Rainwater Harvesting Wet System Questions

Most gutters overflow away from the downpipe anyway, the G-Ps don't have to be exactly at the high point.

The thicker walled 90 mm stormwater pipe has the same OD as the thin pipe and so the fittings are the same. IPLEX manufacture it.

The thin stuff tends to distort rather than split. Ground movement is the killer.

I did a post (3rd Nov. 11:29 am) about the proper use of PVC solvent and I will link it below rather than repost. A lot of people don't understand its best application and sometimes think that more is best.

viewtopic.php?f=35&t=60317&start=40

Here's the direct link:

viewtopic.php?p=941557#p941557

(next to the date of posts is a small icon, click on that, and the page will reload to that specific post

Thanks for that info Danois. Computers are not my forte.

No problem. Water is not my forte, so I instead try to help with the small and practical forum bits

Hi Guys,

SaveH2O you give some really good advice. Just wondering why you wouldn't recommend using the standard 1,200kpa storm water and you opt for the pressure stuff. Have you had a bad experience?

Hi 4 Pumps.

I think that you might be confusing class 12 PVCu pressure pipe (1,200 kPa pressure rating) with non pressure rated PVCu stormwater pipe.

100 mm DWV pipe is much stronger than 90 mm PVCu stormwater pipe but neither is pressure rated.

The 100 mm PVCu DWV pipe has an internal diameter of 104.2 mm whereas the 90 mm PVCu stormwater pipe has an internal diameter of 86.2 mm. This means that the 100 mm DWV pipe has over 40% more volume than a 90 mm PVCu stormwater pipe. This allows David to use a single 100 mm DWV pipe provided a 40 mm low inlet was also used.

Leaf diverters must be used if a low inlet is fitted.

Hi SaveH20,
Been a while, a long time actually but I'm finally getting around to plumbing the house tank up.
Just after a bit of advice if possible, please.

I want to be able to install one of these sediment trap into my system;

I have attached a plan of the pipe runs to the tank (wet system).



80mmDWV downpipes. 100mmDWV for the west & south runs.
Where the two 100mm runs T together there is only 1m before the vertical riser to the top of the task.
Using a Leaf Eater Advanced at each downpipe & will also be fitting a low level tank inlet off of the riser.

What will be the best location for the sediment trap?
1. Between the last T & the riser into the tank?
2. Or two sediment traps, one in each line before they T together?

Thanks in advance.
Best regards, Dave07

The sediment trap has to be installed to a non turbulent section of pipe to trap bed load, a sediment trap on each run before the intersecting tee is ideal. There would be a lot of turbulence between the tee and the riser. Not good.

If you can order the ICON Leaf & Debris Controllers through the Bunnings special orders desk, you will have a leaf diverter that is superior to the Leaf Eater Advanced.

The Leaf Eater Advanced has a shallow slope mesh the forms a flat recessed debris trap at the bottom. It also gives the falling water no protection from wind plus it doesn't completely drain (retains water to a depth of 9mm) whereas the ICON unit has a steeper straight outer debris filter and a large internal mosquito proof mesh that pulls out from the front for cleaning.

Re the sedinment trap, the diagram shows an inspection junction but you won't need this if you have leaf diverters. It is really a safeguard in case a large object becomes wedged at the pipe reduction but this fitting if fitted would also need an access pit.

The smaller flush pipe/hose could become a tap on a short post but the head will only be the level of water in the tank if a low restriction inlet is also fitted. The smaller pipe discharges at higher velocity and wastes less water. There are several advantages to fitting the additional low inlet:- aerating the anaerobic zone, less retained water in the wet system plus it supplements the discharge rate by operating with more head (the water level in the tank will always be lower than the top of a vertical riser).

Hi saveH2O

I think I've followed your posts but can't find a ratio for head required vs linear distance. We have an old house, about 170 sqm roof area. There is a new 22,700L tank in the back yard with a wet system set up to supply it.

There are 2 sets of 2x 90mm DP going under the house and joining together before increasing to 2 sets of 100mm pipe to travel under the yard to the tank.
The tank is about 45m from the house.

There is some mesh welded inside the gutter at the top of the DP which I intend to cut out, and want to put the ICON leaf & debris controller on the fascia board.

It takes only a small rain event (10mm over 30mins) for the gutters to overflow, so I am losing lots of water (not to mention damage etc).

There is currently 300mm head between the horizontal section of the DP (under the eave) and the tipping point for the water as it enters the tank. Not enough I know. What I am wondering is how much I need?

I am thinking I'll add an extra DP to each side of the house, so I'll have 3x 90mm DP each side, going into a 100mm line across to the tank.

The only other leaf / debris protection currently is the mesh at the top of the tank.

I am thinking about putting an inlet into the side of the tank for the 2x 100mm pipes to lower the discharge and increase head. I know this will sacrifice tank capacity as I'll also lower the overflow, but the tank is in a place where it's not really possible to empty it, move it, dig it in etc.

I'm not sure I understand how the wet system flush would work. Is it a periodic process of opening a valve and emptying the 'wet' system, or does it bleed off over time?

Thanks in advance!
Rob

Do you know your 1:20 ARI. If not, I can look it up if I know the region. This will tell me the minimum flow rates during a minimum intensity 1:20 ARI.

The ICON unit is easily the most efficient unit currently available provided you have head to spare. Unfortunately it is a tall unit that loses about 140mm more head when the spill level is compared to the the Leaf Eater but there are ways to gain additional head.

This is why I get annoyed every time I see 'advice' on Government plumbing websites and from unknowledgeable rainwater harvesting experts that say that wet systems need 300mm.

Good idea.

The pipe fittings (elbows etc) generate a lot of friction loss and their losses are calculated as equivalent lengths of pipe. I would be shocked if the elbows etc on your system have not more than doubled the wet system's equivalent pipe length. Using an online flow rate calculator and calculating flow rates based on visual lengths is a trap for the unwary.

The additional two downpipes (I assume that they will be closer to the tank) will also boost the effective hydraulic head because the water it intersects has already had friction losses but for best efficiency, use a 45 degree rather than a 88 degree junction.

You don't need to touch the overflow because if the tank was tall enough, it would fill to the gutter level (if there was no overflow).

If you have a mosquito proof leaf diverter, you can divert water directly into a tank because the water has already passed through a fine mesh screen. No screen = bad idea.

If you can (it will depend on the tank's construction), have the inlet as low as possible to maximise head.It is also best if you can plumb the inlet pipe to a calming inlet on the tank's floor so that the concentrated flow of falling water doesn't stir up any sediment. If you do, also drill a 5mm air vent hole into the top of the internal pipe.

http://www.rainwater-shop.eu/contents/e ... Inlet.html

You can also have a small supplementary branch pipe plumbed off the riser and into the tank to retain the vertical riser provided the riser's outlet has a flap valve fitted.

You will gain a lot of head by plumbing a lower inlet and this usually allows the additional use of leaf diverters.

A wet system flush valve is archaic because all it does is drain the wet system pipe of some of the captured sediment. This is due to the charged points, i.e. the downpipes and vertical riser(s) being rapidly drawn down, leaving the greater volume of water in the wet system 'sump' to drain by gravity.

A much better method learned from our Supadiverta development program is to fit a DIY sediment trap to a non turbulent section of pipe to continually capture the bed load. The best location for you would be about 5 metres past the last pipe fitting (tee or elbow) before the tank.

Note that if you have leaf diverters fitted, you would use a 100mm DWV 45 degree plain junction and not a more expensive one fitted with an inspection cap.

The method is proven and super efficient.
Bed load (settled suspended sediment) is mostly stationary and only travels in small groups when it does so.
Bed load reconstitutes (becomes larger and heavier) and falls down the 45 degree junction's opening.
The 45 degree elbow is size reduced to increase flushing velocity and reduce the flush volume lost.

Compared to a standard accumulated flush system, the water retained in the wet system is cleaner and there is considerably less yield loss.

Once you have stopped the overflows and you have higher yield, you will also need to examine the overflow meshed outlet capacity but this is easy to substantially improve.

Bit of reading to do...