Plumbing Genius ( Rainwater) required :)

While I have an engineering background, I didn't think this question was all that unreasonable, but have not been able to get the answer I want

We're shortly building a new house in suburbia (in SA) and of course a rainwater tank is mandatory.

99% of rainwater tanks seem to be using the Davey "Rainbank" system to automatically switch between the rainwater tank (if available) or the mains water when rainwater is not in the tank.

The system will be plumbed into the house for toilet and washing machine use.

A new toilet uses around 6 litres / flush.

So, there is water pressure (stored) between the pump and the toilet float valve, monitored by a pressure switch.

Flushing the toilet releases the pressure, the pressure switch sees the drop and commands the pump to run until the pressure recovers, caused by the toilet valve closing.

OK...... flush the toilet, pump runs, pumps six litres, pump stops, repeat many times a day.

Davey also sells various size accumulators, "Pressure tanks".

SO............

I phoned up one of the largest rainwater tank / Davey pump suppliers in SA and outlined everything above and said ..................

"Can I just put a large, or a couple of smaller, accumulators in the system so that the pump doesn't stop-start so often."

Theoretically (discounting losses) if I put say a 60 litre accumulator in the system, and the toilet is 6 litres, the pump should only run every 10 flushes.

The rainwater dude thought this was a great idea, but didn't know if it could be done, and suggested I contact Davey Customer Service.

I was like......."Hey, every new house in SA (Australia ??) has this issue and I'm the first to ask this question....WTF ??"

So, I rang Davey Customer service.

They too had never heard of something this revolutionary

The dude there went and asked his mate and came back with "No, Not possible".

WELL........THAT SOUNDS LIKE A CHALLENGE TO ME

I don't believe that "It can't be done".

Any thoughts ??

Thanks,

P_D

it should be possible but the size of the pressure vessel would need to be very much larger than 60L (Davey probably don't do one this big) You are maintaining the water pressure by compressing a volume of air but there is a limit to how much the water pump can increase the pressure.

I haven't got the figures to do the maths but you are probably looking at a couple of hundred litre tank.

Hi P_D

I'm a long time lurker tho 1st time poster (about to OB a 60sq place hence the name )

I am reader of the renew magazine. "sometime" in the past 12 months they had an article on exactly this. Unfortunately I seem to have filed that copy.

The writer of the article found the same answers as you did when talking to the pump suppliers and from memory he did two things

a) installed a larger pressure tank (which you have already worked out!)
b) changed his pump with an electronic pressure switch over to a pump with a manual pressure switch that can set both the upper AND lower pressure ranges. Apparently with the electronic ones, you could only set the upper range.

This was the only bit of info on that article online I could find.

http://renew.org.au/sustainable-products/product-profile-want-to-make-your-pump-last-longer/

Good luck!

Tim

the davey pump and onga pumps which are commonly used are generally good quality pumps and designed for stop start. They are not petrol engines which reach there peak when warmed up and require oil to flow through pistons to reduce friction.

If you still dont like the idea of this why do you just raise you water tank a little. Install very thick pipe and gravity feed your cistern. It doesnt matter if it takes a bit longer???
Or how about include this with a larger cistern that has storage of say 20litres. Then it could do about 4 full flushes. So even it it takes 10 minutes to fill you have plenty of buffer.

Providing a higher tank would be OK for the toilet only but the problem would be the washing machine...the inlet control valves need a fair bit of pressure before they operate.

Hey pepsi_drinker,

How did you end up going with the pump/pressure tanks? I have been grappling with the exact same problem - I want a RainBank to save the hassle of switching back and forward if the tank runs dry - but at the same time I want a large pressure tank so the pump is not forever 'cycling' (stop/start).

I have the article from renew mentioned above, where it talks about pressure tanks. The system involved there, I believe, didn't have the complication of the RainBank though.

I'd be interested if you found any further information on *how* it could be done.
Let me know if you want a copy of the article and I will dig it out

There has been no movement recently due to our (potential) builder shutting down over the Christmas break.

I did however get an email from him a couple of days ago with "V2" of our plans, so things will start to happen now he's back at work !!

I agree, something like this shouldn't be rocket-science, I'll email Davey this afternoon and ask the question directly, in writing, to them, I'll also point them at this thread.

I'll post back as soon as I hear something from them.

And as an aside, it shouldn't make any difference, but before the Christmas break, the last word we had with the builder was that we're considering an underground tank, so unless we dig a really large hole to put the house in, any form of gravity feed isn't going to be an option !!!

Cheers,

P_D

I fitted a larger pressure tank to my pump when I lived on tank water. The pump was a davey and had a manual pressure switch. Most pump/irrigation shops on Brisbane knew very little about actual pump applications and had no 'real' experience in the market, as soon as I went to a shop in a rural area, I got better pricing and staff who knew exactly what I wanted to do and how to do it.

My father in law has a Davey pump for his toilet/laundry and on the pump housing there is a bung that holds a small spring/valve type thing. If we were to run a pressure tank, then the spring bung thing needs to be removed for the switching to allow for the tank pressure.

Thanks phippsy,

The issue is that for (most / all ?? ) new houses a rainwater tank is mandatory, and 99% of people seem to also fit a "Davey Rainbank", or equivalent, and we're trying to get the accumulators to work with the Rainbank.

Cheers,

P_D

I came across this thread by accident when Googling another subject matter. The questions asked are simple but the thread was posted in the wrong sub forum (new home).



RainBanks are fitted because the larger water tank companies that do the new house installations usually have a commercial association with Davey. I personally do not recommend the RainBank, my favoured automatic option is the clever Acquasaver that works off the mains water hydraulic pressure.

http://www.acquasaver.com.au/

The Plumbing Code of Australia also allows bullet proof and much cheaper manual systems that require (simple) manual switching. It is rare for a new home owner to be told of their cheaper and bullet proof options.


6 litres for a full flush, 3 litres for a half flush.



The Davey RainBank's Installation and Operating Instructions state:
Do not use pressure systems or accumulators with RainBank®.