Siphon Overflow Myths?

[ChrisRD]

What would be a safety for your pump not to burn out?

Jandree22 had mentioned a float valve to cut off pump.

Actually it's a float switch, not a valve (there is a difference- float valve is something else), and it was Righty who made the suggestion.

Not trying to give you a hard time, just wanted to clarify. :wink:

 

[Anonymous]

From the sound of it, you like your CPR. I'm glad it work's for you.

Yes but I can see where people have problems with them, I can also see where people would have problems with a Lifereef, from a design standpoint. Any J-tube could flood, as could any CPR, I like the addtional security of a pump http://www.premiumaquatics.com/Merchant ... 3-AQUALIFT
(not a powerhead-the distinction is very important) connected to clear the siphon tube. Both of the floods you described were due to a lack of maintanence IMO, and therefore preventable. I think there may be less maintanence involved with a lifereef, but aren't they quite a bit more expensive? Eventually I'm going to drill my tank anyway.

 

[xrunner123]

Any J-tube could flood, as could any CPR, I like the addtional security of .....

Totally false. You are mixing problems together. If you flood due to lack of overflow, it is because your SUMP is NOT designed properly.

And as far that deviceis concerned- It is just one more mechanical thing to worry about.

It all boils down to things that can go wrong and probablities. If I had a choice to either go with a CPR with a pump/powerhead or a U-tube design, I would go with the latter. If I had a choice of either the U-tube or drilled tank, I would go with the drilled tank.

Want to totally eliminate ALL possiblities of a flood or some accident, don't get a tank and move to the desert. :wink:

 

[sstephen]

As far as flooding goes, maybe you guys are talking about two different situations. It seems as though Xrunner is refering to a loss of siphon causing much of the water in the sump being pumped back into the tank causing a tank overflow. He's right in that a properly designed sump will not do this, although the pump may burn out unless there is a float switch being used to cut it off. On the other hand, kevlouie seems to be talking about the external section getting blocked and then overflowing. The actual siphon is between the internal and external overflow boxes. Please correct me if I'm wrong, but unless the external box water level rises higher than that of the internal one, the siphon can continue draw water into it causing a flood. I've been thinking about this topic for a while as I'm planning a sump and external overflow (no other way to do it at this point). Is it possible to eliminate the external overflow box and simply use the internal one? I would think that it could work as long as the water flow overflowing into the internal box was as fast, if not faster, than the water flowing through the siphon. I'm not fluid dynamics expert, so I was just going to experiment with it.

Scott

 

[esmithiii]

Sstephen-

The external box is essential. If you do not have it the water will rush too fast into the sump. If the water is sucked too fast, the internal box will empty, the syphon tube will suck air and the syphon will be broken. If your sump is more than a couple of feet below the level of the top of the tank, it will syphon so fast you would need a large return pump. The problem then is that you must ballance perfectly the rate of syphon with the return pump. If it is mismatched, the water level one side of the syphon will drop below the tube and it will suck air and the syphon will be broken. This is the primary reason that there is a divider in the outside overflow box.

 

[xrunner123]

Wow, getting to be a long thread.

On the other hand, kevlouie seems to be talking about the external section getting blocked and then overflowing. The actual siphon is between the internal and external overflow boxes. Please correct me if I'm wrong, but unless the external box water level rises higher than that of the internal one, the siphon can continue draw water into it causing a flood.

If the external section gets blocked, say if we just totally block the line going TO the sump, the external box level would rise and keep on rising, until the level is equal to the tank level. At this time, siphon would stop- water doesn't run uphill. There would still be water in the U-tube, but just not moving. When you unclog the block, siphon will be restored.

If you cut off power, siphon will continue to fill up the sump until water stops flowing into the internal box. My internal box is set about 1.5 inches down from the top so my tank will never drain below this.

esmithiii is right on the money regarding the outside box. It's basically there to regulate the water coming out so air doesn't get sucked in.

 

[esmithiii]

Forgot to mention- the box is also there so that if the power goes out then the syphon is not broken.

 

[sstephen]

esmithiii:
Don't you have to match the flow rates from the siphon and the return anyway?

Xrunner:
I understand that the siphon will stop once the water gets to the tank level. That's essentially what I meant to say earlier. But it seems that some people are somehow making the external box itself lower than the tank level. If you do that, then water will most likely overflow the external box itself as the siphon continues to draw water. I only mentioned this because a number of people seemed to have experienced this problem. But as you said, the simple solution is to make the external box capable of holding water up to the tank water line. Of course, the water line will get higher as excess water is pumped into the tank from the sump. So that has to be taken into account as well.

Scott

 

[esmithiii]

esmithiii:
Don't you have to match the flow rates from the siphon and the return anyway?

No. That is what the divider in the outer box is for.

 

[xrunner123]

But it seems that some people are somehow making the external box itself lower than the tank level....


Don't you have to match the flow rates from the siphon and the return anyway?

Oooo. That's a no no. Asking for disaster. Check out this picture http://www.lifereef.com/lg_pref.jpg. We also failed to mension that the external box has dividers in it, or is supposed to . That is the key to keeping the siphon there at all times. So it does not matter what the flow rate is, siphon is always there. 1 gph in = 1 gph down to sump or 1000gph in = 1000pgh down. Too too much flow will obviously not work.

Flow is controlled by pump and the system will always come to an equalibrium provided that you have enough water in the sump. At this point tuning is the same as if you had a drilled tank.

 

[LFS42]

Xrunner,
I do understand that you do not say
"overflows are better than a drilled tank"
But, I seem to be having a problem with you saying a properly
designed sump is needed to not flood a tank with a broken siphon.

Say my sump hold 5 gallons in the pump section
(meaning it will only pump 5 gallons in before it's empty)
I would need to have 5 gallons available in my main tank.
now, say I have a 55 gallon tank, 5 gallons is about 3-4 inches.
So now I need to keep my tank 3-4 inches lower than the top of the tank
I don't like the look of that, it make the tank look poorly maintaned.

Now l change my sump to only have 2 gallons in the pump area,
I can have 1 gallon/day evaporation, so I need to fill the tank every
other day at the least. What happens when I go away for a long weekend?

I understand what you are saying, but to say that flooding occurs in
poorly designed sumps rubs me the wrong way.
A properly designed sump makes maintenance easy and worry free
not daily.

Just my opinion,

 

[Anonymous]

I had to install a second U tube on my overflow to accomodate my surge devices. One of the two tubes would consistently accumulate air bubbles until it completely lost siphon. Never flooded my tank, because I had the additional U tube just barely getting all the water through. I think the problem was that while the surge devices were filling up, very little flow was going through the U tubes. Very little flow divided between two tubes= Bad.
Sorry, but the bit about a poorly designed sump just does not hold true in some cases. If I've pumped 5 gallons into surge devices, and THEN my overflow decides to lose siphon, my tank WILL overflow. It doesn't matter if my pump is sucking air/burning out/turned off, because the water is already up there, and my tank can't hold an additional 5 gallons without flooding.

 

[xrunner123]

Say my sump hold 5 gallons in the pump section
(meaning it will only pump 5 gallons in before it's empty)
I would need to have 5 gallons available in my main tank.
now, say I have a 55 gallon tank, 5 gallons is about 3-4 inches.
So now I need to keep my tank 3-4 inches lower than the top of the tank
I don't like the look of that, it make the tank look poorly maintaned.,

Make the water line just above the trim of the tank. On my 125 it is 2 inches down, so I have 12x72x2/231 = 7.48 gal. I run about .5 inches above the over flow at equalibrium, so that leaves me with 5.6 gallons of 'reserve'. This does not look poorly maintained. When I remove the u-tubes I just barely not overflow my tank.

Now l change my sump to only have 2 gallons in the pump area, I can have 1 gallon/day evaporation, so I need to fill the tank every other day at the least. What happens when I go away for a long weekend?

1 gallon a day is alot and evaporation will be a problem. I have glass covers and I get about 1-1.5 gallons per week, so a weekend is not a problem for me. Now if you run without a glass top that may be a problem.

I understand what you are saying, but to say that flooding occurs in poorly designed sumps rubs me the wrong way.
A properly designed sump makes maintenance easy and worry free
not daily.

Well if your tank is 55 gal and your sump is 125 gal with no dividers, you could go a long time without compensating for evap water, but if your overflow fails you will pump 125gallons onto the floor. If you have the tank baffled properly you can pump 5 gallons back in case of an overflow failure. So yes a poorly designed sump can screw you.

BUT the whole system have to be designed smartly. I would say that if you have a drilled tank, the likelyhood of an overflow failure if so much less than that of a U-tube design, you could have a sump that has, say, 20 gallons of backup for evap. On a tank with a U-tube or CPR, I would NOT have a sump capable of overflowing the tank. Too risky.

Oh if your sump can overflow your tank, one way to ensure that it doesn't is to put one or two (for redundancy) float switches inside the tank.

 

[xrunner123]

I had to install a second U tube on my overflow to accomodate my surge devices. One of the two tubes would consistently accumulate air bubbles until it completely lost siphon. Never flooded my tank, because I had the additional U tube just barely getting all the water through. I think the problem was that while the surge devices were filling up, very little flow was going through the U tubes. Very little flow divided between two tubes= Bad.
Sorry, but the bit about a poorly designed sump just does not hold true in some cases. If I've pumped 5 gallons into surge devices, and THEN my overflow decides to lose siphon, my tank WILL overflow. It doesn't matter if my pump is sucking air/burning out/turned off, because the water is already up there, and my tank can't hold an additional 5 gallons without flooding.

Try lowering your internal overflow box to just above the trim, this will give you more reserve. And what is surge devices?

One would think that installing an extra U-tube would help out the overflow, but it doesn't. You answered yourself. By installing the second one you starve the first one- the water velocity drops, thus the ability to clear air fails. The key is the velocity of water when in operation, not when just starting.

Did you make your own overflow? Do you have a standpipe? You have to be careful because a badly designed overflow will not clear air. A standpipe that is as tall as the top will do this. There is not a big drop for the water to generate a strong suction/siphon. The best overflow box is one with a very big drop to the external box. This will yield the strongest currents in the tube.

When I first got my overflow I had some fun and did some experiments. I can blow a half dollar size of air in both tubes, turn on my pumps and they will clear in a minute- before the sump runs out of water.

 

[esmithiii]

After reading all this I am doubly happy that I have a drilled tank.

Ernie

 

[LFS42]

After reading all this I am doubly happy that I have a drilled tank.

Ernie

me too

 

[Anonymous]

A surge device is a bucket that dumps all its contents at once into the tank, refills, then dumps again. It creates an enormous amount of flow compared to powerheads or pumps. When I dump 5 gallons of water into a 30 gallon tank in about 30 seconds, there's no way one U tube can handle it. The second U tube is necessary. I don't know the brand of my overflow, but it's definitely not a CPR.

A standpipe that is as tall as the top will do this. There is not a big drop for the water to generate a strong suction/siphon. The best overflow box is one with a very big drop to the external box.

Look at the water level in your internal box, and then your external box. It's the same height. Whether your standpipe is 1" or 12" below the tank water level makes no difference in the capability of the overflow. The size of the U tube is what limits the flow.

 

[xrunner123]

A surge device is a bucket that dumps all its contents at once into the tank, refills, then dumps again. It creates an enormous amount of flow compared to powerheads or pumps. When I dump 5 gallons of water into a 30 gallon tank in about 30 seconds, there's no way one U tube can handle it. The second U tube is necessary. I don't know the brand of my overflow, but it's definitely not a CPR.

2 overflows would be better with 2 feeds to the sump. A second U-tube reduces internal water velocity to low levels. Is this a DIY job?

Look at the water level in your internal box, and then your external box. It's the same height. Whether your standpipe is 1" or 12" below the tank water level makes no difference in the capability of the overflow. The size of the U tube is what limits the flow.

If internal box and external box height is the same then how do you get siphon? Can't happen. That is the physics behind siphoning. What you siphon INTO has to be lower than the source. The lower it is the more pressure is generated and the higher the flow rate.

Look closer at your overflow- better yet take a ruler and measure the differential distance between the internal and external box. Mine is about 1/2.

The standpipes in a drilled tank is different. That height does not matter (1 inch or 12 inches), but in a siphon with internal/external boxs it does to some extent. I'm tired so I won't get to deep into it. But yes, a stand pipe as tall the top will not work right. There won't be enough drop. Just make the stand pipe 1/2 the distance of the box.

And the reason that I said "The best overflow box is one with a very big drop to the external box." is let's say you put some air into the tube, then the flowrate drops, the external box level drops, the pump pumps more water into the tank at a higher rate than the overflow can get rid of- to try to come to an equalibrium, the internal box level rises (as so the external level lowers). More water is sucked out at a faster rate (since the delta in height is more) until the air bubbles leave. The tank will then come back to an equalibrium state.

Soooo, if the drop is say to the floor that is 3 feet away, you have 3 feet of water weight to pull the air out- the velocity of water will be VERY VERY high until the external box level rises and equilibrium is reached again. At equilibrium you may have a very very close water height but not the same.

This is an extreme example, but you get the point. So if the overflow is small, it is possible that air bubbles can accumulate and stop siphon. This often occurs with DIY systems. Call the guy (forget his name) at Lifereef.com. He is very knowledgeable and will explain the whole theory and the pros/cons of different makers.

Make sense?

 

[buff1]

I'm late joining this post, but I'm firmly in the camp that siphons are just disasters waiting to happen. Some people have had snails crawl in and disrupt flow, but I've had several overflows occur simply because the siphon was interrupted. The primary cause was that tiny bubbles in the main tank make their way into the u-tube and consoladate there. Eventually the air in the tube becomes great enough that flow becomes reduced. Then the sump either gets lower and lower until air starts being sucked into the return pump or the automatic fresh water float gets triggered and flows until it is emptied, at which time the water may be overflowing in the main tank. I have also had the siphon break when power was lost to the tank so when power was restored the return pump just kept running until the tank overflowed. No matter how it happens you have to assume that the worst could occur and the best way to prevent siphons from breaking is to not have them and rely on gravity.

 

[xrunner123]

I'm late joining this post, but I'm firmly in the camp that siphons are just disasters waiting to happen. Some people have had snails crawl in and disrupt flow, but I've had several overflows occur simply because the siphon was interrupted. The primary cause was that tiny bubbles in the main tank make their way into the u-tube and consoladate there. Eventually the air in the tube becomes great enough that flow becomes reduced. Then the sump either gets lower and lower until air starts being sucked into the return pump or the automatic fresh water float gets triggered and flows until it is emptied, at which time the water may be overflowing in the main tank. I have also had the siphon break when power was lost to the tank so when power was restored the return pump just kept running until the tank overflowed. No matter how it happens you have to assume that the worst could occur and the best way to prevent siphons from breaking is to not have them and rely on gravity.

Read some of my replies. In a properly designed U-tube overflow, air does not consolidate. The water flow is too high (provided you run at near or at the rated gph). And if it does, it will get swept away.