On looking at your response again, don't think this can be correct, the inside of the safety valve is less than 5mm diameter, so 5mm + 1mm + 1mm would be 7mm total which would be too big. I think the 'M5 by one' refers to the fibre washer used for screwing the safety valve into the boiler. The black rubber (?) 'O' ring that goes inside the safety valve beneath the spring must have a total diameter of no more that about 4.5mm.
I would either try to get a few different sizes around your thoughts or ask Roundhouse to supply some as I reckon that there will be little difference in size between their and Accy valves. You could also try to contact the UK Accy crowd?
That was from the Accucraft repair agent I was standing next to at the time.
Phil, thanks very much for your response, but 4.5mm would be far too big. I have just remeasured the internal diameter of the valve body, it is 4.1mm. Could it be that the Accucraft agent was talking about the standard size safety valves as fitted to Ragleth etc?
Phil, excellent thanks very much I shall try 1.5 x 1.0. But where do I fit it? Loose at the bottom of the valve body, or on the centre piece (C on my diagram)?
Thanks Jimmy
"F needs to go under C. Normally an M3 S/s ball in these though the modern ones may have an O ring. Not taken one of the new ones to bits yet as I haven't needed to."
Phil, that's a big help, thanks very much. I will give it a go.
I don't want to muddy the waters, but my Accucraft Peveril had a Ø3mm nitrile ball, not stainless steel. S/S probably better, as the original nitrile one got squashed over time, although it's replacement has been fine.
Yes, well muddied! I had best look into 3mm stainless steel and nitrile balls too, that does seem more sensible than a loose 'O' ring in in the bottom of the valve.
