How does the flow to/from the Sump regulate itself?

[Simon_M]

My question, is how does the flow to/from the Sump regulate itself?

I have a Red Sea Reefer 625 G2 Tank. It has a DT that is about 500 litres and a Sump that is 125 litres. I use a DC Return Pump that is rated up to 8000 lph but use it at about 60% - there are also losses from tubing and the head height to consider. The maximum flow rate for my DT and ReefMat isn't being exceeded.

I try to have the level of the Water in the Weir Box at just below the level of the Emergency Overflow. When it works, the inside of the Overflow stays dry. I don't know if this is the ideal way to operate? Also in the Weir Box is the Red Sea Down-pipe and there also two output pipes on each side, to return water to the DT.

Regulation of the flow out of the Tank is with the Red Sea Red Diaphragm Valve - it has markings around the outside and each mark varies the height in the Weir. It isn't difficult to reach a point where the height is (relatively) stable. What I find confusing, is how the System regulates the flow and stabilises the level. The Down-pipe is really two pipes with an outer pipe that has a square clear top. This sits on top of the inner pipe that is at a lower level and is centred by the first pipe. In normal operation the top of the outer Down-pipe is above the level of the Emergency Overflow - so water does not flow over the top. I assume that water in the column between the two pipes flows up and into the inner pipe. Since the outer pipe rests on the bottom of the Weir, it isn't obvious how this flow either gets through or is stable enough to be relied upon.

If the level in the DT rises and the height inthe Weir also increases, water can start to flow down the Emergency Overflow and a gurgle is heard. Only in extreme cases would it overlfow into the outer Down-pipe. If the water level is too low, then there is also a gurgle from the entrance to the Weir as Water passes though the holes and falls down.

I can regulate the flow easily enough and I can get the system stable. I use a Tunze OTA to set the water height in the Return Chamber. As Water evaporates, it replaces the lost water - this works.

My initial impression is that the water flows down the Down Pipe and the rate is limited only by what can pass through into the Weir Box. This can be varied by regulating the Diaphram valve or by changing the DC Pump speed e.g. selecting a slower/faster setting. It does seem that the Weir height is simply a balancing act between input and output - so how does it regulate? Changes in the height of the water in the Return Chamber also seem to influence (a little) the performance.

If I simulate the evaporation of water in the DT by removing a litre of water the System doesn't always adjust so the height could stay at this level, increase or decrease. I'm sure that the detail varies across different Weir Box designs, but that same principle of operation is being used? Some Users will allow a small flow of water to always pass down the Emergency Overflow - perhaps this is how they regulate the height. To me this seems like the operation of a fault WC, only by using the WC Overflow is the height in the Cistern Maintained.

 

[topjimmy]

My over flow box is always full. If you're having issues I'm guessing you need to add more water. There should not be any rise and fall as the return pump fills the tank until it hits the over flow.

 

[RocketEngineer]

Overflow 101: The amount of water leaving the tank equals the amount of water entering the tank. What varies is where the water goes. Assuming no evaporation has occurred, the following details what’s happening in the wier.

After looking at the drains, what you have is known as a Herbie system. The main drain pipe is a siphon that gets restricted by the valve in order to flow as close to the pump rate as possible. If the pump is a tiny bit behind the siphon, the water level in the weir decreases a fraction, thus reducing the pressure into the siphon and slowing it a fraction. If the pump is a tiny bit faster, the reverse happens and the siphon speeds up to balance.

Now, if something goes way off, the siphon runs too fast and the siphon pulls air, making noise. Or, the siphon gets plugged, the water level in the weir rises, and eventually the emergency drain starts flowing, making noise and letting you know the main drain is not working correctly.

Once the drains are set, the only real change that should be seen is evaporation. That should show up in the return pump section and the ATO handles that.

Hope that explains things.

 

[Simon_M]

My over flow box is always full. If you're having issues I'm guessing you need to add more water. There should not be any rise and fall as the return pump fills the tank until it hits the over flow.

I have the weir (overflow) box at the height that is just below the (emergency) over flow pipe. I was aiming for no water to normally flow through the over flow pipe - except if the main drain becomes blocked.

Some Users aim to have a trickle of water always passing though the pipe, with the aim of having the flow increase if the weir was to over fill but without the need to (exactly) balance the input and output.

I was trying to avoid any normal flow in the pipe because it would a) keep it clean and b) all water would pass through my ReefMat. It is also the method Red Sea show in their HowTo maintain the Diaphragm Valve video.

 

[Simon_M]

Overflow 101: The amount of water leaving the tank equals the amount of water entering the tank. What varies is where the water goes. Assuming no evaporation has occurred, the following details what’s happening in the wier.

After looking at the drains, what you have is known as a Herbie system. The main drain pipe is a siphon that gets restricted by the valve in order to flow as close to the pump rate as possible. If the pump is a tiny bit behind the siphon, the water level in the weir decreases a fraction, thus reducing the pressure into the siphon and slowing it a fraction. If the pump is a tiny bit faster, the reverse happens and the siphon speeds up to balance.

Now, if something goes way off, the siphon runs too fast and the siphon pulls air, making noise. Or, the siphon gets plugged, the water level in the weir rises, and eventually the emergency drain starts flowing, making noise and letting you know the main drain is not working correctly.

Once the drains are set, the only real change that should be seen is evaporation. That should show up in the return pump section and the ATO handles that.

Hope that explains things.

I can see now that this matches the description of the Herbie System. Red Sea adapted the idea to use a down pipe and an outer square pipe. In the Herbie System, a siphon is created that lets water flow down to the Sump. In the Red Sea version the siphon is created when water flows through the down pipe to the Sump but the siphon also breaks when the level drops below a point where air is introduced.

The DC Pump Rate is fixed so that I select one of the 20 speeds and keep it at this setting. Variations in my House Supply don't normally affect this, so for the setup the output rate is constant.

The bit I was missing, was about the siphon being a bit ahead or behind the pump. As the level in the weir height rises then the siphon is slightly stronger causing more water to flow down to the Sump and reducing (restoring) the level. When the weir height falls then the siphon is slightly weaker causing less water to flow down to the Sump and increasing (restoring) the level.

Or, as you explained, if the Pump rate is varied then an increase in the Pump speed causes the level to increase and the siphon to also increase which decreases (restoring) the level.

I'm aware that if things get out of hand then noises are created. Small adjustments of the Diaphram Valve are required and also patience to wait for the System to stabilise.

The new Red Sea Valve has a Red Cover and around the edges small marks about 0.5cm apart on the grey body. Adjustment is claimed to be 4x better than before and (for my flow rate) an adjustment turning it one to the next mark is sufficient. I just have to remember to turn it clockwise to reduce the flow and so increase the height in the weir box and the opposite to increase the flow and lower the height.

Another change is the switch to Red Pipes. The Emergency Overflow Drain is also Red and it is possible to see the height that the weir is below the top without removing the cover when looking through the slots.

Knowing that the siphon rates varies to alter the flow so as to maintain the balance between input and output flows is good to know as it explains why the system works as it does - thanks.

 

[RocketEngineer]

Just keep in mind there are limits to how well it self corrects and you’re good. That’s why you want to leave things for a while between adjustments once you have it close. Small changes can take a while to show up one way or the other so make haste slowly. Good luck.

 

[tbrown]

+1 to the above!

It sounds like you're doing good. One thing with weirs is just to remember that you don't want it to go into the emergency overflow if it can be avoided. That's there in case the weirs get plugged up or you have a sudden burst of water meter the tank (water changes with the tank running...). I set my flow I want in the tank and adjust the overflow slightly higher or lower depending on where I want the tank level. Some people set the overflow (or don't have an adjustable overflow box) and then adjust the flow from the pump to set the tank level.

 

[Simon_M]

Just keep in mind there are limits to how well it self corrects and you’re good. That’s why you want to leave things for a while between adjustments once you have it close. Small changes can take a while to show up one way or the other so make haste slowly. Good luck.

I do leave things for a while. Otherwise it becomes an oscillating System as you go from one side of "right" to the other. The new Diaphragm Valve which has markings around the outside of the body. This helps me because an adjustment moving from one to the next is about enough. To speed things up, I did find removing the centre weir "comb" to let water in/out and then replacing it and noticing if the water level goes up/down - can speed things up.

Best of all is to make an adjustment e.g. to the next "mark" and then forget about it for five minutes. It also helps to remember that closing the Valve restricts the output back to the Sump so increases the Weir Water height - I did this the "wrong way" a few times!

 

[Simon_M]

+1 to the above!

It sounds like you're doing good. One thing with weirs is just to remember that you don't want it to go into the emergency overflow if it can be avoided. That's there in case the weirs get plugged up or you have a sudden burst of water meter the tank (water changes with the tank running...). I set my flow I want in the tank and adjust the overflow slightly higher or lower depending on where I want the tank level. Some people set the overflow (or don't have an adjustable overflow box) and then adjust the flow from the pump to set the tank level.

Folks seem divided between those that like a trickle of water through the emergency overflow - so that they have a "positive" influence and use this to regulate the height, others don't.

I also like the idea that the emergency overflow shouldn't have water passing down it e.g. should be dry. Keeping it unused means that it won't get stuff growing in it e.g. if it is needed then it is fully available.

My mistake (so far) has probably been to (aim to) set the level too far below the emergency overflow. It is probably best to aim for only just below the top...

 

[tbrown]

Folks seem divided between those that like a trickle of water through the emergency overflow - so that they have a "positive" influence and use this to regulate the height, others don't.

I also like the idea that the emergency overflow shouldn't have water passing down it e.g. should be dry. Keeping it unused means that it won't get stuff growing in it e.g. if it is needed then it is fully available.

My mistake (so far) has probably been to (aim to) set the level too far below the emergency overflow. It is probably best to aim for only just below the top...

That's personal choice I'd say. I tend to keep my water level just above the bottom of the trim on my tank so I don't see the water line. It doesn't work as well on rimless tanks though so on my 5 gallon I tend for about 1/4" below the rim. Also, the higher you run the water level the more salt creep you end up with outside the tank.

 

[Simon_M]

The Weir on the Red Sea Tanks sets a low/high level that is about 4cm below the top - it's a rimless tank.

At least for now the "mystery" of how it works is "solved" and I've now found several videos about the Herbie Drain System. Thanks everyone.