Accucraft 3-cylinder Shay safety valve fail......................

tac foley

tac foley

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Well, Folks, I guess it had to happen sooner or later, the safety valve on my 3C-Shay, the very first example sold in UK, direct from the Accucraft stand to Steve Warrington and then me, has gone to the safety valve heaven. Checking the loco over for its annual documented test last Friday, after a three-month hiatus, and the SV failed to lift at the usual 65psi, and climbed to the stop, whereupon I turned it off and let it cool down.

Some suggest that the dome cover simply lifts, while others that it unscrews. Neither would seem to the case - without using what I consider to be undue force, that is. Given the rarity of these early versions, and its sentimental value to me, I'm loathe to apply too much by way of brute force.

Right now it's having another dose of penetrating oil in the only area where there just MIGHT be a thread...

The usual suspects have been contacted for advice - they know who they are, and thanks, Guys.

However, your suggestments would also be valued.

TIA
 
tac foley said:
Well, Folks, I guess it had to happen sooner or later, the safety valve on my 3C-Shay, the very first example sold in UK, direct from the Accucraft stand to Steve Warrington and then me, has gone to the safety valve heaven. Checking the loco over for its annual documented test last Friday, after a three-month hiatus, and the SV failed to lift at the usual 65psi, and climbed to the stop, whereupon I turned it off and let it cool down.

Some suggest that the dome cover simply lifts, while others that it unscrews. Neither would seem to the case - without using what I consider to be undue force, that is. Given the rarity of these early versions, and its sentimental value to me, I'm loathe to apply too much by way of brute force.

Right now it's having another dose of penetrating oil in the only area where there just MIGHT be a thread...

The usual suspects have been contacted for advice - they know who they are, and thanks, Guys.

However, your suggestments would also be valued.

TIA
Click to expand...
No helpful suggestions, just pleased you discovered the fault the easy way! :eek:
 
Neil, many moons ago I watched [from a safe distance] as a well-known maker's boiler was taken to over 700 psi before the test plug failed. Replacing it, it then went another 150 psi before letting go with a loud hiss, which quickly diminished to a low hiss. There is simply not enough volume in our little boilers to cause them to explode violently and the pressure reduces instantly the 'leak' starts.
 
I'm not sure what the arrangement is for the shay, but hears a pic of the ones fitted to the accucraft Isle of man Mona, you can see the hexagon outside of the valve to unscrew the whole thing, in the centre is the valve itself, the 2 slots either side of this can be used to adjust the pressure that it blows off at, screw this in to increase the pressure the it blows off, unscrew to reduce the pressure it blows off at (which is what you need) or to dismantle the valve, if you can or feel brave enough, I believe the best way is to soak the parts in vinegar to clean then reassemble.
Hope this helps.


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Thanks, the problem with the Shay is that the SV is housed in a dome that looks as though it should unscrew, but doesn't. No other visible form of attachment either...... :(

1645449234647.png
 
Is their a decorative safety valve on top of the dome, if their is try unscrewing that first and then the top section of the main dome, that's how I access the safety valve on my Accucraft loco.
 
DafyddElvy said:
Is their a decorative safety valve on top of the dome, if their is try unscrewing that first and then the top section of the main dome, that's how I access the safety valve on my Accucraft loco.
Click to expand...

Yup, the ornaments on the top are purely decorative. Right now they, and the steam pipe, are lying on the workbench beside the loco, which is having its third soak of penetrating oil.......
 
tac foley said:
Thanks, the problem with the Shay is that the SV is housed in a dome that looks as though it should unscrew, but doesn't. No other visible form of attachment either...... :(

View attachment 295510
Click to expand...
Just had a Google, I presume that it's in one of the 2 domes? Looking at the photo, towards the base of the dome at the front, is there a small hole, about 3mm? If so, there is probably a grub screw with an Allen key head?
 
Not that I know anything about this..

It wouldn't be a box spanner from above, would it?

Please feel free, to have a laugh at my expense. :blush:

PhilP
 
That looks very similar to my Lyn. I thought if you unscrewed the ornamental valve the top just unscrewed
 
Looking at the "gap" in the dome where it meets the "base", it almost looks like there is paint there? Could it be painted over and that needs to be "cut through" to remove the dome? Being perfectly round it would be a candidate to be threaded too, how did the decorations unscrew? Were they threaded into the dome "shell" or did one of them seem to reach inside to something else?

It sure looks like a candidate to unscrew. Now, my stupid question: how do you know there is something inside? (I said it was a dumb question)

Greg
 
I'm not laughing. There are four holes in the dome top section - three are at 120 degrees around it, and one, larger - about 3.5mm dia, in the middle. One hole is threaded and about 1.5mm, and is the location for the larger of the two dummy safety valves, and has a handwheel controlled valve set into a section of pipework. Another is just a hole, into which the whistle is located on a long spigot. the third is for the small safety valve, which is threaded and screws into the hole. The large hole in the centre is the aperture from which the steam escapes when the real safety valve, deeply hidden inside the dome, lets rip.

There are no visible screws, or setscrews of any description whose loosening would allow the dome to be removed.

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Greg Elmassian said:
Looking at the "gap" in the dome where it meets the "base", it almost looks like there is paint there? Could it be painted over and that needs to be "cut through" to remove the dome? Being perfectly round it would be a candidate to be threaded too, how did the decorations unscrew? Were they threaded into the dome "shell" or did one of them seem to reach inside to something else?

It sure looks like a candidate to unscrew. Now, my stupid question: how do you know there is something inside? (I said it was a dumb question)

Greg
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Greg, it's where the steam comes from when the safety valve lets go.
 
Greg Elmassian said:
Looking at the "gap" in the dome where it meets the "base", it almost looks like there is paint there? Could it be painted over and that needs to be "cut through" to remove the dome? Being perfectly round it would be a candidate to be threaded too, how did the decorations unscrew? Were they threaded into the dome "shell" or did one of them seem to reach inside to something else?

It sure looks like a candidate to unscrew. Now, my stupid question: how do you know there is something inside? (I said it was a dumb question)

Greg
Click to expand...
I am tempted to agree with Greg, on my Accucraft loco I unscrew the ornamental items on top of the dome and then unscrew the dome.

Could the model have received a coat of paint at any time and some has penetrated in the gap between the top and bottom of the dome gumming things up a wee bit?

My or other suggestion would be to put something over the dome to protect the paint finish and using a set of mole grips, not locked on to the dome, hold them on to a towel or similar and gently twist to unscrew, the amount of force obviously cant be put in words, but that's what I would try having seen the photo of the dome.

Maybe a silly question but what have Accucraft advised?
 
DafyddElvy said:
I am tempted to agree with Greg, on my Accucraft loco I unscrew the ornamental items on top of the dome and then unscrew the dome.

Could the model have received a coat of paint at any time and some has penetrated in the gap between the top and bottom of the dome gumming things up a wee bit?

My or other suggestion would be to put something over the dome to protect the paint finish and using a set of mole grips, not locked on to the dome, hold them on to a towel or similar and gently twist to unscrew, the amount of force obviously cant be put in words, but that's what I would try having seen the photo of the dome.

Maybe a silly question but what have Accucraft advised?
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As I explained earlier, all the brass pieces have been removed, thus exposing the holes I also mentioned. I have owned the model since it left the Accucraft stand at Stoneleigh in 2007. I have not repainted it except to colour the roof in red oxide to match all my other geared locos.

Because of the very tight constraints of the location of the dome, no mole grips would fit, so tomorrow I'm going to try and find a small strap wrench - that is usually made with a rubber or soft plastic gripping surface.

Accucraft here in UK has no dismantling-type knowledge of this mainly made-for-US model, but I have messaged Mr Cheng in the Accucraft San Diego HQ for any advice they might offer. I have not yet had a reply.
 
As David says, the dome's construction looks similar to that of Accucraft's Sea Lion: on that loco, the top section is threaded onto the SV housing, and closes onto the lower section of the dome, which is a brass pressing/spinning. If it is similar -and if I remember correctly- the penetrating oil will need to go just inside the aperture at the top of the dome cover. The joint where the paint is, is merely a butt joint, and is not threaded.
 
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