Surging Durso

[Ira]

The water is going to take small bubbles of air down the pipe with it. Eventually that will be enough to turn it into a siphon.

[chimera]

but surely the pipe going down to the sump must be full to suck water down? i run a 40mm pipe down, no surging at all in the overflow with durso, is this because its large enough to cope with the flow of water? (in other words it also has sufficient air in the pipe?) i see what you mean about the water dropping to the inlet - only when the pump is turned off AND their is no air in the pipe. so there would need to be a hole in the U bend

[Ira]

No, the entire pipe doesn't need to be full of water to siphon. And the pump doesn't need to be turned off because, like Reef says, it's unlikely the return pump could pump water as fast as the siphoning overflow will be sucking it out.

And your current durso, plug the air hole and see what it does. After a bit it will suck all the water out of the overflow until it hits the inlet and lets air in.

[chimera]

damn 8)

[Ira]

from the durso web site

"Flushing Effect: A commonly reported problem when first installing standpipes is what I call a flushing effect. The water level in the chamber bounces up and down at a slow steady cyclic pattern. This is different than the issue above where the water level stays to low. This issues typically is not caused by the size of the air-hole in the end cap. The flushing effect is almost always caused by back pressure in the drain line. Typically the back pressure has two main causes:

Drain pipes in the sump being submerged below the water surface to far. Ideally you just want the drain pipes submerged about an inch or two. Just enough to reduce the splashing noise in the sump.

Any loops or dips in the drain lines if using flexible tubing. If using hard PVC pipe for the drain lines make sure they always have a slope to them, don't make them perfectly horizontal or perfectly vertical.

The flushing effect works like this: Back pressure in the standpipe prevents air in the pipe from exiting the drain line. Instead of exiting the drain line, the air bubbles try to rise in the pipe slowing the rate at which the pipes drain. The water level in the chamber then rises. The increase in the chamber water level adds pressure to help clear the air from the pipe. Once enough water pressure exists in the chamber to overcome the back pressure, the air is literally is "burped" out of the drain line which crates a sudden rush of water. This is displayed as a rapid drop in the overflow chamber water level. This cycle then repeats itself over and over as the back pressure builds and gets purged. "

I was just thinking about this...I wonder if it might not be part of my problem? Mine exits maybe 9" below the water surface. It looks like the only way I can get the water level stable is having the water level in the overflow extremely high, basically at the same height as the rest of the tank. Maybe if I cut a bit of length off the pipe to the sump I can get the siphon in the durso turned up a little more and get the water level in the overflow a bit lower which would also help skim off the surface of the tank?

[cookie extreme]

any reason why this wouldn't work? kind of like an upside down durso but without the requirement of air, so sort of full syphon but without the tap

thats called a ful syphon. put a valve in and it works a bit better

[chimera]

i like the fact that full syphons are fully silent (because the air is removed from the plumbing which is what creates the noise) the thing i dont like about a full syphons is they have more risk (and no matter what layton says more risk than durso) you are in essence restricting the overflow pipe by ball valve down to the minimum possible size that will allow the syphon to suck water only (and not too big that the water lowers so far that it starts to suck air) so it takes alot less to block the pipe and flood the tank. ok, so you add an overflow cover,... but baby snails can get through overflow combs, baby snails can live in overflows and grow, baby snails turn into big daddy snails that can block pipes at least with the durso you can go with a large pipe and still maintain a large enough surface area. i run 40mm down, i could stick a snail in the pipe and it wouldnt do anything to the flow, plenty of room in the pipe to spare. so ok, build extra pipes into the syphon overflow for redundancy, but that then indicates a design flaw in the full syphon - having to add a safety factor, compensating for something that may not have been adjusted correctly or because it gets blocked.

ultimately its a trade off of course between complete silence with FS versus slightly noiser durso. there are clear pro's and con's of each.

however i'd really love a combo of both, dead silent like the FS yet safer and lower maintenance like the durso. also something that does not require a ball valve or any need to make adjusments. can it be done? if there is no other easy solution, then i guess full syphon WITH backup pipe as redundancy (which is the only way i could install it without worrying about flooding the hose ) is the best way for *complete* silence

[Ira]

You could make your sump air tight and turn it into a giant cannister filter.