Breaking the siphon on a large pump?

JC Pollman

Premium Member
I am planning on using a large pump (at least a dart) for my return and am concerned about siphoning the tank into the sump when the electricity fails. A couple of issues:
1. I intend to route the return flow to the bottom of the tank, so I guess I have to run the pipes above the water level first?
2. The pipes will be 1.5 inches diameter, so I am concerned a small air hole will not work well, and if I use a large air hole, too much water will be lost.
3. This will be a plywood tank, so drilling holes will not be an issue.

Thoughts?

JC
 
Check valves will fail. NOT a good idea. Drill a hole or two in the return line just below the normal water line in the main tank. This will break any siphon if/when the power fails.
 
That is a dangerous setup, for sure. Do as Freed said, but those holes MUST be kept clear. Even a snail on them at the wrong time will allow the siphon to be created.
 
actually i have 2 1 inch return lines that go up and over the tank, about an inch below the water line i drilled a hole in both of them about a little less than half inch, i turned the pump on and was surprised that i couldnt feel alot of water coming out of the holes,so dont think that you wont have any water pressure coming out the bottom part,but i only have another 2 inches of pipe below these holes. I also started out with small holes and kept on testing it untill i felt comfortable that it would break the siphon
 
I really don't know how reliable it would be as I've never seen this before, but an idea would me to T off of the return line. Put a check valve on that so its closed doing normal pump operation (so it cant blow water into the tank from that T. Now when the pump is off it would cause a vacuum in that line and cause the check valve on the T to open allowing lots of air to enter and break the siphon. That would also allow for easy testing to. Alls you would have to do is turn the pump off to make sure the valve still opens. With this setup the check valve would normally be closed rather than open.
 
<a href=showthread.php?s=&postid=14339388#post14339388 target=_blank>Originally posted</a> by Freed
Check valves will fail.

Because of calcium build up, etc.
 
heres a quick pic of my idea:
172523antisiphon.JPG

The only failure option I can see with my idea is if the check valve ended up stuck shut (even with the siphon vacuum effect). Most of the time they end up stuck open though from calcium buildup and whatnot ....
 
<a href=showthread.php?s=&postid=14339996#post14339996 target=_blank>Originally posted</a> by coralfragger101
SEVERAL siphon holes AND make keeping them clean part of your routine maintenance.



I have 2 syphon break holes on my return and as coralfragger said this must be a part of week to week maintenance.
 
The idea of a T with a check valve in headed in the right direction.

Instead, have the piping off the T be 1/2" to 3/4" and put a ball valve on it, and then direct the piping into the overflow so it's out of sight.

You can adjust the ball valve to allow a small amount of water to flow, and this will then quickly break the siphon in the return system when pump flow is shut off, while allowing you complete freedom for final placement of outlets below the waterline.

A few points.

1. Run the outlet someplace where you can visually check the water outflow when doing weekly tank maintenance. this is a more positive check then wondering if a check valve will function the next time the pump is shut off.

2. On larger systems, do this x 2 after you split the return piping, for redundancy.

3. Play with how far the ball valve is open to find a balance between how much water is bypassed into this path, and how quickly the siphon is broken.

4. Cycle the ball valve fully on/off completely once a month to knock any build-up off the valve surface

5. If you leave the return point above the surface of the water, the siphon break is instantaneous. You just have to play with how high, at what angle, etc to silence it.

All three of my bigger tanks have been runnig like this for years, and it's so nice to have the instantanous siphon break.
 
<a href=showthread.php?s=&postid=14340573#post14340573 target=_blank>Originally posted</a> by MMM33732
heres a quick pic of my idea:
172523antisiphon.JPG

The only failure option I can see with my idea is if the check valve ended up stuck shut (even with the siphon vacuum effect). Most of the time they end up stuck open though from calcium buildup and whatnot ....
I forgot the mention, the check valve wouldn't be a small one for airlines, it would be maybe 1/2-1.5" whatever you feel is necessary and opens easy so it could let lots of air in fast.
 
I use a tee in my return line, but not for a check valve. I use a small piece of airline tubing from the tee and then direct that back into the overflow. It runs a small amount of water through it constantly and no animals can get to it. When I cut my pump off it instantly breaks the syphon with no drain back. ;) It looks similar to your drawing, but the tee is turned up and not down and it has airline tubing connect with a nylon fitting.
 
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