmz]

1. Bigger is better ; you loose less flow to friction head loss. My iwaki has a 1 inch outlet . I use 2 inch pipe for returns .
2.Check valves have history of failure overtime.. I use siphon holes just below the water line in the return pipe . They may clog from time to time . Poking them back through to clear algae ,detirtus, etc. once in a while helps. Setting the return opening near the top of the water line minimizes backsiphon for returns . How are you handling the drains?
3. Siphon will climb a plumbing loop. There may be a way to use a loop of sorts with a siphon break but I don't know it.

 

[cardiffgiant]

1. I agree with others, 1.5" plumbing will greatly reduce friction and give you the best gph from the mag12. If you're going with a beananimal overflow, are you also using 1.5" plumbing to the sump?

2. If limited sump volume or corals toward the surface of the water are factors, go up and over. I come up above the top of the top of the tank with PVC, then use loc line to go over. Then...

3. ... I use the flat loc line nozzles and that are just below the surface of the water, breaking the siphon immediately when the return pump is turned off.

 

[Tonynlo]

1. Bigger is better ; you loose less flow to friction head loss. My iwaki has a 1 inch outlet . I use 2 inch pipe for returns .

Wouldn't increasing to a 2" pipe increase head loss? I can see where friction from the pipe would be reduced, but what about the weight of additional water in the pipe?

Although this is on a massive scale here, I am only using it to illustrate my point. Consider a bucket with a pump fitting on the bottom. I would think the added weight from the additional water volume (beyond the recommended outlet nozzle size) would increase head loss. In this case, we are looking at a 12" bucket and not a 2" piece of PVC.

no?

 

[Haffs09]

Here are a couple good references to review:

http://www.advancedaquarist.com/2003/1/aafeature2

http://www.advancedaquarist.com/2007/5/aafeature2

If you download the Pump Head Loss Calculator in the second link, you can play around with different plumbing sizes and see the end result (flow rate, velocity, total dynamic head). Plumbing 1.5" supply line is probably your best option (to maximize flow). Anything over that really doesn't help much.

There are losses due to rapid expansion in pipes. What the contributions are off hand, I don't know. In your example with an extreme expansion, the pump will likely operate at its max gph because it is essentially at 0' head. The water will just circulate within the pipe rather than flow anywhere. As your pipe diameter increases, your output velocity decreases. At some point, the velocity will be zero which equates to zero flow at the output.

For returns to the tank, I always drill an 1/8" anti-syphon hole in the bottom of the returns (angled into the tank), just above or below the display tank water level. That has worked well for me.

 

[der_wille_zur_macht]

Centrifugal pumps work by creating pressure. The amount of water they can move through a given system is based on the pressure the pump creates vs. the pressure of the system, which is comprised of static head pressure (feet that the pump is lifting water) and friction loss (at the operating flow rate).

Wouldn't increasing to a 2" pipe increase head loss? I can see where friction from the pipe would be reduced, but what about the weight of additional water in the pipe?

When we're talking head, we're talking pressure. Pressure 1' under the surface of the ocean is the same as pressure 1' down in a 1" diameter pipe. This is because pressure is a measure of force per unit of area - weight doesn't come in to play. Weight depends on height AND cross-sectional area and since pressure is a measure of force (weight) per unit area we're cancelling that out. A 1" pipe will hold a smaller weight of water than a 2" pipe for a given height but the pressure will be the same.

Although this is on a massive scale here, I am only using it to illustrate my point. Consider a bucket with a pump fitting on the bottom. I would think the added weight from the additional water volume (beyond the recommended outlet nozzle size) would increase head loss. In this case, we are looking at a 12" bucket and not a 2" piece of PVC.

The extreme mismatch between pump outlet and "pipe" size in that example makes the whole argument meaningless since you're introducing all sorts of exceptional factors.

Back to our aquarium example. Though the static head pressure will be the same for 1" pipe as for 2" pipe, the performance of any pump, in terms of GPH, will be better in the 2" pipe. This is because there's less friction loss. In the pumps we're normally using, this is a significant difference. Going from 1" pipe to 2" pipe on a given pump might be a 100% increase in flow rate.

The hangup for most people to understand this is often that they're thinking in terms of velocity (i.e. feet per second) not rate (gallons per hour). It's very true that a larger pipe diameter will mean a lower flow velocity, and in our head, it's easy to think this means the pump is moving less water since the water is moving more slowly. But in reality, it's moving more water since the friction loss is lower.

 

[tmz]

^^^ +1
The stream of water from the pump flows through the surrounding water on the edges as a means to reduce friction headloss. As the pressure increases in the pipe it increases in the whole pipe up to the outlet which is usually smaller when a larger transport pipe is used.

 

[Randrew215]

Thank you everyone for the thoughts! I think that I will run 1.5" pvc from the pump and take it up and over the tank. No check valve. I like the idea of having a siphon hole just below the water line or the idea of having the nozzle outlets just below the water line to minimize water siphoned to the sump.

This has been an amazing learning resource for me and I'm looking forward to putting up a build thread with lots of pictures. It will probably be next month.

 

[tmz]

Good luck . Looking forward to your build.

 

[jacksonpt]

Just don't RELY on the siphon break hole(s). Designing your sump/plumbing to handle the backflow is the far and away the best option. If you're going up and over with the plumbing, just don't submerge the outlets very deep.