I have been trying to set up my bean overflow but it's noisy as hell.
I get the main line to go full syphon and after a couple of minutes, it's totally bubble free and silent. I had to drill a couple of holes just below the surface of the water at the outlet in the sump to ensure that the air was purged to allow the syphon to form, (I read about that earlier in this thread and it worked).
Should not be necessary to drill holes in the siphon in order to get the air to purge. A system that follows the basic design principles of the BA system, does not require such modifications. Only systems that do not follow the basic design principles require band aids to get them to function.
The secondary line has a hole in the cap with a 6mm Pneumatic fitting and hose to prevent it from going full syphon. It is above the water when the primary is in full syphon so air can get in. This line is making a huge amount of noise and is the problem, (it's the one that is noisy at any rate and I perceive it as he problem).
This description is a bit "obfuscated." To be clear, the inlet to the air vent line should NEVER be under water at any time, unless both the siphon and dry emergency have failed. This includes during startup. The inlet to the air vent line should be higher than the inlet to the dry emergency. There is no relation to the siphon.
The emergency overflow is fully open and clear of the water throughout. Obviously not an issue.
Ok. However, is the inlet to the dry emergency high enough to develop enough "start head pressure" in the overflow box to fully purge the air out of the siphon during startup? Water should rise, and flow in the dry emergency during startup, and when the air is purged from the siphon, the water level drops. If this does not occur, or the open channel takes the flow instead of the dry emergency, the system is not starting right, and adjusting the system for proper operation can be frustrating.
If I open the primary fully, it manages to keep up with my return pump on its own and will eventually overtake it and the syphon will break. It will keep doing this until I close the valve to restrict it a bit.
I have tried varying the main syphon's flow rate with its valve to try to mitigate the noise being produced by the secondary line. Small incremental changes to see if there was a sweet spot.
I have tried fully closing the secondary and letting the emergency line take over with the excess. This results in a slight trickle going down and you can hear it trickling into the sump from the open end. It has no problem taking up the slack but it is a little noisy as one would expect, being open to the atmosphere and all.
When I crack open the secondary, it starts all over again. There's a slug of water behind the closed valve, upon opening it fires through to the sump then you get gurgling, bubbling noises coming from the line. Bubbles come out of the line continuously when entering the sump. The hose outlet is below the water so it isn't splashing about, just in case anyone may have thought it was that.
I have tried to incrementally vary it's position but it doesn't seem to help.
Do you think drilling a couple of small holes in the outlet of the secondary as per my primary may help?
I'm a bit stumped at this point. Any help greatly appreciated.
All symptoms of systems that fall outside the basic design principles of the BA system.
My question is, what is not done according to the basic design principles with your system? Most all problems are solved with this system by following the basic design principles that were not followed in the first place.
I have used 28mm pipework throughout.
Swept Tees with threaded caps at the inlet, (hoping they would be less turbulent) :facepalm:
My return is a DC 4000 liter/hour pump, variable speed.
Top of tank is about 5 feet to weir inlet.
But what is the actual drop height or "head height" from surface of water in the overflow, and surface of water in the sump? And what is the head height from the surface of water in the tank, to the surface of the water in the sump. These are the numbers that have relevance. Affects the drain capacity, but not necessarily how high the water level in the overflow box needs to rise to purge the air in the siphon, but it can.
Part of your problem is the size of the plumbing you are using for the open channel. 28mm (not any better than 25mm; e.g. ~1" and 1.1", is too small for a practical quiet Durso. The smallest practical size is 1.25" (~ 30mm. 31.something to be closer,) It is very difficult, to keep a Durso this small quiet.
Also, increasing the amount of air in the standpipe (e.g. increasing the size of the air vent line or increasing the hole size,) will not solve the problem. This allows more air into the line, meaning that less water can be in the line and have it still be quiet. The standpipe has to be < 1/4 full of water, or it is in turbulent flow, (air and water mixing.) This is what creates the noise.