The flow to my bath has dwindled over the years, it's a conventional vented cylinder and 3/4" copper pipes, is there likely to be any benefit in dosing the cold water tank with sulphamic acid and then recirculating through the bath tap connection with a pump?
AJH
A tub of fernox DS3 will make enough gallons to fill the tank and the cistern, so yup recirculating with a pump for a few hours should do the trick. Keep the immersion on for better performance (but don't let the cistern get too hot if its plastic - they can go droopy if not well supported)
Probably only a leak I'd say! Sounds a bit drastic to me. If the water is really that hard, maybe some way to make it less so might be a good idea. . How many years has it taken to be noticeable? Brian
Yes we all go droopy in the heat if not supported, what? I'm not convinced about this to be honest. I remember when we first moved in here and had flow issues in the bath my father trying this sort of thing. It did not work and it found a few pin hole leaks in the plumbing under the bath which in the end needed the pipes replacing and so we got a new bath and new pipes in the end. The question I always wondered about was how come the particular pipes were coated in scale inside but the very old but wider ones in the loft down to the bath and from the cylinder to under the floor did not though clearly they were older by some years.The plumber at the time said often life is like that, and shrugged. This was many many ears ago in the 1960s. Brian
My first house had a rivetted galvanised hot water tank, and many metres of iron pipe getting on for 2 inches OD in the gravity DHW system which must, once upon a time, have gone to a coal stove in the scullery. Some of this pipework was almost completely blocked with scale, there must have been kilogrammes of it in the whole system. My recollection is that while this particular type of scale dissolves readily enough in hydrochloric acid, the dissolution rate is quite slow in weak acids. So while I agree with the theory of your analysis, I'd worry how well it would work in practice. Heating should help.
Yup heating helps greatly...
The fernox instructions for a manual descale, suggest a minimum of 4 hours with the temp between 50 to 60 deg C.
You may get faster results with a continous recirculation system.
Thanks, to clarify I intend to first empty the galvanised steel cold water tank and wet vacuum any scale in the bottom. I was only going to part fill it and would add the fernox DS3 as you advise. I was then intending to attach a spare central heating pump to the 15mm shower connection which is TEEd off the bath hot water tap and return the water to the cold water tank via a length of HEP20 dumping back into the cold water tank.
AJH
Fernox DS3 is OK on glavanised, I take it?
Thomas Prufer
how do you plan to stop it attacking the copper pipe?
NT
It says it's safe to use but I don't know until an expert comes along.
My guess is the acid's affinity for the carbonate is higher than that for metal. it's moot about the zinc as that seems to have gone from the inside of the tank.
I hope if I use the right dose it will deal with the lime scale and leave the metals alone.
AJH
Most decsalers are weak enough acids to leave metals alone. HCl is not one of them. DAMHIKT
DS3 is not HCL, but sulfamic acid (H3NSO3), generally safe on metals, although may dull chrome on prolonged exposure.
Zinc gets eaten by pretty much everything, though.
I found a patent, including this language: "Even at room temperature Islamic acid rapidly attacks zinc galvanize; in aqueous solution at concentrations as low as 1.5% by weight, it is capable of completely dissolving a zinc galvanize coating from a ferrous metal base in two to three hours. Repeated use of Islamic acid even for short periods will severely corrode zinc galvanized equipment. The corrosive effect of the acid on zinc increases with temperature, and galvanize may be removed in less than 30 minutes at a temperature of 140 F."
And also this: "Weak acids such as citric acid, formic acid and sulphuric acid are suitable for use with metals such as aluminum, zinc, copper and nickel. Although these metals will be affected by these acids, this will be much less severe." A while back I asked a bunch of chemists with what to descale a pot with an intact, thick layer of zinc -- and didn't get a useful answer. I ended up using a wet stiff brush and elbow grease. This got rid of enough scale to be useful, say 80%, and was surprisingly efficient. The removed scale formed a milky soup that abraded the remaining scale very well...
In this case: if the zinc is gone, it won't be attacked. Just keep an eye on it, OK?
Thomas Prufer
WTF is Islamic acid?
Stuff you throw in peoples faces?
Interesting. IIRC the De Longhi coffee machine warns against sulphamic acid, there may be zinc plated screws in there. Lactic acid, apparently:
Do check there's not a thingie just inside the tap spout that's got furred up.
Yup good point - those aerator things are prone to scaling and getting blocked.
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