Opinions on using 1/2" drains with Bean Animal overflow

[trustychords]

I recently purchased a Marine Modular 800gph overflow box (top-view of outer box pictured below). It has three 1/2" drain holes that fit 1/2" uniseals. I will these for a bean animal overflow on a 32g display and a 20g sump.

I realize now, however, that the 1/2" drain holes are considered small and most folks use either 3/4" or 1". The reasoning is that larger diameter pipes can handle more flow and in the case of a blockage, could easily accommodate the blocked pipe(s). So that lead me to three possible actions:

1. Use a bushing to convert the 1/2" male thread uniseal to a 3/4" or 1" pipe. This seems like a good option, although, is it true that the smallest connection determines the maximum flow rate? If that is true, having a larger diameter pipe after the 1/2" uniseal won't matter because the maximum flow is determined by the smallest connection.
2. Drill bigger holes in the overflow box. I would like to avoid doing this as I don't have enough equipment or experience to drill acrylic. Modular Marine could have drilled 3/4" holes if I requested, but I didn't catch that detail when ordering. It also makes me think "why would the default be 1/2" holes if no one actually uses 1/2" drain lines?" The overflow box is pretty small and tight, and I assume that 1/2" plumbing provides more space.
3. Use the 1/2" drains.

With regards to the last point, the concern is that the 1/2" drains might not be able to handle the overflow in the case of a blockage. In a scenario where there is a 100% block in 2 of 3 drain pipes, that would leave a single 1/2" pipe to handle the overflow. There are two sources that I found that discuss how flow much a gravity-fed pipe can handle. One is from a reefquarium.com article and suggests that a 1/2" pipe can handle 200gph (chart pasted below). Another is from flexpvc.com and suggests that it can handle 420gph (chart pasted below) .

My return pump will be pumping less than 400gph and more likely in the 200gph-300gph range (this would still give me 10x sump-turnover per hour). This is above the reefaquarium limit but below the flexpvc limit. I know the common advice is "bigger is better" when discussing overflow pipes, but I wonder if that advice is too conservative given the bean animal overflow setup. That is, it is unlikely that 2 pipes would be 100% blocked (although certainly possible). I suppose the safest option if going with 1/2" pipes is to ensure that the 3rd pipe (i.e., emergency overflow) can handle the return pump's flow.

 

[Peace River]

If you have an overflow rated at 800 with an emergency drain and a return pump running at 200 then it seems like you are covered both for normal use and for potential blockages. Are you questioning the ratings?

 

[trustychords]

Ideally I would like to have more than 200gph flow if needed. Based on the reefaquarium article, that would be dangerous as it suggests that a 1/2" gravity-driven drain pipe can only handle 200gph.

I was hoping that using a bushing to increase the 1/2" uniseal drain to 3/4" or 1" pipe would give me some wiggle room, but I can't find a source to confirm or deny this.

In retrospect, I should have went with 3/4" uniseals. It is strange the default for the 800gph Modular Marine overflow box is 1/2".

 

[Peace River]

The MM with (3) 3/4” drains is rated at 1200, in contrast to the 800 with (3) 1/2” drains.

Another thought to consider is that for the standard configuration of a bean animal a valve is added to the primary drain line to control the water level in the overflow which in many cases will constrict the flow further. However, you will have additional drainage from the secondary (albeit not the full amount because that will be a spill drain, not a full siphon). I have to imagine this was all taken into consideration when MM rated their overflows at 800 gph, 1200, 1600, etc. If you aren’t comfortable with the ratings then it may be worth pursuing the upgrade to the 1200.

 

[madweazl]

200gph is 6.5x turnover through the sump which is more than enough. The 1/2" line should flow well over 200gph under siphon.

 

[sharpimage]

I would assume MM is smarter than me. Their 800 gph should run 800 gph at full syphon with a trickle in the overflow and the emergency dry.

 

[lpsouth1978]

I recently purchased a Marine Modular 800gph overflow box (top-view of outer box pictured below). It has three 1/2" drain holes that fit 1/2" uniseals. I will these for a bean animal overflow on a 32g display and a 20g sump.

I realize now, however, that the 1/2" drain holes are considered small and most folks use either 3/4" or 1". The reasoning is that larger diameter pipes can handle more flow and in the case of a blockage, could easily accommodate the blocked pipe(s). So that lead me to three possible actions:

1. Use a bushing to convert the 1/2" male thread uniseal to a 3/4" or 1" pipe. This seems like a good option, although, is it true that the smallest connection determines the maximum flow rate? If that is true, having a larger diameter pipe after the 1/2" uniseal won't matter because the maximum flow is determined by the smallest connection.
2. Drill bigger holes in the overflow box. I would like to avoid doing this as I don't have enough equipment or experience to drill acrylic. Modular Marine could have drilled 3/4" holes if I requested, but I didn't catch that detail when ordering. It also makes me think "why would the default be 1/2" holes if no one actually uses 1/2" drain lines?" The overflow box is pretty small and tight, and I assume that 1/2" plumbing provides more space.
3. Use the 1/2" drains.

With regards to the last point, the concern is that the 1/2" drains might not be able to handle the overflow in the case of a blockage. In a scenario where there is a 100% block in 2 of 3 drain pipes, that would leave a single 1/2" pipe to handle the overflow. There are two sources that I found that discuss how flow much a gravity-fed pipe can handle. One is from a reefquarium.com article and suggests that a 1/2" pipe can handle 200gph (chart pasted below). Another is from flexpvc.com and suggests that it can handle 420gph (chart pasted below) .

My return pump will be pumping less than 400gph and more likely in the 200gph-300gph range (this would still give me 10x sump-turnover per hour). This is above the reefaquarium limit but below the flexpvc limit. I know the common advice is "bigger is better" when discussing overflow pipes, but I wonder if that advice is too conservative given the bean animal overflow setup. That is, it is unlikely that 2 pipes would be 100% blocked (although certainly possible). I suppose the safest option if going with 1/2" pipes is to ensure that the 3rd pipe (i.e., emergency overflow) can handle the return pump's flow.

Hopefully someone with a bit more expertise will chime in, but my understanding is that the above chart does not take into consideration the fact that you will be running a full siphon. 1/2" should be capable of handling well above 200gph under full siphon.

 

[trustychords]

I am going to the worst-case scenario where 2 pipes have failed and only 1 pipe is able to drain (does this ever happen?). In that scenario, having a 1/2" pipe is much less desirable. This is based on the assumption that having the 3rd pipe is to handle to overflow in the case where the other 2 pipes fail.

I agree under full siphon that the 1/2" pipe can handle more than 200gph.

 

[madweazl]

In three years and eight months of running my beananimal setup, I've yet to have any line fail. I've had to tune it a number of times (10 or so) as gunk grew in there and I've even cleaned the primary a few times but I've never had the emergency activate or the secondary remain under full siphon for more than a couple of seconds to flush the overflow box.

 

[lpsouth1978]

I feel like it is HIGHLY unlikely that both the primary AND secondary become completely blocked. I have never even had one drain fail, let alone 2.

 

[trustychords]

I agree it seems very unlikely for two pipes to completely fail. Still, I think it makes sense to have the default be 3/4" pipes rather than 1/2".

On the other hand, it is marketed as a low-profile overflow, so having smaller pipes is part of that aesthetic. Perhaps the smaller pipes make it easier to clean and allows for marginally more water movement in the overflow box (and less likely for dead spots).