Max Flow Rate 3/4”

[Kyle Bruin]

So for piping a return line I’m curious if anyone can give a cursory explanation or math behind the restriction piping size can put on a pumps gph rating. I’ve been running a Neptune cor-15 on a Waterbox 130.4. At the end of the run, the flow goes through a metric 3/4” equivalent (DN25 if I’m not mistaken) to a tee and then loc line to the display. I was getting just over running from a 1-1/4” union to a 1” bushing, some 1” pipe, flow meter, and elbows, a 3/4” reducer, check valve and out. I decided I wanted to a) increase overall turn over and b) run equipment off the return pump (reactor, uv).

I reran the plumbing in 3/4” and got a similar flow rate. Basically starting with 1-1/4” and using 1” for most of the run didn’t really matter.

So now I’m trying to size a pump and curious how big I can go before the 3/4” restriction just gives diminishing returns. Can I put a varios-8 or a ETM L2 on this and get 7-800+ with a few hundred for accessories? I want about 300gph for my uv and another 1-200 for the reactor.

Basically, what’s a good strategy to try and calculate flow (via head pressure?) with a more complex setup than just straight gravity flow and 90s? If you have 3/4” return, 3/4” uv, 1/2” reactor does that help with the restriction that the 3/4” pipe puts on the rated flow?

Or another way of looking at it, does putting a successively bigger pump on the same size line eventually stop yielding higher flow? Or just inefficient? Is there a max flow for 3/4” pipe?

 

[Pete Luna]

I am no engineer, I have a 1" line on my return pump, I replaced the line going out of my UV from a 1" to a 1 1/4" line and increase my flow by 100 gph.

 

[Kyle Bruin]

Any other thoughts on plumbing size and restriction forces? Or max pump size on a 3/4” line?

 

[Crashnt24]

In curious as well. I have a 3/4" return hole in my tank and want to run 900gph. I don't know the standard water pressure these pumps put out but I found this....

 

[Kyle Bruin]

I assume pressure is related to flow rate and restriction. That chart leads me to believe you could, with the right size pump get to 900 on 3/4”. Not sure how you would approach sizing that pump, but I’m guessing you would want a very large 3000+ dc pump. Worst case is you run it well below 100%.

also, I know many sumps and mechanical filters have max gph to consider as well.

 

[DCR]

That chart is for high pressure spa's. Even the middle (yellow) range if for pumping systems with over 50 ft of head at flow. As a process engineer, I would not use 3/4" pipe for much more than 400 gph, which is probably fine for your tank. I think the COR-15 will probably work well with the other manifold loads. You can certainly get more by running your pump at high speeds, but then you negate the benefit of the DC pump. Most people on this forum vastly overestimate their return flows because of the small restricted piping that is being used. 900 gph will fill a 5 gallon bucket in 20 seconds. If you had that kind of velocity coming out of a single 3/4" return it would likely spill over the sides. I would increase the manifold to at least 1" or even 1-1/4"

 

[Kyle Bruin]

That chart is for high pressure spa's. Even the middle (yellow) range if for pumping systems with over 50 ft of head at flow. As a process engineer, I would not use 3/4" pipe for much more than 400 gph, which is probably fine for your tank. I think the COR-15 will probably work well with the other manifold loads. You can certainly get more by running your pump at high speeds, but then you negate the benefit of the DC pump. Most people on this forum vastly overestimate their return flows because of the small restricted piping that is being used. 900 gph will fill a 5 gallon bucket in 20 seconds. If you had that kind of velocity coming out of a single 3/4" return it would likely spill over the sides. I would increase the manifold to at least 1" or even 1-1/4"

So right now I get 450 with my cor-15 at 100%. No manifolds. I did briefly try a maxspect duo12k pump (just one output) and got close to 600. I think for my 130gal (100-110 actual water volume) 6x turn over is probably okay. So my goal is to just keep that 600ish rate back to the tank but with another 350 going through a uv and maybe 200 through a reactor. So that’s roughly 1200 gph if I put the flow sensor before any manifold.

you are saying that should be done in at least 1”?

 

[Kyle Bruin]

The other question is then pump size. I had been thinking a ETM vectra m2, but that’s only about 500gph more (cor-15 is 1500gph rated). If I need overall output of around 1200 gph (3/4” return -600gph, 1/2” reactor-200gph,1/2” uv-350gph) I think 2000 isn’t enough with the head pressure and pipe diameter restrictions?

maybe an L2 vectra or varios-8? Again worst case I run the pump slower?

 

[DCR]

I would be looking for a pump that can deliver your desired flow (1200 gph) at about 7-8 ft of head (not the dead head zero flow head nameplate they offer). The COR-20 would be very marginal. Varios-8 should work as well as an L2, although I hear a lot of complaints that the DC pumps do not perform up to their published performance curves. ET no longer even publishes curves for their pumps. For 1200 gph, make your manifold 1-1/4 and run at least a 1" pipe back to the tank and reduce down at the bulkhead for 600 gph . You are still going to be running your pump at near max speed.

 

[dbowman5]

my $0.02.
one consideration of flow is the pump's ability to push fluid. If you were to submerge a pump with no restrictions on intake or outflow that pump would move the fluid at a certain gph through the pump. that flow would depend upon the pump and the fluid. the thicker the fluid was the less flow that pump would deliver. ( think warm water vs maple syrup in winter)
the pump would also be a factor. some pumps have positive displacement others do not. Positive displacement means that a volume of fluid moves through the pump and then another volume equal to that moves through the pump. think of what happens if you connect a pump output to a valve. then close the valve. does the pump keep running? if it is positive displacement it will pressurize the pipe between it and the valve then either stop pumping or blow out the plumbing. if it is not a positive displacement pump it continues running but just spins the water in it until you open the valve then pumps. As pumps age the seals tend to wear out causing less flow because the water will go where it is able to not necessarily where it was designed to.
To get back to the original point, when you restrict the output by adding either smaller fittings, changes in direction, vertical distance or just distance, you create back pressure on the pump. this reduces the flow by predictable volumes. this back pressure on a positive displacement pump increases the torque on the motor making the motor work harder. AC and DC pumps handle the workload differently, like gas engines vs diesel ones.(diesels handle torque much better but gas engines get better mileage at low speed/load conditions) Also over time the actual i.d. gets smaller due to build up inside the plumbing. when i size plumbing systems i want as little pressure in the lines as possible. I want to be able to disconnect the parts for maintenance and repair. i want to use good quality components that are compatible with the rest.
for these reasons i will use i.d.'s rated for the pump. My return line starts out at 11/4" and enters the DT at 1 1/4". i have a valve that is 'Teed' and reduces to 1" for add on usage. a lot of people will split to smaller pipes downstream to maintain pressure at all outputs. the reason for a throttle valve on return lines is to give a certain flow on a new set up so that down the road as the system ages the valve can be opened to bring the flow up to that original setting. The problem with that is that you make the pump work harder and prematurely age it.
excuse me, i like posts that are short and sweet but cant always remember that. maybe i should start writing articles to chase my thinking down. I feel like the guy who is asked for change for a twenty and starts pulling out nickels and pennies.
I hear: 'Uh, never mind, I don't need it that bad.'

 

[HeyJay]

How to Estimate the Head Pressure on Your Return Pump - Simplicity Aquatics

Most pumps are listed with GPH (gallons per hour) flow rates to give you an idea of how much water they will move, however this number is with zero head pressure. In reality, most aquarium return pumps have a good amount of head pressure against them, so the flow rate at zero doesn’t necessarily...

www.simplicityaquatics.com

 

[ichthyoid]

If I understand it, the incoming hole in the tank is 3/4 inch?

If that is the case, why not just add a second 3/4 inch pipe run and hang it over the top of your aquarium? I made a similar mod to a Marineland 120 that had 1 overflow with 2 holes. I wanted the 2nd hole for a backup drain, so ran the return over the side. It worked like a champ! I got a little creative with the pvc by adding a T with a short dead end branch facing down, which helped hold it on the side of the tank.