Simple DIY Surge Device


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I recently built an algae scrubber as covered in this thread
In the process I figured a simple way to create an easy to adjust, solid-solid state (no moving parts) cheap and effective surge device. It's a modification of the U tube siphon hose that many people already use. The difference is that this design uses 2 siphon breaks rather than 1. The siphon tube fits down in a small bucket that is continuously being filled from a regular water pump. In my case I'm using a Rio 2100 to feed the surge bucket and I regulate the flow of the Rio with a regular ball valve.
Here is a picture of the entire assembly as it sits on my algae scrubber:

Open the surge bucket and look down from above:

The surge device has two siphon breaks. As water fills the bucket the level rises to where it starts flowing down the tube and into the algae scrubber. Eventually the air is purged from the tube and a full siphon is formed. When this happens water rushes through the tube, overtaking the flow of the pump, and empties the bucket creating a surge. Then the water level falls below the level of the siphon break openings and allows air back into the tube. With air in the system the siphon is broken and this allows water to refill the bucket. As the water level rises it starts the whole process all over again. This design uses no moving parts at all and the rate of the surge can be set by how you adjust the siphon breaks and the flow of the system pump...
Here is a picture of the surge device as it would sit in the surge bucket:

It is made from all 3/4" PVC fittings... You can use larger fittings for higher flow surges.

  • 1 slip coupling

  • 2 90 degree elbows

  • 1 slip tee fitting with a threaded middle section
    1 threaded X slip coupling
    1/4" barb fitting that will fit your airline tubing
    1 o-ring
Join all parts together with regular 3/4" PVC pipe. Cut the pipe just long enough to join all the parts together. When you press the fittings together the pipe is hidden. Use PVC cleaner and glue to fasten everything together.
To attach the siphon to the bucket you drill a hole in the bottom of your bucket and slide the threaded end down with the O-ring sealing against the inside of your bucket. Wrap the threads with Teflon pipe tape and then attach a female threaded x slip fitting (not in the list above) to the threads on your siphon tube. This is the output of your surge device... Now just attach some PVC to the siphon tube to run to your algae scrubber or whatever else you need a surge for.
You need a surge bucket that is taller than the PVC surge device... As the bucket fills, the water level will rise to the top of the PVC tube. The taller your bucket is the more water flow you can use... My bucket is not very tall because this is the first prototype. If I had to do it over I would choose a larger bucket.
To prevent splashing inside the bucket caused by water from the pump, I installed a couple of 90 degree fittings to direct the incoming water flow downward toward the bottom of the surge bucket. This keeps down on the splashing which is important since any splashing can break the siphon prematurely...
Once you get the surge device installed into your bucket and hooked up to your pump, install an airline hose to the barb fitting. Make it form a loop as shown and fasten it in place with a wire tie.

Now it's time to turn on your pump. This device has two adjustments... the amount of water flow coming from your pump and the height of the airline hose that you held with the wire tie. The more water flow you allow into the bucket, the faster your device will surge. Open the ball valve until the bucket starts to fill. As it fills a siphon should start to form as the water level rises to the top of the tube. When the siphon starts it will overtake the pump and the water level will start to go down. Here is where the airline adjustment comes into play...


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You want to break the siphon with both siphon breaks... You do this by adjusting the height of your airline hose inlet. Start by lowering the hose until it is at the same level as the opening on the PVC tube. Depending on how much flow you have coming from your pump, the siphon may not break fully. You'll notice this by the bucket starting to fill up but then reaching a point to where the level doesn't change anymore. What is happening is that the siphon has gotten just enough air in it to match the flow coming from your pump. You don't have enough of a siphon to empty the bucket... but you have just enough siphon to keep up with your pump filling the surge bucket... so the water level never changes.
You need to break the siphon fully but at the correct time. You do this by raising the airline hose. This allows air to get into the system sooner... For a properly tuned system the water will fill the bucket, start a siphon and then drain down. The airline tubing will start to suck air but because of the length of tubing, the air does not get into the siphon hose immediately. So now the airline hose is out of the water, filling up with air but the siphon is continuing. The siphon continues until the water level drops down to the opening in the PVC. Then the system sucks in some air... By this time the air from the airline hose also gets to the PVC tube and fills it with air from the other end. Now the siphon is fully broken and the bucket is able to fill up as it prepares the next surge.
This sounds complicated to explain but it's really much simpler than it sounds. All you do is open up your pump valve and then adjust the airline hose until you get a good surge. That's it. If you want a faster surge (higher frequency) then open up your pump some more. This will fill the bucket faster and start to siphon sooner. You may need to adjust the airline hose after you change the water flow. If you want a slower surge then give it less flow. Adjust the airline hose height here as well.


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I've had some people ask me how quiet this thing is... the way I have mine set up there is some slight noise for just a second at the end but with the lid on and it being in a separate room from my display I don't even hear it.
If someone wanted it to be completely quiet then they could make a muffler for the lid...
In other words, drill a small hole in the lid for air to enter and exit the surge bucket. Then put a muffler down into the hole and it will silence any noise that is coming through the hole.
How to make a muffler:
  • Clean, empty pill bottle
  • 2 small pieces of airline tubing
    super glue
Drill 2 holes in the pill bottle... one on the bottom in the center of the bottle and one in the cap near the side somewhere. Make the hole size such that the airline tubing will slide into the hole and fit snugly.
Next cut 2 lengths of airline tubing so that they are just slightly longer than the pill bottle itself.
Slide both pieces of tubing into the holes you drilled and seal with super glue and let dry. Then put the cap on and slide the bottom hose down into the hole on the lid of the surge bucket.

I haven't built one of these for my surge bucket as it's pretty quiet already but a muffler would eliminate almost all noise from this system if it were that big of a concern.


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This still doesn't make any sense to me...its almost like I'd need to see it in person to understand the schematics of it.