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PostPosted: Dec 11th, '19, 19:50 
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Joined: Dec 11th, '19, 18:02
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Tell me I'm missing something please (if I am). I've been busy trying to troubleshoot my Cetus installation. I have some more fiddling to do but my presumption is that the unit is mounted too high and that the weir bottoms out before I get adequate flow for my pump. If so, my options would be to raise the pond level (not possible), lower the sieve (difficult secondary to the concrete floor in my filter pit) or to custom-build a new unit similar in concept to but different in dimensions than the Cetus unit. In doing my research on DIY and commercial sieves I have come across two basic designs. The first (Cetus) utilizes a floating reservoir/weir that adjusts to the pond level and would appear to be preferable in that if it floats high enough it should shut off all the water from the pond without any leakage into the lower compartment. It's downfall appears to be the bellows needed to feed it water from below yet still allow it to adjust readily to the water height. Many people have reported problems with deformation of the bellows. Plus, the bellows itself is expensive to purchase and engineering watertight connections from below seems at least somewhat problematic. The second concept is that of the Ultra-Sieve III. With it the reservoir doesn't float up and down (so a bellows isn't necessary) but rather there is a floating dam that adjusts to the pond water level. I haven't seen a unit in action but it would seem to me to be probable that it would be difficult to make a DIY unit that would be tight enough not to leak around the edges of the dam yet loose enough to ride up and down easily and not bind.

My brainsquall (that's a small brainstorm) follows. Why not feed a floating Cetus-style reservoir/weir from above with a siphon, as in the following diagram? If the depth of the weir reservoir is sufficient and the down-limb of the siphon is the right length to keep it underwater at all times then there should be no effective limitation in draw-down due to the length of the bellows and no problems with binding and friction as the unit floats up and down. Plus, one could make a unit of just about any size desired. Furthermore, engineering the thing would appear to be almost trivially simple. There's one less pipe that needs to pierce the housing and no fancy fittings that have to be made waterproof. No special stents or supports would be needed to protect against bellows deformation. The floating reservoir should be easy to make out of whatever is available (acrylic, etc.) as it's just a box. Unless I'm missing something the whole unit could be easily fit inside a 55 gal drum, which is cheap. My schematic is oriented in the "standard" Cetus/Ultra-Sieve fashion, with the water flowing over the weir and down to the right onto the wedge-wire, but I can't see any reason why the siphon can't extend farther to the right before descending, thereby allowing the weir to overflow to the left and allowing more space for the wedge-wire sieve beneath it. If this works one could build a sieve for little more than the price of a few fittings, some acrylic and the wedge-wire (hardly cheap but a lot better than $1200 for a Cetus). What do you all think?

The astute observer will wonder how I propose to fill the siphon. With the pond and weir/reservoir full the incoming knife valve can be closed and the end of the siphon temporarily capped. Then the valve at the top of the siphon loop can be opened and the loop can be filled from above. After doing so this upper valve can be closed in an airtight fashion and you should be good to go (after opening the knife valve and removing the temporary end cap). I'm sure there are other ways to do accomplish this but at least this is simple.

I'm pretty certain I'll try something like this if I'm unable to rectify the situation with my Cetus. At this point I already have the Cetus wedge-wire and I can utilize it in this new application if necessary. Please let me know if any of you can see any glaring reason why this might not work. I only thought of it today so it hasn't withstood a full analysis but as it is... I'm excited!

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PostPosted: Dec 15th, '19, 13:19 
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Any chance you have photos of your current weir? Not sure how this functions entirely.


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