How to calculate overflow rate.

[ca1ore]

Interesting that they 'assign' the larger diameter drain as the primary. Is the drain system setup to be a siphon I wonder? At a drop of 48" (?), the 1" drain configured as a siphon will certainly move 1,400.

 

[Joe Batt]

They have an adjustment valve on the downflow to restrict it, so you can reduce the flow

 

[Cody @ChaosAq]

Great minds think alike.

I absolutely loved that back and forth between yall. I could visualize keyboards typing furiously and searching for answers

 

[CMO]

With a varios 8 (rated at 2700 gph) on a similar tank that ultimately reduces to 25mm return lines (I run 1" through my manifold but am forced to 25mm through bulkhead), I only get about 800 gph measured by Neptune flow meter through the return (manifold all closed). Additional head loss caused by the small return size seems to be quite significant based on my results.

 

[Joe Batt]

I have very similar results with the Varios 8 in my Reefer 350.

 

[Porpoise Hork]

I disagree. The downflow to the sump will have to depend on the size of the pipe returning to the sump plus the pressure / height of the water. So long as the return pump is less than the maximum downflow and I can tune the downflow down to match the return pump I am sorted.

If I have a 3000 gph pump and a downflow that can only cope with 2000 gph then I have to reduce the pump to meet the downflow maximum or I will flood the house. If I have a 500 gph pump and a downflow that can cope with 2000gph I will have no problem.

With the 650 the display size is 140g so I need a downflow that can at least cope with 10x 140gph... ie 1400gph +/- . The downflow has a fixed maximum on the Red Sea 650 Peninsula because its an off the shelf tank. The downflow can be tuned downwards, so as long as its rated at a maximum of 1400gph (ish +/-) or more, I can work with it by sizing my return pump. If its maximum is 500gph, for example, then I cant.

This is why I am trying to find the maximum that the RS 650 Peninsula downflow can handle.

One thing to keep in mind, just because a pump is rated for say 3K GPH does not mean you will get that out of it once it is all setup. First off the advertised flow rate is generally taken at the outlet of the pump. This drops significantly when you factor in the size of pipe plumbed in, length of the total pipe run, and distance of elevation from the pump to the returns. The maximum flow rate of a given system is determined by the smallest component. So you have a pump that is rated for 3K gph, and plumb in 1" ID line with a total length of 4" and a 36" rise above the pump. The maximum you will ever see is 960gph out of it no matter what you turn the pump up to. What will increase is the pressure on the system. For the drain side the general rule is to match the maximum flow rate of the return, so 1" will be all that's needed for the primary drain. The 2nd and 3rd (if equipped) are there as backups in case the primary line gets clogged. Bottom line is if you need a total turnover rate that is higher than 960gph then you will need to increase the ID size of all the plumbing to 1.25 or 1.5" and then throttle the total turnover via the pump output provided it's a DC pump and return valving.

 

[K7BMG]

I know old thread here.
This is a simple rule.

Your drain, and, WEIR what ever term you want to call them, must be able to handle more volume than the maximum your pump can put out into the tank period, if not you WILL overflow your tank.

The drains can move a lot of water but the calculation method needs to be based on syphon calcs, not a pump and preasure calc, pumps and preasure can push more water through, than a syphon will draw in most cases. Sure If you had a 100 foot tall syphon line, the gravity of the water will raise the syphon GPH dramatically. Also the head pressure will bave an effect, we have all seen this when we drain our tanks, full tank, the syphon rips and as the water level reduces so does the output volume of the syphon.

I dont know about all of you but I do not ever want to overflow my tank, so personally I want the drain system to be able to handle 30% more volume than my pump could ever produce, this allows for a small marging of error for debris buildup or other ways the drain can get clogged up.

Currently my new set up has a inadequate factory installed weir and drain setup. FOR MY NEEDS.

I have a Varios 8 using 1-1/4 line and a flow meter.
I have two 1 inch full syphons, and about 20 inches of weir.
My Varios 8 according to my flow meter at full output can push 1450gph.
Yea..........well not so fast, once it hit my weir and drain they quickly were overwhelmed with that much volume. I had to step down the Varios to 3 at 1100 GPH. So thats the max my drain system can do. Thats clean with no debris or other obstruction. That my reefing friends is no good in anyway.

So I have a real problem, if a power outage or some other anomaly occurs and my controler gets set to full output. Water on the floor.

So at 1100gph the two 1 inch drains easily keep up but my weir is being overrun, so I need to address that first, I have a couple of options I am considdering. From that step I need to know how much the two 1 inch drains will actually handle once they get enough water feeding them through the weir.

I am thinking maybe I picked the wrong tank. I questiond the return design right off but I got such an exelent price, as this was a special order tank, and the original buyer for what ever reason did not pick it up, and forfeited the down payment, that the dealer applied to my bennifit.
So I got a brand new calculated out 137G six foot tank with starfire glass braced for less than half the cost for $500.00.

 

[RubyU235]

you have it totally opposite. you start with pump and then see what gph is being delivered after head loss. then you make sure the drain is a size up than what pump can push. water drain with gravity not with pressure.
down will always be dependent on the pump pushing up given all pipe sizes are according.
i already mentioned the sizes of pvs with their natural flow under gravity. you can go from there.
what size bulkhead is on the down/drain of the tank?

I just wanted to give some perspective. It’s a feedback loop. Think of it in terms of if this then that.

If no water is being being pumped, no water will return.

If water is being pumped, water will return.

The amount pumped and returned are related but depend on 3 factors.

Sump side to display side:
Inlet Pump throughput.
Inlet Pipe throughput.

Display side to pump side:
Outlet pipe diameter.

And both share considerations for run length, angles, and flow path.

So unless you wanted to get super mathematical, the best and most practical approach is to generalize.

We know we can’t return more than what the pump can process. Work back from there, subtracting percentages of flow to approximate. That or get a small CFM meter I guess and measure it directly.

Honestly, just looking at it from the point of restriction and capacity gives you a good idea of what constraints you have.