Unscrewing limescale-encrusted thread on a potable water system

[Caecilius]

Following on from an earlier post about a pressure reducing valve on a
megaflo cylinder, I've decided to remove the cartridge and clean out
the filter.

Guess what - it won't unscrew, and seems to be stuck fast with
limescale. Here's a pic:

http://i1021.photobucket.com/albums/af334/royhills/MegaFlo%20PRV/P1030654_zpsfa4e63e1.jpg

So the question is: what's the best way to tackle this? I assume
plus-gas and WD40 are not a good idea because this is connected to the
potable water supply. Would it be worth using some sort of descaling
cleaner to remove the limescale, or wouldn't that get down into the
threads?

I'm using a 12" adjustable spanner, so one option is to use a longer
one - like a big set of stilsons, but I'm worried about putting too
much stress on the surrounding pipework.

[The Medway Handyman]

Get a blow torch on it if possible, the expansion will crack the limescale.

--
Dave - The Medway Handyman www.medwayhandyman.co.uk

[stuart noble]

On 16/02/2013 15:03, Caecilius wrote:

Giving the spanner a sharp tap with a hammer is better than putting
pressure on it. It's the impact that shifts things

[Nick]

"The Medway Handyman" <davi...@blueyonder.co.uk> wrote in message
news:XnPTs.202999$T25....@fx13.fr7...

Would there be any plastic/rubber components within? Heat might damage
these.
What about cleaning thoroughly with wire brush, and a few taps around the
periphery with a toffee hammer. Then a few drops of Plus-Gas or similar at
the joint, leave to soak and repeat as seems fit. I can't imagine WD40
having much effect. A few drops isn't going to greatly contaminate the
system. Then a well fitting ring spanner and give it a decent thump whilst
bracing adjoing pipework.
If all else fails, and I hesitate to say
this...........................................................angle
grinder.
Nick.

[Caecilius]

On Sat, 16 Feb 2013 18:13:33 -0000, "Nick"
<nick...@NOSPAM.tiscali.co.uk> wrote:
>Would there be any plastic/rubber components within? Heat might damage
>these.

Yes, I suspect there may be heat sensitive stuff inside, so I'm wary
of using a blowtorch.

>What about cleaning thoroughly with wire brush, and a few taps around the
>periphery with a toffee hammer. Then a few drops of Plus-Gas or similar at
>the joint, leave to soak and repeat as seems fit. I can't imagine WD40
>having much effect. A few drops isn't going to greatly contaminate the
>system.

> Then a well fitting ring spanner and give it a decent thump whilst
>bracing adjoing pipework.

I wish I could use a proper spanner, but it's about 40mm (or one and a
half inches) across the flats, so I don't have a spanner that would
fit. And most spanners only seem to go up to about one inch anyway. So
I need to use an adjustable, which is not the best thing for these
circumstances.

>If all else fails, and I hesitate to say
>this...........................................................angle
>grinder.

No, stilsons come before angle grinder surely.

[Tim+]

Can you soak a rag in descaler (vinegar maybe) and drape it over the valve?
Maybe wrap it in cling film to stop it drying out.

Tim

[stuart noble]

Do acids dry out? IIRC the stronger ones at least get wetter when
exposed to the air

[Caecilius]

On Sun, 17 Feb 2013 08:02:42 +0000, Tim+
<timdow...@nospampleaseyahoo.co.uk> wrote:
>Can you soak a rag in descaler (vinegar maybe) and drape it over the valve?
>Maybe wrap it in cling film to stop it drying out.

The pipes are copper, and the valve body is brass. So I don't think
vinegar would be a good idea, as it tends to corrode it.

I'm sure I can remove the surface scale easily enough, but I think
it's the stuff in the threads that's causing the problem. So I'd need
something that would wick down the threads and dissolve the limescale
without corroding the metal.