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AllanS Regular Member Joined: 05/06/2006 Location: Posts: 67
Posted: 08:40pm 23 Jun 2011
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My hot water is turning rusty. Time to spend $1000. Again.
Suppose I isolate the cylinder using plastic pipe instead of copper. Then connect the - of a small charger to the tank and earth the +. So long as I can keep the tank at about -2V, it will never rust. I'm on rain water, so I shouldn't lose too much voltage through electrolysis. I wonder what it would cost in power?
Anyone got experience in cathodic protection? If this could double the life of the average HW cylinder for very little cost, installing them would make a nice little business...
RossW Guru Joined: 25/02/2006 Location: AustraliaPosts: 495
Posted: 11:41pm 23 Jun 2011
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Serious question: have you considered just using a coil of copper pipe in your "water heater" as a heat exchanger?
That way, you can isolate the actual water heater water - add anti-corrosion compound to it if required - but once you get all the oxygen out of it, it shouldn't rust anyway.
You hot water will go through the copper pipe - and won't rust either.
Its what I've been doing here ever since we built, and works great. Has other benefits too - like you never suddenly run out of hot water - it just gradually cools down.
AllanS Regular Member Joined: 05/06/2006 Location: Posts: 67
Posted: 12:06am 24 Jun 2011
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Hi Ross,
Brilliant! A coil of copper pipe will cost a good deal less than a new HW unit... The tank doesn't need to be pressurised either, and can be made to last virtually forever... This sounds like a winner. What length do you need to get a fair exchange of heat? Do you get any annoying water-hammer effects with all that loose piping?
Cheers.
Barry T Coles Senior Member Joined: 30/07/2009 Location: AustraliaPosts: 109
Posted: 12:36am 24 Jun 2011
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Hi Allan
May be able to help you out here, I worked as a Cathodic Technician for some years in the water industry.
Some things I need to know; what type of heater is it, IE storage tank heated by solar, sun, gas, or is it an instantaneous type like gas fired up on pressure.
Most storage systems have an anode in them that can be easily replaced by the average tinkerer if you know what type of anode is needed (usually Zink for average water systems)another important thing to look at is your house earthing, if it is connected to your water supply like a lot are then you can get earth leakage that will effect your system.
I won’t make any assumptions until you get back to me but I don’t recommend you try inducing a current into the system; by doing that you are trying to set up an impress current system that needs constant monitoring & you can accelerate the corrosion situation.
Cheers
Barry
I need to learn from the mistakes of others.
I dont have the time to make them all myself.
AllanS Regular Member Joined: 05/06/2006 Location: Posts: 67
Posted: 12:51am 24 Jun 2011
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Hi Barry,
It's a pretty standard (Rheem?) mains pressure electric HWS. I reckon there's a good chance I'm earthed somewhere via my water pipes. The prospect of accelerating corrosion doesn't sound good...
Barry T Coles Senior Member Joined: 30/07/2009 Location: AustraliaPosts: 109
Posted: 02:52am 24 Jun 2011
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Hi Allan
To easy my friend; have a look at the top of the heater tank & you should see 3 rubber grommets, the large one in the centre covers where the anode is screwed into the tank.
You will see that the hex head of the anode is colour coded to the TDS of the water.
There are no electrical connections to the anode as it is a sacrificial type; to replace it you would need to take the same precautions as you would for working on the hot water pipe work of the house IE turn of the power, water inlet & drain the pressure by opening the pressure release valve, you can then remove the old anode & connect the new one or get a plumber in to do the replacement.
Heres a link to the owners manual.
http://www.rheem.com.au/downloads/Manuals/installation%20ins tructions%20-%20Rheem%20electric%20domestic%20-%20121996%20R ev%20E%20-%202010%20July.pdf
Sorry mate I couldnt get the link to work but if you copy & paste the above addy into the web header it will take you there, page 11 talks about the anode & page 12 gives water quality advice TDS.
Cheers
Barry
I need to learn from the mistakes of others.
I dont have the time to make them all myself.
AllanS Regular Member Joined: 05/06/2006 Location: Posts: 67
Posted: 03:40am 24 Jun 2011
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HI Barry,
I didn't know HW systems even had a sacrificial anode. I just assumed built-in obsolesence. I'll have a look and see what can be done, though things might have gone past the point of no return...
Cheers.
RossW Guru Joined: 25/02/2006 Location: AustraliaPosts: 495
Posted: 04:11am 24 Jun 2011
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In my system, I ran a full coil (18m). The temperature difference I see between the water temperature in the tank, and the water comming out of the heat exchanger, while having a shower or the washing machine is filling, is barely degree or so, near as I can tell. This morning, I had cold water going in at 13.3 deg C, and the hot water comming out at 53 deg C - the water in the tank was 55 deg C. I suspect you could get by with less pipe.
Never seen, heard or felt any water hammer with this system.
As you say - no need for pressurised tank or any of the (potential) dramas that implies. (pressure relief valves etc)
nishka Newbie Joined: 20/06/2011 Location: New ZealandPosts: 7
Mechanic, Engineer, Electrician, Thinker, Tinkerer, Backshed Inventor, Hermit and general mad bastard ;-)
AllanS Regular Member Joined: 05/06/2006 Location: Posts: 67
Posted: 10:20am 24 Jun 2011
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Sounds good, Ross. I'll let you know how it goes.
Cheers.
GreenD88 Senior Member Joined: 19/05/2009 Location: United StatesPosts: 104
Posted: 01:17am 28 Jun 2011
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Sacrificial Anodes in water heaters should be checked at least yearly and replaced when needed. Some water supplies could call for sooner replacement. If you replace them when they need to be replaced you'll never have to buy a new HW tank because of rust.Licensed Master Plumber / EPA 608 Universal License / 410a Safety Certified / Medical Gas Brazer/Installer
domwild Guru Joined: 16/12/2005 Location: AustraliaPosts: 873
Posted: 07:25am 01 Aug 2011
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My sacrificial anode looked like an aluminium rod which had a steel centre rod. Once the anode is used up, it is the steel centre rod which rusts and makes the water brown. Make sure the new one is not too long as putting one in with the ceiling in the way is no fun.Taxation as a means of achieving prosperity is like a man standing inside a bucket trying to lift himself up.
Notice. New forum software under development. It's going to miss a few functions and look a bit ugly for a while, but I'm working on it full time now as the old forum was too unstable. Couple days, all good. If you notice any issues, please contact me.
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