Merlin Gas Valve

Fred2179G

Registered
20 Apr 2017
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Hi Guys,
I have an old Merlin Mayflower converted many years ago to vaguely american, using a wood cab and tender. I got it from an estate years ago.

20210709_114831-mayflower-tuck-inertia.jpg


It is a good runner, as the above photo will attest (Tuckahoe Steam & Gas Show, MD.) However, shortly after the pic was taken I had lunch and then set about preparing it for another run. I filled the lubricator and boiler, then the gas tank. Some time later I went to light the fire as it was almost my track time. I was early, so I turned the gas off after a few minutes so it would stay warm but not waste fuel.

Imagine my surprise when, all on its own, the safety valve lifted 5 minutes later. The gas obviously wasn't off! On investigation, it seemed I could turn it 'off' but there was still a residual flame and it didn't go out. Hmmm . .

This morning I cleaned the loco and took out the gas valve spindle. It seemed old and worn, so I gently polished the point with 400 emery. After putting it back together, I loaded a very small amount of gas and found I could light the fire without turning the gas on. My polishing might have helped but it didn't solve the problem.

Anyone seem this phenomenon before? Any suggestions for things that I can try?
 

Paul M

Registered
25 Oct 2016
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I've not known of it before, but it is probably not that unusual. Using wet and dry may make things worse if you scratch the surface. I'm sure you can buy replacement valves, try the Train Department
 

Fred2179G

Registered
20 Apr 2017
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I took it apart this morning so I could inspect the valve. The issue seemed to be that the valve stem is just brass, and therefore quite soft. It screws into a regular piece of ~1/16th pipe which is probably copper. A little black acrylic paint on the point showed me where it contacted the pipe/seal, although as I was turning it, it was impossible to see if the contact was uniform.

I lightly cleaned the pipe end (which is 3/4" inside the valve and therefore invisible,) with a fine round file and a 3/32nd drill in my fingers to clean off the end. Then I took the stem and chucked it in the hand drill and smoothed it again. I took the assembly (tank, valve, delivery pipe,) outside and put a small amount of butane in the tank. This time it seemed to seal. So I reassembled the gas feed and tried it with a lighter. It lit - but it also went out when I turned the gas off. Success.

I suspect a steel valve stem will provide a better seal, as it will force the pipe to fit around it.