Fish Teen, Feel free to speak up.
Surge devices are done using either gravity or mechanical valves.
Gravity is great, because there is nothing to fail. It always works, and nothing can break in the system to cause an issue. Gravity systems down fall is you have to push all the air out of the pipe - which causes bubbles. There is usually a burp at the start of the surge, when the water finally overwhelms the air and pushes the air out of the pipe.
And then when the surge finishes there is a flush noise at the end of the cycle when the water falls below of the intake in the surge tank.
The costs involved with a Gravity surge is a pump, a tank, and a minimal amount of plumbing parts that can be found a home depot.
My surge is 26g, it sits on a second story above the tank. I engineered a muffler system for the pipe, and my surge makes no noise inside the house. Outside where the surge tank is, when the surge finishes it sounds like a wave breaking on a beach.
With 2" plumbing, all sweeps - no elbows, a 10'+ drop, 26 gallons falls in about 6 seconds and is a dramatic effect/impact in a 400g reef.
Now with Mechanical, you can overcome the bubbles, which is an issue with gravity. But now you add bits and parts that can fail. You need float switches, timers, overflow sensors, and the mechanical valves.
Major difference out of the gate, is the costs of the Actuated ball valves. Depending on the plumbing size the typical Spears / Hayward and Jandy are pricey toys.
But outside of initial cost, and longevity they bring their own issues. First off depending where your surge tank is located (Mine is outside) the valves make noise. The sound is like a plane starting a jet engine (not loud but that kind of droning noise).
Plus the cycle time of the ball valves is slow. Because they have to be able to open and close valves under heavy pressure they are slow and torque based. Some valves have a cycle time of 30 seconds from open to close.
That means the surge starts as a trickle and slowly builds up flow until the valve is fully opened... 30 seconds of draining water. You're going to need a very large surge tank, so that by the time the valve is fully open there is still enough water in the surge tank for there to be something to surge.
Now when that surge tank runs out of water its going to pull air at the end of its cycle, perhaps depending on your plumbing even a vortex, like you get when draining a bath tub, so you are still going to get air bubbles at the end of the surge cycle.
So the way to avoid this is to close the pipe before the surge tank runs dry. So now you have to cycle the valve again - another 30 seconds while still having enough water in the surge tank to keep water in the plumbing and not air.
Even if you had a gigantic surge tank, and set up a timer system where the valves open and close. Then next issue you have is longevity. Actuated ball valves are not really designed for continuous use. So depending on your flow rate into the surge tank.... how frequently are you going to need the valves to cycle.
My second story tank is filled with a Rio Hyperflow 32. And my surge cycles about every 90 seconds.
Now, pneumatics would be the valve of choice because they have very quick response times. So they can open and close in the matter of a second or two. Which is the perfect on/off time for a surge tank. To keep you bubble free in your display tank.
But the pneumatics also have their issues. One is the cost. Two, you need a compressor to keep them supplied with pressure. Three the noise when they cycle. Four. Because they operate so quickly, the water flow in the plumbing changes quickly and it can cause your plumbing to Slam... Loudly like a shudder in your house.
I am sure there are many threads of people who have done different surges who all claim theirs is the best.
But before you implement one, you need to really try to see it in action. And then I would recommend building a mock-up to see if that design works for you. People who have taken the time to design a surge tank for themselves are very proud in what they have done, and will usually overlook the downsides to their design --- bubbles, noise, shuddering plumbing.
And then there is the wife factor...
In most applications you can't run a surge system 24/7... They all make some bit of noise and depending on the location to where you sleep or live your life the surge tank needs to be on a cycle around your waking hours.
