Accucraft Safety Valve 'O' Ring Size

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AEthelwulf

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My Accucraft Yeo has two small pop type safety valves that were leaking steam at all pressures. On taking them apart, the internal 'O' ring was found to be mushed and broken. Can anyone please tell me the correct size for replacements?
 
PhilP said:
M5 by one.

From the horses mouth..

PhilP.
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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.
 
AEthelwulf said:
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.
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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?
 
AEthelwulf said:
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.
Click to expand...
That was from the Accucraft repair agent I was standing next to at the time.

You can go to 4.5mm by one, which is a little easier to get the nut over, but a little bit harder to stretch into place.

PhilP.
 
PhilP said:
That was from the Accucraft repair agent I was standing next to at the time.

You can go to 4.5mm by one, which is a little easier to get the nut over, but a little bit harder to stretch into place.

PhilP.
Click to expand...
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?YeoSafetyValve.png
In my diagram, part A - the fibre washer is 5mm ID, part B - the valve body is 4.1mm ID, part E - the adjuster is 4.5mm at it's widest point.

What I need to know is the size of F - the 'O' ring. The ring in the picture is 2.5mm ID, 1.5mm CS (cross-section), and it does not fit inside the valve.

I am now wondering if I put the 'O' ring in the correct place, should it go underneath part C, or wrapped around the nut part of C, or threaded over the middle section of C?

Thanks again for everybody's responses.
 
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So if 5 mm X 1 mm is aout the OD and not the ID, then the ID is 3 mm, which looks correct.

1754226062053.png
 
"Phil, I was talking about the thread where the fibre washer is at (A). The O ring (F) is 1.5mm int dia x 1mm gauge. You can get away with a slightly stretched 1.15 int x 1mm O ring. I have them in stock."

Dave was talking about the fibre washer..

PhilP.
 
PhilP said:
"Phil, I was talking about the thread where the fibre washer is at (A). The O ring (F) is 1.5mm int dia x 1mm gauge. You can get away with a slightly stretched 1.15 int x 1mm O ring. I have them in stock."

Dave was talking about the fibre washer..

PhilP.
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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)?
 
AEthelwulf said:
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)?
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"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."

Again, a quote from my contact.

Hope this helps?
PhilP.
 
PhilP said:
"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."

Again, a quote from my contact.

Hope this helps?
PhilP.
Click to expand...
Phil, that's a big help, thanks very much. I will give it a go.
 
PhilP said:
"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."

Again, a quote from my contact.

Hope this helps?
PhilP.
Click to expand...
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.
 
Northsider said:
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.
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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.
 
I tried 3.0mm and 3.2mm nitrile balls in the bottom of the valves, neither seemed to help, steam was constantly lost from the valves. I have not tried stainless steel balls as mentioned above, I just go fed up of the loco not working, so I ordered a new pair of valves (part no. Z24) from Accucraft/Maidstone Engineering. After a bit of adjustment they are now blowing off at around 60psi, the loco now runs! It's just a shame the new valves are shorter and the extension tubes no longer push inside them.
 
Quit all that faffing about - give Dave Mees a call at Abbeybach Engineering Services - he'll likely stick a couple in the mail for you. I'll be seeing him tomorrow - I can ask if you like.
 
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