Browse Forums General Discussion Re: Rainwater tank pipe diameter 2Jun 11, 2021 12:23 pm 3in1 Supadiverta. Rainwater Harvesting Best Practice using syphonic drainage. Cleaner Neater Smarter Cheaper Supa Gutter Pumper. A low cost syphonic eaves gutter overflow solution. Re: Rainwater tank pipe diameter 4Jun 17, 2021 6:03 pm You need to increase the discharge capacity and this includes having an overflow pipe on tank 1. HandyManny Plumber (builder) has advised overflow is normal in heavy rain, im not convinced. And you are right. Having tanks in a stormwater system overtopping with about 470 lpm going to ground during a minimal 1:20 ARI is not right by any stretch of the imagination. The plumber either has no idea or is evacuating terminological inexactitudes. (Thanks for that Winston)! The person who designed the system also lacks required knowledge. Best practice would have incorporated a settling tank system with a single 150mm vertical riser and an internal 150mm standing bellmouth on a single 100mm overflow pipe to supercharge discharge capacity during a high intensity rain event. To learn how little the person who designed the system and the plumber know about the art, ask them "What is the minimum flow rate entering the tanks during a 1:20 ARI?" and then ask them "What is the discharge capacity of the single 100mm overflow pipe and what flow restriction does the mesh present?". Unfortunately, rainwater harvesting systems designed with insufficient overflow capacity are not uncommon. HandyManny 100mm Discharge on tank 2 is at the maximum height. There may be 125mm above the overflow fitting's invert so those figures I posted last time should be used but the mesh will reduce the discharge flow rate from about 343 lpm to about 275-280 lpm and much more if the mesh has started to gum up. It is difficult to keep the overflow mesh perfectly clean. Like ⋅ Add a comment ⋅ Pin to Ideaboard ⋅ Like ⋅ Add a comment ⋅ Pin to Ideaboard ⋅ TANK 2 The 100mm overflow pipe would satisfy this tank's requirement if the outlet was unmeshed. I suggest removing the mesh and fitting a dual meshed air gap to the vertical overflow pipe. https://www.youtube.com/watch?v=sE8IChfIFCA P.S. NOT impressed by the demo tank's overflow design! TANK 1 Fit additional 100mm overflow pipe. Remove mesh and fit an air gap to the vertical overflow pipe. This will provide a total overflow capacity from the two overflow pipes of close to 690 lpm. With the roof space diverting a minimum 746 lpm during a minimal 1:20 ARI, the balance line will send some water to tank 2 with tank 1 having an additional overtopping head but a new overflow on tank 1 requires an absolute bare minimal discharge capacity of 400 lpm. I suggest having more. I would as a minimum fit an additional 50mm unmeshed outlet and connect it to a DWV 100mm x 50mm 45 degree reducing junction above the air gap. This is easily done when also fitting the air gap. With the 50mm outlet at the same invert height as the 100mm outlet, it would have a discharge capacity of 1.65 lps (99 lpm) with 125mm of water above the invert. To supercharge the new 100mm overflow pipe's discharge capacity, just fit the overflow outlet a little lower down and fit an internal 90 degree standing elbow. A vertical (standing) pipe drains more efficiently than a horizontal one, with 125mm of water above the crest, a 100mm vertical pipe will drain at 7.38 lps (443 lpm). Heating and bellmouthing the pipe's 'reservoir wall' even a little will further increase the pipe's overflow capacity, for example, a 150mm bellmouth will discharge at 7.51 lps (450 lpm) with only 40mm of water above the crest! Bellmouthing also allows Tank 1 to have a higher (delayed) overflow level than Tank 2. You can see in the photo below why the outlet hole has to be drilled lower down but note that it is a big tank. Like ⋅ Add a comment ⋅ Pin to Ideaboard ⋅ A couple of additional notes: The builder or plumbing engineer will have almost certainly used the NCC (Part 2) roof drainage regulations because they are laxer than the Australian Standards. The NCC Part 2 has the regulation pasted below. "3.5.3.5 Downpipes — size and installation Downpipes must— (a)not serve more than 12 m of gutter length for each downpipe; and (b)be located as close as possible to valley gutters; and (c)be selected in accordance with the appropriate eaves gutter section as shown in Table 3.5.3.2a to Table 3.5.3.2c". If you look at downpipes 4 and 5, there is one heck of a distance between them and the gutter length serving those two downpipes could/would exceed 12 m. The upper roof downpipe that discharges to the garage roof drains a concentrated flow of water to the end of the gutter furthest away from where the downpipe is located. This is poor design, particularly when the tank 2 top meshed inlet is close to the gutter's mid point where the downpipe should have been fitted. 3in1 Supadiverta. Rainwater Harvesting Best Practice using syphonic drainage. Cleaner Neater Smarter Cheaper Supa Gutter Pumper. A low cost syphonic eaves gutter overflow solution. 18 90477 DIY, Home Maintenance & Repair But if it is a ground level open pit, then it is not a charged system. No surprises there. The pipes have obviously been altered and there would be a reason for this.… 3 31280 Grate, thank you! RexChan if thats the reason i could sleep well without thinking about additional cost. But 1st i'll need to read about NRV cleaning/replaing stuff. I… 7 31149 |