Dealing with stalled downpipes

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neb

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#3203784 6-Mar-2024 14:16

Just found my notes on this, for people who asked about the capacity:

Front gutters are Marley Magnum which is upscaled Typhoon, Magnum is commercial-grade 189x110mm while Typhoon is residential-grade 133x100mm but just that small change takes it from 87lpm to 250lpm, 40mm/hr of rain is 100lpm off the roof which overwhelms the Typhoon.

The gutters have never overflowed since switching to Magnum while they often overflowed with Typhoon, it's only the downpipe that has caused problems.

tweake

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#3203838 6-Mar-2024 17:30

neb: Just found my notes on this, for people who asked about the capacity: Front gutters are Marley Magnum which is upscaled Typhoon, Magnum is commercial-grade 189x110mm while Typhoon is residential-grade 133x100mm but just that small change takes it from 87lpm to 250lpm, 40mm/hr of rain is 100lpm off the roof which overwhelms the Typhoon. The gutters have never overflowed since switching to Magnum while they often overflowed with Typhoon, it's only the downpipe that has caused problems.

do you what the roof size is roughly and the pitch? marley have the cheat sheet for the downpipe but its based off roof size.

the simple problem is 100mm/hr rainfall is the (auckland) standard. but those big rain events are around 150mm/hr. so your Magnum gutter is only just ok with not much capacity for big rain events. btw thats not accounting for slope, length of gutter, or downpipe placement.

neb

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#3208149 19-Mar-2024 19:14

Here's the current fix attempt, just a 90->80mm reducer dropped in above the overflow point.

This is just to see what happens, it's acting as a flow constrictor but it's also going to push the overflow location upstream a bit to the expansion joint at the outlet so it remains to be seen how much will force its way out there as opposed to flowing along to the next downpipe.

neb

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#3209979 23-Mar-2024 21:48

Well, that didn't work. Just had a bout of heavy rain and the downpipes still stalled despite being restricted to 80mm inflow to match the 80mm leaf eater inflow. A temporary kludge of dropping a 100mm pipe across the outlet to force at least some of the water along to the second downpipe didn't help much, it raised the water level in the gutter a bit so a bit of it would have gone to the second downpipe, but the first one was still stalled until the rain eased.

The weird thing is that what's coming down through the leaf eater is a gentle flow equivalent to maybe the output of a garden hose at full flow, not an 80mm pipe worth of water. I'll put a camera up it when it's dried out a bit but AFAIK there's no constriction or blockage anywhere, it's just not flowing down at any useful rate.

Next trick will be to see if there's any of the Magnum guttering left over and cut out a sort of aquaduct to lay over the outlet, so the water level in the overall gutter has to rise to a certain point before it overtops it and goes down the first downpipe, with most of it flowing on and down the second downpipe.

neb

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#3214773 5-Apr-2024 18:40

Finally sorted it, I ran a borescope camera up it and saw that, despite trying to clean it out with a hose, there were still more leaves up there, so I went through many iterations of { leaf hook, hose, camera }, which yielded this:

Finally I poured a 5L bucket of water down it, of which 90% went down the pipe and 10% went down me, and ran the camera up it again, which showed an almost-clear pipe except for this:

That's most probably a corner protector from one of the solar panels which got dropped on the roof, missed because it was transparent, and at some point washed down into the downpipe and got stuck there, catching leaves that were washed past it until enough built up to block the downpipe.

Now I just need a test load of heavy rain to see whether the problem is solved.

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