need help with overflow pipe heights

JamesThomas · Jan 15, 2019

So the more I read, the more I confuse myself. Ive successfully mounted at Marine Modular 1600 overflow.
Id like to use a screen drain for my main, and Ive constructed the secondary. the emergency can be cut to any length.
SOOO, my question is How tall should the emergency pipe be? Just below water level in tank? The secondary is the tough height question? How tall should it be and will just the screen drain work for main?

dugthefish · Jan 15, 2019

The higher your can run the water level in the exterior side (higher emergency drain), the quieter it will be. Mine is like .5-.75" below the top of the compartment.

sbash · Jan 15, 2019

If I understand your inquiry correctly. You have three overflow pipes (from left to right) Emergency, Full Siphon, Secondary.

So, let's discuss each one:

Emergency: Your emergency overflow should be dry all the time (unless, of course, an emergency happens). At the very least, it would be above the water level in the overflow, possibly even above the tank's standard water level.

Full Siphon: Your Full Siphon overflow is the powerhouse, most of your water will be moving through it. This line usually requires a valve to establish the perfect siphon. The siphon needs to terminate below the water level. Ideally it would be high enough to minimise the amount of water it drains from the overflow chamber if the pumps are shut off; this is especially important with a corner overflow (unless you have lots of head room in your sump).

Secondary: The Secondary overflow essentially catches the left over water from tuning the siphon. The secondary also sets the water level in your overflow. Commonly the secondary is configured as a Durso overflow, which gives the added advantage to set the air intake (tube) just below the emergency; this creates a siphon if the water level gets higher than it should.

You can make the secondary adjustable (i.e. see your picture) by not gluing the intake elbow. Then you simply rotate it around to set your water level (essentially turning the elbow into a weir).