Head Loss - Am I missing something?

TeapotMaster

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Hello all,

New reefer here, with a recently post-cycled tank.

My first couple of weeks were spent trying to figure out equipment specs. One of the main ones I was trying to dial in was finding the right return pump that would fit in my pump and deliver the right turnover to my 48 gal tank. I went by the rules of thumb to calculate head loss -- to each foot of vertical height, add 1ft for 90 degree elbows, for every 10ft of pipe, so forth an so on. In my case, I have a bit over 3 ft of vertical rise, four 90 degree turns, for a total of approx. 8 ft of head. Based on this info, I purchased a Varios2 which, based on published info, delivers at max speed ~250 gph at 8ft of head pressure. A little over 5x turnover, should do the trick if cranked full.

Then, I decided to ask my handy dandy AI for some help, which suggested I only had about 3.4 feet of head, since rule of thumb of 1ft per 90 degree elbow is bunk. Based on this, it estimated that i should be able to hit 10x turnover at speed 3 on the pump. No way, I said. So, I chopped up my plumbing to fit a tee at the top of one of the return lines and ran a hose for a bucket test.

Lo and behold, at speed 3, I am cranking out ~470 gph. Tested it several times with consistent results.

So, although I am absolutely stoked about the pump I bought (I could not hear it operating inside a monastery while wearing a stethoscope) I clearly spent a bit extra on an overpowered pump, when a much smaller Sicce silent would have done the trick.

The question is, am I missing something? Based on the above, the "rule of thumb" estimated double the true head pressure for my system. That's nowhere close. And if I am not missing anything, why are we still citing a rule of thumb that is in no way an approximation of reality?
 

Stakenshake

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Was the bucket on the floor? If so you then changed the entire head curve of the system when you lowered the hose down to the bucket

The 1’ per elbow is quite a bit conservative. The best book for for reference on easily calculating head loss is Cameron’s hydraulic data. You can find pdf copies online.
 
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TeapotMaster

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Was the bucket on the floor? If so you then changed the entire head curve of the system when you lowered the hose down to the bucket

The 1’ per elbow is quite a bit conservative. The best book for for reference on easily calculating head loss is Cameron’s hydraulic data. You can find pdf copies online.
My goodness, what a goof. I didn't even think about bucket height. Blame it on no coffee. Will redo and report back.
 

Pod_01

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Just from my experience, based on observations not actual measurements… All DC pumps that I used (Vectra S1/ Maxspect - Jump, Innovative Marine -MigtyJet ) tend to loose strength over time, frequent cleaning helps but from my observation there is a drop over time. So extra capacity is nice and all I care about is that the water keeps moving.

I tried all types of AC return pumps and regardless of claim they all hum (only the tiny ones can be considered silent), I can hear them and my wife can really hear them (her comment “What is with the train?”) so they are not a good option for my house. No noise or hum issue with any of the DC pumps that I used so far.

Good luck,
 

Stakenshake

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Just from my experience, based on observations not actual measurements… All DC pumps that I used (Vectra S1/ Maxspect - Jump, Innovative Marine -MigtyJet ) tend to loose strength over time, frequent cleaning helps but from my observation there is a drop over time. So extra capacity is nice and all I care about is that the water keeps moving.

I tried all types of AC return pumps and regardless of claim they all hum (only the tiny ones can be considered silent), I can hear them and my wife can really hear them (her comment “What is with the train?”) so they are not a good option for my house. No noise or hum issue with any of the DC pumps that I used so far.

Good luck,
The pump itself does not lose power. The root cause of the your observation could be:

the system curve changes with increased losses in piping due to muck and biofilm

the impeller gets full of muck and scum and looses performance

tolerances inside the pump get worn creating more internal recirculation.

Among others.
 

Shirak

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You put the T at the top of the return line where it enters back into the tank? Then the bucket on the floor doesn't matter. Pipe diameter will affect flow too and the number of 90 bends estimate is just a guess IMO. Better to have a pump that is double what you need and slow it down or put a gate valve on the return line near the sump so you can restrict it to get the flow you want. That way you have the ability to turn it up as needed.
 

BeanAnimal

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You have two threads going. From the other:

A few things.

First, rules of thumb are just that. Velocity is one variable among many. Wall smoothness, pipe diameter, fittings, layout, and other factors all play into the fluid dynamics and total head loss. Rules of thumb get you in the ballpark in many situations, and they exist because the actual math has too many variables for the average, or even above average, reefer to apply for a better answer.

With DC speed controlled hobby pumps, you almost always want to buy oversized, often significantly oversized. The speed control circuits are built with marginally spec’d electronic components that will live a much longer life when run at lower power.

So, buy big and run at 75% or less and the pump will almost always outlive the same DC pump run at 100%.
 

BeanAnimal

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tend to loose strength over time, frequent cleaning helps but from my observation there is a drop over time. So extra capacity is nice and all I care about is that the water keeps moving.

Motor's don't "lose power" over time so any loss is maintenance related.
 
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TeapotMaster

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You have two threads going. From the other:

A few things.

First, rules of thumb are just that. Velocity is one variable among many. Wall smoothness, pipe diameter, fittings, layout, and other factors all play into the fluid dynamics and total head loss. Rules of thumb get you in the ballpark in many situations, and they exist because the actual math has too many variables for the average, or even above average, reefer to apply for a better answer.

With DC speed controlled hobby pumps, you almost always want to buy oversized, often significantly oversized. The speed control circuits are built with marginally spec’d electronic components that will live a much longer life when run at lower power.

So, buy big and run at 75% or less and the pump will almost always outlive the same DC pump run at 100%.
Thanks! Not sure how that happened.
Was the bucket on the floor? If so you then changed the entire head curve of the system when you lowered the hose down to the bucket

The 1’ per elbow is quite a bit conservative. The best book for for reference on easily calculating head loss is Cameron’s hydraulic data. You can find pdf copies online.
Re-ran the test 4 times, this time with bucket at discharge height. A noticeable drop in flow, but now testing closer to what the pump curve shows at my head pressure of 3-4 ft (~300GPH).
 

X-37B

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Thanks! Not sure how that happened.

Re-ran the test 4 times, this time with bucket at discharge height. A noticeable drop in flow, but now testing closer to what the pump curve shows at my head pressure of 3-4 ft (~300GPH).
Overthinking return flow will drive you crazy.
300gph is fine for a 50g system.
You only need 2-3× turnover.
I run all ac returns except in
my 112 I use the maxijet dc, it came with. Way oversized for a 112 but I run it on level 2. This is the first dc return pump I have ever ran.
20260614_071857.jpg
20260614_071849.jpg
n
 

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