Plumbing pipe size calculation

[Reef_Hobbyist]

Is there a calculation that can be used to properly size loc lines on a pump return?

I have a closed loop with a Blueline HD 70 pump and 1" PVC. I am thinking about using (4) 1/2" loc lines on the return. Is there a way to calculate how much loc line should be used to provide maximum GPH? What if 3/4" loc line was used?

I am also curious about what size nozzles to use (1/2" or 3/8") and how that affects both GPH and the speed of the flow. I would think the 3/8 nozzle on a 1/2 loc line will generate a faster flow speed but will increase head pressure and thus reduce gph to some extent unless there are enough loc lines?

 

[Reef_Hobbyist]

I believe these are the specs of the components and I think I am going to go with (4) 1/2" loc lines. It would be great if there was a formula to guide us on this.

• Blueline HD 70: 1,750 gph max
• 1” PVC: 2,200 gph w/ med psi
• Loc-Line 1/2" ID: 20-30 PSI - Flow Rate: 478 gph
• Loc-Line 3/4" ID: 10-20 PSI - Flow Rate: 1,140 gph

 

[Jlobes]

I was just thinking about this the other day, albeit not for a closed loop, but for my returns. I was pondering if I should swap out the 3/4" Y and fittings, for a 3/4">1/2" Y and use 1/2"a locline fittings. I made the same assumption, that using a smaller diameter would have increased "velocity".

I think @AZDesertRat might be able to help us out. anybody have any info on this?

 

[bct15]

Using smaller diameter anything will increase the head loss and reduce your gph. (Assuming the same flowrate) The water coming out the smaller nozzle will be traveling a little bit faster than the wider nozzle, but in real world the large reduction in cross sectional area and increased head pressure will result in a substantially less total gph and possibly even less velocity due to the pressure loss since you're providing the same pressure at the pump regardless of nozzle size.

 

[Reef_Hobbyist]

Using smaller diameter anything will increase the head loss and reduce your gph. (Assuming the same flowrate) The water coming out the smaller nozzle will be traveling a little bit faster than the wider nozzle, but in real world the large reduction in cross sectional area and increased head pressure will result in a substantially less total gph and possibly even less velocity due to the pressure loss since you're providing the same pressure at the pump regardless of nozzle size.

Exactly so I am wondering if there is a calculation to help select the number of loc lines, their size and their nozzle size to achieve max velocity out of each nozzle without reducing overall gph. I'm guessing too few loc lines would reduce overall gph and too many would reduce velocity at each nozzle?

 

[bct15]

You could use a standard fluid formula and assume the head loss coefficient for the loclines...maybe treat them like a nozzle or a reducer and an elbow.

Or you could hook your lock line up to your pump then full a five gallon bucket with it, which you could time how long it takes to fill the bucket to get your gph. You could then use your loss of flow rate to get your head loss coefficient for the locline, using the basic fluids formula and solving for the K value. Then you could plug it in to your entire circuit (multiple loc lines) in the fluids formula to get the gph through each nozzle.

I can tell you each loc line you add will reduce your total gph, due to head loss from the additional pipe, fittings, and loc line. The smaller the pipe/loc line the more it will reduce your flow.

 

[AllSignsPointToFish]

Okay, so I did some calculations on this topic to give an idea of the effect of pipe diameter on pressure drop. There is more than one way to skin a cat, so I ran the same simulation with varying schedule 40 PVC pipe diameters. I assumed water at 76°F flowing through a 6' section pipe oriented vertically in the air. I assume the discharge of the pipe was at 0.1 psig, or 2.77 in water column. The flow was assumed to be 1200 GPH. Here are the results:

Size (nom.) Pressure Drop (psi) Velocity (ft/s)
3/4" 4.20 12.03
1" 3.09 7.43
1 1/4" 2.73 4.29
1 1/2" 2.66 3.15

As you can see, velocity varies with pressure drop. I did not add any fittings to complicate the analysis. Hopefully, this information is interesting if not of some actual use to folks.

 

[AllSignsPointToFish]

As far as Loc Lines go, I would consider them similar to corrugated stainless steel hoses used for materials transfers (albeit maybe not as bad). Basically, from the literature I've read, you can assume that a hose has twice the pressure drop of a piece of piping the same length. Given the manner in which the Loc Lines are designed and in the absence of actual data, I would treat the Loc Line as if it were a piece of straight pipe twice as long when performed fluid flow estimates.

 

[AllSignsPointToFish]

Here is the data in a better format:

 

[bct15]

Okay, so I did some calculations on this topic to give an idea of the effect of pipe diameter on pressure drop. There is more than one way to skin a cat, so I ran the same simulation with varying schedule 40 PVC pipe diameters. I assumed water at 76°F flowing through a 6' section pipe oriented vertically in the air. I assume the discharge of the pipe was at 0.1 psig, or 2.77 in water column. The flow was assumed to be 1200 GPH. Here are the results:

Size (nom.) Pressure Drop (psi) Velocity (ft/s)
3/4" 4.20 12.03
1" 3.09 7.43
1 1/4" 2.73 4.29
1 1/2" 2.66 3.15

As you can see, velocity varies with pressure drop. I did not add any fittings to complicate the analysis. Hopefully, this information is interesting if not of some actual use to folks.

I think what he wants is the opposite calculation, assume you have the same pump on all of your inlets and calculate the velocity at the outlet.

So you'll start with the same pressure at the bottom of the pipe and calculate flowrate out (in gph), using different diameter pipes.

The calculations you did show a pressure drop and assume the pump at the inlet is adjusted to maintain the same flow rate.

 

[AllSignsPointToFish]

Yes, you are correct. However, I don't have specific pump information, but I could estimate a typical return flow rate to show the effects of pipe diameter on velocity and pressure drop at a constant flow rate. I could do the analysis you described if I had a pump performance curve for reference.

If I were to know maximum pump discharge pressure at deadhead conditions, I could vary the flow rate instead.

 

[bct15]

The issue with your calculations is that you're using a constant flow rate and not accounting for the flow loss due to pressure drop. The fluid velocity is simply a function of the cross sectional area and the volumetric flow rate.

velocity = flow rate/area

Your outlet velocity can drop due to the drop in flow rate, even through a smaller nozzle. For example;

Assume you have a pump that provides 500 gph through 4 3/4" loc lines. The total area cross sectional area (pi*r^2) of those loc lines is around 1.76 in^2. The flow rate converted to in^3/sec is about 32 in^3/sec. Dividing that gives you an exit velocity of about 18.25 in/sec.

Now assume the same pump gives you a flow rate of 200 gph through 4 1/2" loc lines. The total area of the exits of the loc lines is about 0.8 in^2. 200 gph is around 12.8 in^3/sec. The exit velocity at each loc line is then about 16 in/sec.

So the loss in flow rate gives less flow and a slower velocity at the outlets. Of course this assumes uniform flow, and ignores the viscosity of the fluid.

 

[Rjramos]

I believe these are the specs of the components and I think I am going to go with (4) 1/2" loc lines. It would be great if there was a formula to guide us on this.

• Blueline HD 70: 1,750 gph max
• 1” PVC: 2,200 gph w/ med psi
• Loc-Line 1/2" ID: 20-30 PSI - Flow Rate: 478 gph
• Loc-Line 3/4" ID: 10-20 PSI - Flow Rate: 1,140 gph

Thanks for this info I just hooked up a 180gal with Blueline 100, running skimmer off it and have 4- 3/4" loc-line. Outlets from 3/4" overflow box riser. I don't have the pressure I was looking for on the 3/4" so gonna reduce everything to 1/2"

 

[AllSignsPointToFish]

The issue with your calculations is that you're using a constant flow rate and not accounting for the flow loss due to pressure drop. The fluid velocity is simply a function of the cross sectional area and the volumetric flow rate.

velocity = flow rate/area

Your outlet velocity can drop due to the drop in flow rate, even through a smaller nozzle. For example;

Assume you have a pump that provides 500 gph through 4 3/4" loc lines. The total area cross sectional area (pi*r^2) of those loc lines is around 1.76 in^2. The flow rate converted to in^3/sec is about 32 in^3/sec. Dividing that gives you an exit velocity of about 18.25 in/sec.

Now assume the same pump gives you a flow rate of 200 gph through 4 1/2" loc lines. The total area of the exits of the loc lines is about 0.8 in^2. 200 gph is around 12.8 in^3/sec. The exit velocity at each loc line is then about 16 in/sec.

So the loss in flow rate gives less flow and a slower velocity at the outlets. Of course this assumes uniform flow, and ignores the viscosity of the fluid.

Your comment assumes a pump performance curve with a fair amount of curvature to it, which is not always the case. Some pumps exhibit more linear characteristic curves and show little drop in head as flow increases which is why it's important to have the actual curve.

 

[Reef_Hobbyist]

There must be a calculation that can help us figure out how to plumb our systems in a way that provides the best gph and flow velocity by selecting the right pump, pvc diameter and loc lines (quantity, diameter and nozzles).

I installed my closed loop pumps on a shelf up close to the bottom of the tank where I can have the shortest run to the bulkheads (1" pvc with less than 2 feet run) and the fewest number of elbows (2). Now I am curious how many loc lines, the diameter of loc lines (3/4" or 1/2") and nozzle size (3/4"or 1/2").

 

[AllSignsPointToFish]

What pump did you install?

With a little more information, I can actually probably model this for you and let you know for sure. What does the installation look like on the other side of the bulkhead?

 

[AllSignsPointToFish]

I would guess that's a Blue Line Aqua 70HD, no?

 

[AZDesertRat]

I would opt for maximum flow or GPD versus velocity. You want turnover not a jetting action or pencil stream. Necking it down to increase the velocity really adds head to the pump and a loss of flow.
I had a closed loop on my current system when I built it 13 years ago and used a Quiet One 4000 rated at 1000+/- GPH through 1" suction and discharge into two 3/4" Loc Lines back to the display. It was OK but nothing spectacular so I tried adding a SCWD switching device which was a little better since it directed all the flow first from one then from the other nozzle so velocity was a little better. The problems though were the SCWD had so much headloss turning all the little gears and turbine it robbed 25-30% of the flow and it required constant cleaning and soaking in vinegar to keep it operable.
I switched to an Oceans Motions Squirt two way which was a huge improvement since it was electrically operated and did not have anywhere near the headloss so the velocity was awesome. The problems here though was the Quiet One 4000 was an absolute point of sale and ran hotter than blazes until it literally burned up, sparks, flames and all. The other was the constant 58 watts to get 900-1000 or so GPH and the associated heat gain in a 100G system in Phoenix in the summer. My 1/4HP chiller ran a good part of the day and night and added a good bit to my electric bill.
I eventually ditched the closed loop all together and went with powerheads or wavemakers. I tried the modded MJ1200's and wasn't at all happy with them since they were huge, still used suction cups and rattled a lot. They did provide some flow though. I next tried two Sicce Voyagers and again they were huge and ugly in a 5 foot 100G reef system. Power consumption was still pretty high and they were kind of noisy. Next up was Seios which were a big improvement and used for quite a while before switching to Hydor Koralias at about 8 watts for something like 1600 GPH each. I added a Reefkeeper Lite about the same time and put them on a wavemaker function and they held up pretty good to the constant switching after the free manufacturer upgraded covers were put on. After something like 2 years and 2 million starts and stops I switched to the current Hydor WP-25's I still have today, get much more flow and random patterns and only about 16 measured watts at high speed for something like 4000+ GPH and they are not much bigger than a golf ball in size.
The closed loop was a good idea before the advent of todays wavemakers but I don't think I would go that route again. I did repurpose the Oceans Motions Squirt on my sump return line so get additional switching action without having to add an additional pump and heat load.

 

[Jlobes]

well, like I said, AZ should be able to shed some light!

 

[AZDesertRat]

One of the absolute best investments I have made in this hobby is a couple of Kill A Watt meters. Being able to monitor power consumption has really made my pump and lighting choices much easier. More efficient pumps, getting rid of the closed loop, ditching the chiller for properly placed fans and most of all, LED lighting with no fans versus MH and VHO saved me $60-$75 a month year round on power bills.