So my solar cylinder has failed :(

Mothman

and I need a new cylinder.

My solar system was installed in 1998 with a 300l dual coil glass lined cylinder.

The upper coil seems to have corroded. The magnesium diode was never replaced. This magnesium diode was probably explained to me at the time but the significance of it probably never registered.

I would like to replace with similar spec. That is 300l dual coil with immersion in the middle. No good having immersion near bottom and leaving nothing for the solar to work on.

the height of my current cylinder is 1450mm but the space could accommodate 1800mm height.

Is stainless steel the way to go?

Would make getting upstairs easier as the glass lined are a brute weight.

I would like something to last a lot longer than 13 years. I reckon any money savings gained are being wiped out by this replacement cost:(

I would like recommendations of suppliers please
By pm as per forum charter

therightangle

I dont mean to deviate your thread but was it a limescale problem?

Just wondering does this happen more often in hard water areas?

Mothman

Softwater & mains.

I've found the plumbing section here on boards so have been looking through it.

Issues with stainless steel seem to be mainly with well water. Don't fancy going with glass lined again.

A lot of 300l cylinders seem to be 2000mm or more in height. I don't have this space, so the options are reduced.

quentingargan

Thirteen years without changing the anode is pretty good going. And quite a few installers never told anyone about the anode.

I have seen stainless steel cylinders failing in West Cork for some reason, but seldom elsewhere. Our own water here has a very low ph, so that might be part of the reason, but I don't think it can be the only one. I've been a bit baffled about this phenoneman and if anyone has clues, I'd like to hear of them.

Q

saibhne

Hi Mothman - PM sent.

Thanks,

S.

quentingargan

therightangle wrote: »

I dont mean to deviate your thread but was it a limescale problem?

Just wondering does this happen more often in hard water areas?

No - this is a separate issue. Glass lined cylinders have normal steel, which can easily corrode, protected by a thin enamel layer. Should any part of this layer crack, zinc from an anode migrates to coat the area of steel that has been exposed. Hence the term "sacrificial anode".

The zinc anode should be checked every year to see if it is being used up, and it should be replaced when it is getting worn away.

ccsolar

quentingargan wrote: »

therightangle wrote: »

I dont mean to deviate your thread but was it a limescale problem?

Just wondering does this happen more often in hard water areas?

No - this is a separate issue. Glass lined cylinders have normal steel, which can easily corrode, protected by a thin enamel layer. Should any part of this layer crack, zinc from an anode migrates to coat the area of steel that has been exposed. Hence the term "sacrificial anode".

The zinc anode should be checked every year to see if it is being used up, and it should be replaced when it is getting worn away.

Pm sent
Cc

Mothman

I still haven't decided on a replacement.
My 2nd coil needs to be a solid fuel coil, which on many cylinders is only provided in a triple coil cylinder.
One of the main issues for me is what I consider the paltry levels of insulation. The amount provided by most Irish and UK cylinders is 40-50mm. I'm looking for double this. My current cylinder has 75mm, my freezer has 80mm...even my fridge has 40mm!

After all an extra kWh lost per day mounts up over the life of the cylinder, even allowing for half the year when it is contributing to space heat.

quentingargan

Mothman wrote: »

One of the main issues for me is what I consider the paltry levels of insulation. The amount provided by most Irish and UK cylinders is 40-50mm. I'm looking for double this. My current cylinder has 75mm, my freezer has 80mm...even my fridge has 40mm!
.

The problem is that most cylinders are made for retrofitting in existing hotpresses, and even increasing the diameter by a further 100mm can plunge the vocabulary of most plumbers into depths they didn't know existed!

I don't have the figures to hand in W/M2K, but manufacturers claim that modern foams perform better, and that most heat loss is through poorly insulated fittings at the side of the cylinder.

According to the attached drawing from a text book for solar installers, if you have 5 side fittings, and three dome fittings, in a cylinder at 60C, you will be losing about 180W to 250W through these, or 4.3KwHrs to 6kwHrs per day. Attention to detail here may pay dividends. I like to use short lenghts of 1.5" armaflex over the pipe insulation and fittings, butted up to the cylinder, but some people use insulated tapes.

CJhaughey

quentingargan wrote: »

Should any part of this layer crack, zinc from an anode migrates to coat the area of steel that has been exposed. Hence the term "sacrificial anode".

This is not how a sacrificial anode works, the anode is lower on the periodic table than the steel the tank is made from.
Instead of the steel rusting (iron oxide) the anode corrodes (goes into solution) as it is made from a metal that is lower on the galvanic table. (more active).
Magnesium is the lowest on the galvanic table Aluminium and Zinc are above it so Mg will dissolve long before Al or Zinc in a freshwater system.

quentingargan

CJhaughey wrote: »

This is not how a sacrificial anode works, the anode is lower on the periodic table than the steel the tank is made from.
Instead of the steel rusting (iron oxide) the anode corrodes (goes into solution) as it is made from a metal that is lower on the galvanic table. (more active).
Magnesium is the lowest on the galvanic table Aluminium and Zinc are above it so Mg will dissolve long before Al or Zinc in a freshwater system.

Thanks for that CJH. I had read that before somewhere and forgotten it. Am I right in thinking that the anode will sacrifice more rapidly if there is damage somewhere to the cylinder - e.g. if you over-tighten a fitting and cause a hairline crack in the glass? Or does it just degrade at a rate that depends on other influences?

Not that we see many of these cylinders. Too heavy for most plumbers to bring upstairs:)

CJhaughey

Quentin
The rate an anode degrades at is proportional to the amount of metal it is protecting, thats why boats typically have a few along the hull.
If the fittings are overtightened and the enamel cracks bare mild steel is exposed.
This is what the anode sacrifices itself to protect.
If there is lots of mild steel then the anode will degrade faster.
I have a 400litre one of these tanks on the ground floor heavy indeed!
Stainless is good but not just a simple solution, there is active and passive stainless and if subjected to conditions of low O2 then passive stainless can start to corrode due to an inability to regenerate the protective layer on the surface.I wonder if well water sometimes has low o2 and therefore may accelerate corrosion?
The choice of material is critical to a long lasting product and the welding will be an important part of that.

freddyuk

I have a stainless steel pressurised cylinder (but installed vented) which is a direct feed to my WBS so there is no new oxygenated water being introduced. Do you think this is safe from corrosion as it is well water originally but not being replenished. I am slightly worried as I removed the anode to use the inlet port (just the right size and position) but I can use some inhibitor as it is not potable water. Trouble is inhibitor can damage seals in the pump so I have not used yet.
Any opinions are appreciated.

Coles

Are there any genuine technical reasons why copper cylinders mightn't be suitable for a solar collector system? Why are Stainless Steel cylinders usually installed?

quentingargan

Coles wrote: »

Are there any genuine technical reasons why copper cylinders mightn't be suitable for a solar collector system? Why are Stainless Steel cylinders usually installed?

Until recently, copper cylinders were cheaper than stainless, so were more common. Generally stainless lasts longer in areas with acid water, and it is easier to make a stainless cylinder that withstands high pressure, so if you wanted an unvented (or pressurised) cylinder, you usually opted for stainless in the past.

These days, the prices are closer together so the emphasis has changed.

Coles

quentingargan wrote: »

Until recently, copper cylinders were cheaper than stainless, so were more common. Generally stainless lasts longer in areas with acid water, and it is easier to make a stainless cylinder that withstands high pressure, so if you wanted an unvented (or pressurised) cylinder, you usually opted for stainless in the past.

These days, the prices are closer together so the emphasis has changed.

Unvented central heating systems are rare enough in older houses except where the attic has been converted, so there isn't really any need for the higher grade cylinder in most cases. But, I suppose if the cylinder has to be replaced for the extra coil then it may as well be a SS one. The prices are outrageous though...