Understanding a floating weir?

[LuapYllier]

OK so I am looking around for a skimmer that will work in my situation (which by the way is a lot harder than I thought it would be...I figured there would be stuff designed for block wall applications based on how many KOI ponds are built that way and most of you guys are building natural rock and dirt ponds so I didn't get much help in my thread asking for suggestions) and I am finding myself confused by the "floating weir". I work in civil engineering field as a drafter so in my mind a weir is a concrete edge that allows water to flow over at a certain elevation to maintain a water level in a storm water pond.

I went into this thinking that the bottom of the opening leading into the throat would be said weir elevation. Now I am seeing this floating weir flap thing and am totally confused. What keeps the flap from just folding in flat? How do you determine where your water level is if this flap keeps moving around? Is the floating weir even a good idea or should I look for something without one?

 

[jgrandmont]

Here's a picture of a floating weir in a pool application which is based on the same principle. The float (or flap) sits at the weir opening and is hinged at the bottom, allowing it the move freely up and down with the water level. The only time it would lie flat is if the water level drops to the very bottom edge of the weir opening (or below). It's a good idea to use one if you plan on having fish in your pond.

 

[combatwombat]

In a pond application, the weir door is hinged at the bottom and is not intended to set water level but to swing up and down to maintain surface tension with a dynamic water level.

 

[poconojoe]

I'm guessing the door is lined with styrofoam to keep it buoyant, like the door on my pool skimmer.
The pump creates suction, the door is pulled in and opens.
When the pump shuts off, the door floats up to the closed position.

 

[LuapYllier]

In a pond application, the weir door is hinged at the bottom and is not intended to set water level but to swing up and down to maintain surface tension with a dynamic water level.

OK so if the weir is not determining the water level (like every weir I have experience with) then what is?
I have a waterfall in my front pond and the elevation of the "chute" the water comes out of is the weir and determines the level of water in the basin.

 

[poconojoe]

I think we are talking about two different things here.
1. A stationary weir.
2. A floating skimmer, not a floating weir.

By your definition, a weir would permanently determine the water level.

A floating skimmer has nothing to do with the water level, it's just a skimmer.

At least that's the way I see it, I could be wrong.

 

[LuapYllier]

I think we are talking about two different things here.
1. A stationary weir.
2. A floating skimmer, not a floating weir.

By your definition, a weir would permanently determine the water level.

A floating skimmer has nothing to do with the water level, it's just a skimmer.

At least that's the way I see it, I could be wrong.

Yes we are talking about different things. I only know about the stationary weir type. The diagrams call this flapper door a "floating weir" which as you say isn't really a weir since it goes up and down with the water level. I am trying to understand how this all works. I guess the water level would be purely determined by the balance of how much water is being pumped in vs how much water can escape through the skimmers drain.

I am also seeing something called an equalizer pipe at the bottom of some styles of skimmer. I am not sure what that is for.

Another question I now have is if I am not using a pump to suck water through the floating weir will it still function on just a gravity outfall? I was going to have this drain directly into another area with no pipe and no pump.

 

[LuapYllier]

So if I am understanding this correctly, lets say the skimmer I get allows 1000gph to exit the pond. I need a pump that will pump that same 1000gph back into the pond plus any loss from passing through plant bog or evaporation or whatever...lets call it 1005gph pumping in. This will keep the pond level at a constant elevation but nothing in this system determines what exact elevation that will be. If i add more water to the pond it will maintain that new elevation. If i remove some it will maintain that. If there is too much water in the overall system it will overflow, if it is too little it will stop going out of the skimmer and eventually the sump pump will cut off (switch suggested by members).

So I will need to manage the water volume separately from this system. An overflow port to a drain line for if we get heavy rains and a float switch to a solenoid controlled water valve for refilling should do that right? The differential distance between valve on and valve off would be what controls the water level?

 

[Mmathis]

Oh wow, this is way beyond my simple comprehension of how a pond works

 

[poconojoe]

So if I am understanding this correctly, lets say the skimmer I get allows 1000gph to exit the pond. I need a pump that will pump that same 1000gph back into the pond plus any loss from passing through plant bog or evaporation or whatever...lets call it 1005gph pumping in. This will keep the pond level at a constant elevation but nothing in this system determines what exact elevation that will be. If i add more water to the pond it will maintain that new elevation. If i remove some it will maintain that. If there is too much water in the overall system it will overflow, if it is too little it will stop going out of the skimmer and eventually the sump pump will cut off (switch suggested by members).

So I will need to manage the water volume separately from this system. An overflow port to a drain line for if we get heavy rains and a float switch to a solenoid controlled water valve for refilling should do that right? The differential distance between valve on and valve off would be what controls the water level?

Let me know if I'm understanding you correctly...

I think you are basically describing a spillway which will maintain the water level and dumps the water into a holding pool.
Then your going to pump the water from that holding pool back into the pond.

Your idea is a bit different than most designs, I think.
The good thing is the pond level should be constant all the time, even if the power goes out. I'm assuming that is what you are trying to achieve.

 

[combatwombat]

Let me know if I'm understanding you correctly...

I think you are basically describing a spillway which will maintain the water level and dumps the water into a holding pool.
Then your going to pump the water from that holding pool back into the pond.

Your idea is a bit different than most designs, I think.
The good thing is the pond level should be constant all the time, even if the power goes out. I'm assuming that is what you are trying to achieve.

if that’s what it is, that’s a common negative edge skimmer detail. @Lisak1, @GBBUDD, and others I’m sure, have that type of skimmer. And I am building one now.

 

[GBBUDD]

The water level at least in my case when the power is running yes constant water level it never fluctuates which is very nice. How ever when the power goes out i you don't have a VERY WIDE im talking like 8 foot wide over flow for the negative edge. when the power goes out your water level is going to drop one for the loss of constant flow two the absolute hardest part to the negative eg is making the pond water proof right up to the edge of the over flow in my case a flat boulder i had to make the boulder have the rubber from the pond loop all the way up to the top of the bolder fold under the boulder and make that water tight to the boulder the fold then drops into a catch pond. now i made my catch pond a little to small you have to think about if the power goes out when the pump kicks back on will you have enough water for the pipe to push enough water to refill the pond to where it begins to fall back into the catch pool . It works but it throws a ton of air until the cistern pump can refill the catch pond to where it balances out again. @combatwombat please not the above

 

[combatwombat]

@GBBUDD: Isn’t your cistern 3000 gal? And it’s still too small?

 

[GBBUDD]

Yes it is . The order is like this .
Negative edge drops to sh_ts creek . If a fish goes over the negative edge it falls into a small pool about 6' x 6' this is where i moved the intake to the main pump 12000 gph and disconnected the old skimmer. So the main drain and now Shts creek are my inlets to the pump. That small pool then has an over flow where it drops into the 3000 gallon cistern. "Hells gate". Any fish that drops into this area gets caught in a non woven fabric bag that i made and they are probably not coming back. So there is a small pump from the cistern that circulates the cistern pushing the water up to the pond. The 6x6 should have been almost double the depth being only a foot deep so when the power had gone out there was a nice cash of water for the pump to push reestablishing the height of the pond.
I could not place the intake of the main pump in the cistern like i wanted to as the external pump can not pull /lift the water up from 6 feet below the height of the pump.

 

[combatwombat]

@GBBUDD: Got it. Sounds like the cistern size is fine, but you're pulling water from in front of the cistern, and that area isn't quite big enough. I was going to ask about your skimmer and if you disconnected it or not. Sounds like it's been removed.