SteveW
Elder Statesman
Posts: 1,383
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Post by SteveW on Jul 25, 2004 12:53:48 GMT
A while back there was someone here complaining about an alledged poorly designed safety valve from a well known and reputable (should narrow it down a bit) kit supplier. The boiler had not been able to blow off enough steam to pass the boiler test and it was the supplier's fault.
We've had a couple of locomotives with the same problem at our club. All of them have sailed through the steam tests before but now don't. The only difference seems to be a batch of 'Magic Coal' bought as 'good stuff'. The trouble being it's too good for steam tests.
Suggested solutions to date have included adding more black gravel to the firebox during steam tests.
Currently the most effective cure has been opening out the vent holes on the screw-down bit of the safety valve. In one case it only took increasing the size of three of the six (alternate holes) to cruise through the test.
Could the root problem of failing steam tests be down to a general increase in the quality of coal rather than design of valves. Maybe the safety valve design needs evolving to cope with this improved coal. Maybe competition has weeded out the poor coal leaving only the very good stuff.
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Post by SpaceCadet on Jul 25, 2004 15:52:45 GMT
It would be interesting to calculate the area of the steam passage just below the ball and compare this to the sum of the areas of the vent holes in the screw adjuster. The latter should be equal or larger than the former.
Mr Gordon Smith of Burton on Trent Model Engineering Society wrote a excellent series of articles in Engineering in Minature on "Improving The Design of Safety Valves For Model Steam Locomotives" (February through March 2001). In The December 2003 edition of EIM, a Mr J. H. Oldland wrote about his experiances with Mr Smiths new design and highly recomended them.
The articles are well worth a read.
Regards /Ian
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Post by Phil Sutton on Jul 25, 2004 16:11:40 GMT
Gordon Smith is Boiler inspector at Burton MES,and is well respected for his research and production of safety valves.You won't go far wrong following one of his designs.
Phil
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Post by SpaceCadet on Jul 25, 2004 19:57:45 GMT
Phil,
Are you a member of Burton MES ? I have been trying to get in touch with Gordon Smith for a while because I beleave he sells the stainless steel springs required for his designs. I have sent him a few emails but without responce. Could you get a message to him ?
Regards /Ian
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