I have a pipe inside my pond with an inlet at the bottom (AKA - the pipe is open on the end). The pipe goes up the inside and thru my dam at the fill line, then across the dam and down at a slight angle, to the backside of the dam where it angles sharply down to the bottom of the backside of the dam and exits there. The exit is lower than the entry point inside the dam.
In this scenario - wouldn’t gravity (vs. siphon) cause the pipe to drain once the water level in the lake hits the bottom of the highest point of the pipe?
Additionally, I have a siphon hole at the top of the pipe where it angles back inside the dam. As far as I can tell, there will never be an actual "siphon" unless I plug the hole and create one myself.
My point is that you could install a simple bottom draw drainpipe in this configuration and forget about all of this siphon stuff (as long as you have some type of vaccum breaker)…right?
Wrong. A siphon is only a siphon when the air vent gets closed off by the high water level in the pond. Until this happens, as you say, the water will just trickle through the pipe when the level is at normal pool. But when the water gets high enough to close the air vent, watch out because a siphon can flow almost 5 times as much water through the pipe as gravity can. Once the siphon lowers the water and uncovers the vent, it goes back to a gravity feed again.
I see what you are saying, its a garvity drain until the water level rises above the shut off (valve or breaker), then it becomes a siphon until the level goes back down. Got it, Thanks.
Jersey, I gotta ask. How is it that you figure a siphon can move water faster than gravity. A siphon is totally run by gravity and its potential can only be the difference in the height of the water from the surface in the pond to the outlet of the syphon. Maybe I don't understand what your system looks like and the placement of this air vent. It is true that an air vent at the highest point of the syphon tube will make a pipe no different from a spillway until the water covers the vent. Is that what you mean? If so, then it is true that the syphon can result in much higher flow because the height difference between inlet and outlet for a spillway may be only a fraction of an inch while the end of your syphon tube could be many feet below the water height in the pond. I'm new to pond management and my pond does not have a dam or overflow need. It would seem that what you describe would be a good way to accomplish overflow that is just a trickle when pond level is relatively close to what you want and then automatically goes into syphon mode so that flow goes up sharply if the level suddenly gets too high. Ingenious, but why do you do this unless you need to have the pipe inlet on the pond side always below the water surface but don't want to drain down below the highest point of the pipe. Is this a common need for ponds?
bz,
You are correct that a siphon is totally run by gravity. When I said that a siphon would flow more water through a given pipe size than gravity could, I was comparing a siphon to a standpipe system. You are again correct that this is because of the added head pressure that a siphon system has, and a standpipe does not.
Why do I think this is better? Well, my yet to be built pond will be on a small spring fed creek. Most of the time my two 12" siphons will be acting like a spillway with the water just trickling through. But when the terd-floater storms come through and the water rises, it will go into siphon mode and hopefully be able to handle all of my 320 acre watershed before it gets up to the emergency spillway, also known as my driveway. I don't like the look and constant noise of a standpipe and all of the trash that collect around it.
More good reasons for a siphon...It draws water from the bottom of the pond, pulling the oxygen-rich water down from the surface. It doesn't require a pipe through the base of the dam where a leak is expensive at best and dangerous at worst. If I ever need to drain the pond, all I have to do is cap off the air vent and wait about a week.
The flow potential of a syphon is determined by diff. in ht. of pond side pipe inlet and how low the pipe outlet is below this behind the dam. it can be several times the flow rate than gravity drain alone. It can suck out the 'bad' water and muck if placed near bottom.
Originally posted by burgermeister:
The flow potential of a syphon is determined by diff. in ht. of pond side pipe inlet and how low the pipe outlet is below this behind the dam. it can be several times the flow rate than gravity drain alone. It can suck out the 'bad' water and muck if placed near bottom.
It's amazing how much water a 4" pipe can siphon with only a 2 or 3 foot head. I think it could drain off a 10" rain from my 1.5a pond in 2 days or less. Right now I have to hand start the siphon with a hand bilge pump, but will add a vent with a flapper when and if I ever complete my pond.
Jersey, I think this is a brilliant idea, simple, elegant, and run by water level and gravity. I'm very familiar with syphons but never thought about how a vent in the top could be used to cause it to go into syphon mode when desired. Without the vent it will always be in syphon mode until the water gets too low then you'd have to start it by hand. Burgermeister, I think what you mean is the syphon head is the height difference in the pond level and the syphon outlet, not the difference between inlet level and outlet. The inlet could be at same level as outlet or lower and it will still work. Sometimes it hurts to think about how something even so simple works if I think too much.
It would still work, but the greater the inlet and outlet height difference,, the more suction. There is a formula, but dont have time now. Will post it later.
It has to do with acceleration.
bz is right again. The pressure is determined by the difference between the pond water level and the siphon outlet. It would work just the same if the inlet was just below the surface. But you put it at the bottom for obvious reasons.
Look here -->
SIPHON SYSTEM
Jersey, in your example you are correct because that outlet end is not much lower that inlet level. This is due to the pressure of the volume of water is helping with the outflow. BUT, I will guarantee you that if you lower the outlet hole significantly, the flow will increase dramatically because thare will be much more water inside the inclosed system.
I my work, I have syphoned many ship gyro containers filled with liqued to do an annual overhaul and the higher I can get the container above the end of the syphon tube the quicker it empties.
I think we all are correct. the pressure of the water in the pond is relevent, also the height difference of inlet and outlet.
OK, you're right. My 2 reference heights were incorrect. they should have been the height of pond level and height of drain outlet.
Suffice it to say, since we can't manually manipulate the height of the pond, if we get the outlet lower, we can get the pond drained faster to avoid disaster during a flood.
Yep, I will put some effort into getting the outlet of my siphon as low as possible since I will only have 14' of water at the dam.
I think I am going to add another 12' section to my drain outlet, then turn it up and see how far I can "shoot the water" when the siphon kicks in.
Actually I've seen recommendations of turning the outlet 90 deg. vertical to help prevent air from gurgling back up the pipe & stoping the siphon.
My only complaint of a siphon is when used to drain a pond for some reason (which happened to me at least twice) the siphon stops it is very difficult to get started again with the water level down in the pond.
I have one of the syphon systems like shown at
http://ponddampiping.com/syphon1.html On three occasions, the air vent got clogged with trash and with a heavy rainfall my pond has had an accidental drawdown.
I put a screen around the thing to trap trash.
Frank
re: extending drain pipe, just remember that 33 ft is the maximum from crest of system to drain point for water, or else you will lose the siphon.
This is because the weight of water in pipe will exceed the atmospheric pressure on the pond.
33 ft is the maximum from crest of system to drain point for water, or else you will lose the siphon.
If I understand siphons correctly, the 30 to 33 ft limit (literally, one atmosphere of pressure in feet of water) is how high you can lift water on the upward portion of the siphon (entry point to crest). Is there really a maximum limit on how far the water can drop going from the crest down to the exit (minimum limit would be that the drop has to exceed the climb)?
Theo, you have uncovered more of my fuzzy math. The crest to inlet ht. must be less then 1 atmosphere. Maybe I should stick to 1s and 0s also. Or at least to electronics. Anyone have an RF question about their pond?
Hey, at least I am perpetuating an interesting discussion. This ws a tough weekend, mentally and physically.
Ditto tough weekend here. The well/pump that feeds our house is acting up - pump won't deliver over about 55 psi without (somehow - pressure safety switch using wrong value?) shutting itself off (fortunately horse barn and water are a separate well; cattle drinking pond water from hydrant below the dam). Then it turns back on when it feels like it. We put in a new P-switch and have (probably) ruled out electric supply problems; I currently have things running in a reduced pressure range (42-50 psi vs usual 40-60 psi) until we can assemble all possible spare items we could use and then pull/replace the pump. All in about 400% humidity
Theo and Burgermeister,
- So the longer the outlet = the greater the siphon. right?
The bigger the drop from crest to outlet, the more force/pressure/siphon it will discharge with.
Of course, I have no experience with pond siphons, just a little with gasoline and a lot with diesel fuel (Ptuuey!).
No, the bigger the drop from pond water level to outlet, the stronger the siphon. The crest height does not matter as long as it is no more than 33' above the water level.
I would guess that at some point with a very long drop pipe , the resistance of the pipe itself would come into play. But I can't see this situation in a pond siphon system. Just like I can't envision a dam that is more than 33' above the pond.
Does anyone have any pictures of their siphon during construction?
Pardon my imprecise use of nomenclature. I was implying that it's impossible to make a bigger drop from the water level to the outlet without lowering the outlet wrt the crest. But it is of course the net difference between the inlet and outlet elevations that drives the siphon strength.
I don't think anyone but Governments can afford enough dirt moving to make the top of the dam 33' above the desired water level.
Theo,
Not meaning to beat a dead horse, but the inlet height and the crest height mean nothing to a siphon. It's the pond water level and the outlet that matter. I think you meant that.
Here is a (very) simple drawing of how my drain pipe is designed. The inlet is on the left side.
http://i4.photobucket.com/albums/y117/darnold01/drainpipe.jpg
Alligator,
How does your vent pipe ever get closed? It looks to me like the water would have to flow over your dam in order to close the vent. Shouldn't you shape the vent like an upside down U with the open end in the water at the desired level?
Jersey,
My vent pipe will close when the water level rises above the top of the 12" pipe. It is the same principle as the "upside down U" - except simpler. In this design there is a lot less pipe sticking up out of the ground (and a lot less pipe to break with your mower, tractor...etc.)
Gator
Alligator
I'm with Jersey from your drawing the water would flow over the dam before it would start siphoning.
The 4" pipe has to become clogged either with water or debris before a siphon would occur.
In the case of debris it would drain the pond.
That's how the drawing looks anyway.
All,
First, let me apologize to my high-school drafting teacher...Mr. Lambert, you taught me better than that. But hey, that was 25 years ago!
I re-drew the drainpipe to be more precise:
http://i4.photobucket.com/albums/y117/darnold01/drainpiperevised.jpg The key here is that the 4" pipe has holes in it - like a sewer field line pipe. Therefore, as soon as the water hits the mark where the 4" pipe joint goes into at 12" pipe (or more accurately, the first hole in the 4” up from the joint) the siphon will be made. Since the 4" is full of holes – the water does not have to flow over the top to make the siphon.
The design of having holes in the 4" pipe keeps debris out of the system much like an inlet cover. This is much simpler than the “upside down u” design but works on the same principle.
Gator,
I understand your description and drawing but I think you will find a problem with the way it is setup. I may be wrong, but any hole allowing water to enter the 4" pipe will not be enough to completely seal off the 4" pipe starting the siphon. The 4" pipe would have to be completely covered or underwater for the siphon to start.
The slightest amount of air entering the 4" pipe will break the siphon or prevent it from starting.
Was there a reason you went to 4" pipe? A 1/2" "U" will do the necessary job of starting the siphon once the water level rises to block off any air entering it.
I hope your pond fills up soon and please let us know how the 4" works.
Dan
Gator,
I should have said that once the siphon starts it will suck the water out of the 4" pipe faster than the hole(s) can can allow it to enter, thus allowing air to break the seal stopping the siphon.
You could quickly make a miniture "model" out of 1/2" or 3/4" PVC with the same basic design and put it in a tub or bowl of water and see if there is a problem.
Good luck.
Dan
Dan,
I had the same thoughts as you, however, my pond guy - "has done 30 or 40 fo these" claims it works. I looked at a couple of his ponds and he seems to check out, overall. Havent seen one in sipohn mode yet.
I agree the question of the design is: Will there be a siphon when the water hits the 4" pipe OR will it suck air and just drain...(not sure I will be able to visually see much difference?) hopefully I will find out soon. Not much rain in the forecast right now.
On the question of the size of the 4". I agree with you, a smaller pipe would work. I never really asked "why" a 4". I suppose that was based on avaialblity of the pipe joint and/or habits of my contractor. One thing I have noticed about contractors is that they seem to find what works for them and stick with it.
I suppose if the siphon doesnt engage as planned - I can cut the 4" pipe down or replace it...there is no real reason to have a pipe there other than to eliminate the hole from becoming clogged.
Gator,
That makes sense. After 30 or 40 I'm sure he knows what works and what does not. While you are waiting for your pond to fill it might be interesting to make a small model and test it in a tub of water to see if it is obvious why it works.
Keep us posted.
Dan
Dan,
Let me further qualify this siphon issue on my design.
The design in my system is referred to as a "Vaccum Breaker", therefore implying that it is designed to eliminate a siphon vs. create one. This is an interesting idea to ponder...AKA, the design on my system is to drain until the water level reaches the fill line, then ensure the vaccum is broken. It is not designed to automatically create a vaccum? Perhaps so. In the standard "upside down u", the design is to automatically create and disengage a siphon. Two different designs.
Alligator,
Yep, that's a vacuum breaker. It is designed to keep a siphon from ever happening. Looking at your new and improved drawing, it appears that you might get a siphon going just as the water starts flowing over the top of your dam, but with the amount of vacuum a 12" siphon can pull, you would probably get a nice whirlpool over the 4" pipe that would easily suck in enough air to break the siphon. Even if the 4" pipe is a foot under water, a whirlpool can suck in a lot of air. When this happens, the siphon will start, then it will suck in air and stop, then it will start again, then stop, and so on.
I design large aquarium systems that use the same siphon system we have been discussing here. Most use a 1 1/2 inch siphon tube with a 1/2" vent. With this I can get a whirlpool to suck air down 3-4 inches below the surface. You can only imagine what a 12" siphon with a 4" vent can do. A 12" pipe is 64 times as big as a 1 1/2 inch pipe.
Your system would be very easy to convert to a real siphon system. If you want to wait and see what it does, I just hope you have a well built emergency spillway. If not, get yourself some kind of cap to temporarily seal off the vent if the water gets too high. Just remember to remove the cap before your pond is empty!
My "improved" drawing may not be to scale either. I need to re-look at the length of the 4" pipe to see how tall it is. I recall that the top of the 4" pipe is significantly below my overall dam height + I think it is well below my emergency spillway too. Needs a look see and test when lake is full.
My Emergency Spillway is approximately 10' wide by 5' deep
Looking back, I think my first inclination was right - I dont get this siphon stuff.
But I think I now understand much better, thanks guys.
OK Dan and Jersey,
Unfortunatly my second drawing is fairly accurate. I think the 4" siphon pipe is too tall and will cause a big whirlpool as mentioned above which will take the lake level around the same height as the spillway. Additionally the 4" pipe dosnt have nearly enough holes in it.
I have Vaccum Breaker and doubtful I will ever draw a siphon in current design. The 4" pipe is way too tall. Hello spillway. I'm thinking that I'm going to pull out the 4" and either cut it down or replace with "upside Down U" to make sure I pushing as much water as possible thru the pipe.
Can anyone tell me a way to calculate the difference in thru-put for a drain vs. siphon? Is is 1x, 2x...?
Alligator, I saw a chart a couple of weeks back that showed the difference between a siphon and a plain ol' pipe. I can't find it anywhere now. I thought I saw it on ponddampiping.com but I don't see it there now. You know they say the memory is the second thing to go...
Anyway it seems to me it was about 6 times as much water. I calculated the flow of a 12" siphon (I will have 2 of them) and it was 355,000 gallons per hour each.
I think if you will make a 4" upside down U for your system, you will one day be glad you did. At least have one made that you can pop on there pretty quick.
Thanks for the link Ric, and for the input. I have a little work to do on my Vaccum Braker if it is going to work like a Siphon.
Alligator,
What you have there is a "siphon preventer". I think careful communication with your pond guy will clear up the miscommunication.