I have a Myson fan assisted radiator with 3/4" female brass connections to the heat exchanger. Would it be better to use 3/4" taper fittings with PTFE or Loctite stuff or 3/4" parallel ones with a fibre washer? The taper ones make better sense to me, but is there any risk of splitting the connections if they are as cheap and nasty as most things are these days?
(By the way, I am seeing 19mm brass threads in the catalogues now - are they some evil EU standard instead of BSP?)
Are the Myson fittings terminated with a machined flange, or are they as forged (not likely)? The presence of a flange implies they should be fitted with parallel fittings and a fibre washer.
Female taper fittings are shown on this page
Thanks for the answer, but I'm not totally sure I understand it. The fittings on the radiator are female, and have no obvious face on them, although they are fairly flat. In fact, the flats of the hexagon are within about 1.5mm of the root of the thread, so I doubt a washer would seal well. I presumably want a male 3/4" fitting, and I am leaning towards a taper thread one.
OK if there is no obvious face, then they almost certainly need a taper fitting. I'm never really happy with PTFE on these, I always use the Loctite "string" (which replaced the traditional hemp plus boss white). No other sealant required.
I had a Myson under-unit fan assisted rad years ago but I'm not quite sure what fittings they had. I "suspect" they had flexible hoses with push fit at the "copper" end, and male tapers at the "radiator" end.
I am slightly surprised they don't have instructions specifying the requirements. These days you can usually find the "manual" on the web.
What makes you think they are 3/4" BSP? If they measure around 20mm, chances are that they are 1/2" BSP.
[With BSP the size relates to the nominal bore of an iron pipe with a thread on the outside - so if the bore is 1/2", the thread is bigger than that, and is actually a bit more than 3/4"]See
The instructions say that they have femal 3/4" fittings and a straight fitting is preferred (to an elbow presumably, but this is not stated) to facilitate the routing of the pipes. Nothing about whether the fitting should be a taper thread. I agree about the Loctite, by the way, it seems to be very successful. I might have used hemp on 3/4" years ago, it's about on the borderline. I think PTFE tape works ok on 1/2".
What is this 19mm thread, do you know?
The fact that they are considerably bigger than 1/2" BSP (combined with the rarity of 5/8" BSP) and that the fitting instructions for the equipment state that they are 3/4" BSP combine to convince me. To the extent I haven't bothered to measure them! The way the thing is packed (and I have to send it back as it is broken) make it somewhat difficult to measure anyway.
By the way, this is what I mean by 19mm:
It looks like 3/4" BSP, but that would be about 25mm, and not a standard metric thread. Is this just some misconceived naming, or do they translate the names of BSP threads when they use them on the Continent?
I think it's Screwfix who employ the rogue translater: Pegler themselves seem to describe the PX46 as "elbow, copper x female iron", and one of them is 22mm x 3/4". No mention of female iron in mm dimensions.
That's reassuring. I thought I was unaware of something important. No-one seen the same thing elsewhere?
No, it's a strange way of representing it. 19mm is pretty close to 3/4", so this is almost certainly referring to the nominal bore rather than to the thread. If you scroll down the SF page which you cite, you'll see that it specifies the thread size as 3/4" - which I take to mean 3/4" BSP.
If your rad has brass female fittings, then you probably don't want to screw a tapered male into it because you may just crack the female fitting. Therefore locktite, fernox lsx or a fibre washer is the only solution.
That was my concern! Thanks for the comment. I don't think the Loctite thready stuff is recommended other than for tight taper threads, and I have found it does need to be tight. There is no convincing seat for a fibre washer on the female fitting. How would the Fernox LSX be used, a parallet thread or not very tight taper thread? And does it need any inert filler like hemp or similar? Does it need any particular physical or chemical thread preparation?
Thanks in advance,
Can I beg for further advice/opinion? Is there actually any way of reliably making a leakproof joint between parallel threads in the absence of any provision for a washer or 'o' ring?
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