Pond Boss Forums POND CONSTRUCTION Renovating a Pond or Lake? Question about pond siphon air vent location

Currently my vent is about 4 inches above normal pool. I want the siphon to start faster but I am worried that if I place the air vent below normal pool the air trapped in the system wont start the siphon after the water line goes above the 10" pipe. Another question I have is most engineering sites want the pipe below pool with holes drilled into the pipe until just about normal pool? What are the holes intended to do? Break siphon slowly?

Last question... If the 4" vent is submerged before the water line is over the top of the 10" pipe will it siphon at all? Or will it still function as a normal drain until its completely filled.

Thanks guys.

Anyone??

I don't have any experience with a siphon system, but, I think I understand the concept. The siphon action won't start until all of the air has been displaced in the pipe by the rising of the pond's water level. Or, you can manually fill the pipe with water, while bleeding the air at it's high point. Then, open block valves at each end, to begin the siphon. The purpose of the vent is to automatically break the siphon when the surface water has receded to a desired level. At this level the open end of the vent pipe is exposed, which allows air to enter the system. If not for the vent, the pond would drain until the water level dropped far enough to expose the intake end of your overflow pipe. If you lower your vent, you will only delay the breaking of the siphon. It won't hasten the beginning of the siphon.

As to the question of why the engineers suggest placing the end of the vent pipe below the water's surface, and drilling holes in it; I'm guessing, maybe it's a way to prevent a piece of floating debris from be sucked up into it, and clogging it.

Just a thought, but, if you did install a second siphon, like you mentioned in your other thread, maybe you could place the opening of the intake at desired water level, and draw water off the top, thereby eliminating the need for a vent. The siphon will be broken when the water level drops, exposing the top of the pipe. Of course, you would need a trash guard.

I'm sure you already knew much of this. Just my way of trying to explain. I find it challenging to discuss topics like this in a few words.

Yep, holes are for a trash gaurd. And as already mentioned, height of the vent won't affect when the siphon starts, as long as it's not higher than your 10" pipe.

When the siphon does start, what air is trapped inside the vent pipe will get sucked through and then for as long as the main pipe is in siphon mode, water will also flow through the vent pipe. "Flow" is too gentle a word, though, it's actually pretty violent. Thats why it's a good idea to anchor your vent pipe.

Now this confuses me. I am like Gully washer, in that I have no experience with a siphon, but I have read a lot about them because I want to install one someday.

The height of the vent determines when the siphon is turned on and when its turned off. If it was below the outflow pipe, then the outflow pipe determines when it turns on, but the vent would determine when it is turned off. Also if the vent is below the outflow pipe, I would think that there may be more of a chance to have trapped air. .... Am I wrong about this?

My thought in the holes would be a trash guard of sorts. Not for water being blocked from getting in, but for an insurance that the siphon mode will break seal and not drain the whole pond out.

Mike-- does your inlet of the siphon go down deep into you pond? Or is the inlet just at water normal water level?

http://www.ponddampiping.com/syphon1.html

When the vent tube is uncapped or above the water, you will never attain a "siphon" as air is being pulled into the pipe from the vent and it only drains. A "siphon" starts when the vent tube goes under water AND the top pipe is below the pond water height, then, flow velocity is increased drastically due to the head water weight shifting to the drain pipe inlet rather than head water weight being only above the top of the crossover drain pipe.

The "holes" drilled into the vent are to both prevent clogging and to help lessen whirlpooling at the vent pipe....trash guards are always a good idea on both vent and inlet pipes.

A clog on a vent could cause you pond to drain completely and a clog at the inlet could prevent flow and cause a dam breach (or a deadly situation trying to unclog)

Rex is right on point. I had a single vent and a turtle got caught in it during a big rain. Puddle had dropped a foot below vent before I caught it.

I fixed that problem quick.

Last time mine siphoned, there was alot of grass and small woody debris that collected at the vent. Pretty concerning, but it didn't clog. I never thought of having 2 vents, that's a good idea.

I suspect mine may have siphoned again last night, but I didn't have time before work to go inspect. Got just shy of 4" overnight. From the house I couldn't see any evidence that water had gone over the emergency spillway, I'll have to check it out this evening.

Rainman, that's all been my thinking on the process as I have read it.

The way you wrote the shift of inline pressure is excellent. That's the first time I have really grasped the idea of how the pressure is increased. Thank you.

Please tell me I didn't screw up the installation of this system. In order for me to get the water level I wanted, I had to place the main 10" pipe about 17" down in the dam. So in order for my Air vent to be completely submerged the water would be over the dam! I thought that it only mattered that the opening of the vent be submerged and the siphon would start no?? Does the water pool level need to be over the horizontal piece of the air vent? Pond in siphon

Does this look like it is siphoning?

My inlet or the 10" pipe goes down into the pond about 20 feet. The air vent horizontal piece is actually above my dam height. ( I know I need more dirt to make the dam higher.) The vertical piece drops down and is currently about 8 inches above normal pool.

Mike, if I understand it correctly, it doesn't go into siphon mode until ALL pipes, inlets, vents, etc are under water. Can you take a pic of your upper setup. Its hard some times to grasp everyones different lingo for items and such.

If you take a look at that link I posted, it shows the vent just under the height of the spillway. This could be your problem, easily fixed if it is.

The horizontal part of your vent pipe at the top or above the top of the dam is the typical design (see fish's link) and will not cause the dam to be topped. The important part of the vent is the inlet.

I think the amount of air still in the vent pipe when the inlet is submerged is neglegable and does not prevent the siphon from starting.

Vamaz, could I add to your quote and say it this way

"The important part of the vent is the height of it's own inlet."

...and it should not be higher than the emergency spillway.

Yes, but Ideally you would want some freeboard between the level of your vent and the spillway so they wouldn't both come into use at the same time. The emergency spillway should be a backup incase the siphon couldn't handle the rising water.

I've got about 8-12 inches from the top of the 10" pipe then my spillway kicks in.

Looks like a correct installation to me. Like the others said, it's the elevation of the vent opening that is critical. The lower it is, the lower the pond's water level will be when the siphon action stops. Regardless of the elevation of the vent opening, the siphon action will only start when the pond's water level reaches the same elevation as the high point of your siphon pipe, and the end of the vent pipe is submerged. Also, make sure that the threaded plug in the vent cleanout is not leaking. A leak anywhere in the vent would suck in air and break the siphon effect.

Well be just got an inch of rain and the pond siphon is working but I also have water going down the emergency spillway. I'm thinking by the time the water is over the 10" pipe to start siphoning I am already at emergency spillway elevation or close to it. I just dont have the added capacity to allow time for the siphon to keep up. I think the answer is to add 2 or three feet to the dam brest.

The amount of freeboard necessary between the primary and emergency spillway depends on many variables and will vary from pond to pond, but unless you just experienced an unusual rainfall event, it does sound like you need more.

Be careful adding height to the spillway because no matter how you compact it, fill material will always erode easier than natural undisturbed soil. On page 31 of USDA Agricultural Handbook 590, it talks about this saying that an auxilliary spillway should be excavated into the earth for it's full depth, otherwise vegetation or riprap should be added for protection.

http://www.in.nrcs.usda.gov/pdf%20files/PONDS.PDF

Mike, your dam crossover pipe functions the same as if it were a straight drain pipe through your dam.

If you wanted your normal pool level at X freeboard, that should be where the inner bottom of your crossover pipe should be. As water rises above normal, your pipe drains normally. If you set the inlet height of your VENT pipe at say, 5 inches above normal level, you would still not get a siphon started until the pool was above the TOP of your crossover pipe and has evacuated enough air in the system to start a siphon (because your vent inlet is under water and "sealed") The siphon would theoretically break when the pool was back to 5" above normal pool and the pipe becomes a normal drain again..in reality, due to whirlpooling, a 5" rise set on the vent will break at 7-9" above normal pool

I just went down to the dam again and the water is rising slowly. For some reason the 10" pipe just cant keep up with the water. I sized the pipe based on recommendations from one of the internet companys I wont mention. They asked what my watershed was I told them about 70 acres and it's stream fed. The size of pipe recomended was 8". I bought 10" for that added comfort. Now I see that regardless, the 10" cant keep up with the rainfall we've been having. It's probably going to cost anoughter $1500.00 to add a second 10" siphon bringing the total of this adventure to $6500.00 That just sounds crazy to me. If I add another 2ft of fill to the dam I'll prob be around 9000.00

I've got plenty of rip rap thats for sure! lol the whole back side of the dam was loaded with it. I'll probably only raise it 8 inches. If I add 2ft to the dam height and add a second 10" siphon it better take care of it.

Sounds like it. Are you absolutely sure that the vent is at least as low as the top of the crossover pipe? If so, the crossover pipe was set at to high of grade. That hurts