Here is a test fit of the two safety valves. The valves are mounted above the main steam lines out of the boilers. Each valve is intended to limit steam pressure in the boilers at 40 psi, maximum. The 6-inch blowoff pipe running between the two valves is to be connected to an exhaust line
The lead cubes weighting the valves are putting about 210 lbs of downforce on each lever. Each seated valve, assuming a 40 psi boiler pressure, produces an upward effort on the lever arm of 784 lbs. The length of the lever arm, measured from the fulcrum to the weight, is 15.86 inches. A 15.5 inch value is reported in Peterkin as the distance from the valve center to the weight, but re-calculation of the lever's properties suggests about 15.5 inches is actually the full length of the lever arm. This is a good thing because a longer lever would not easily fit in the tight available space.
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test fit s-valves.jpg [ 84.76 KiB | Viewed 3697 times ]
Here is one of the two valves seen from below:
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s-valve from below.jpg [ 80.26 KiB | Viewed 3697 times ]
The position of the weight, straight aft of the valve, is conjectural, but it is the only way it can be made to fit in the available space without rotating it off-axis. Note that in an emergency, if you needed extra horsepower, you could probably tie down the safety valves with a loop of cable over the lever arm and under the steam output pipe. Here is the mechanism with the outer castings turned off:
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safety valve mechanism.jpg [ 32.66 KiB | Viewed 3694 times ]
The part of the valve exposed to steam is 5 inches in diameter.
Seen from below the valve seat casting looks like this:
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valve seat from below.jpg [ 35.37 KiB | Viewed 3694 times ]
The valve bodies and pipes are based on a beautiful formally drafted, fully dimensioned drawing in the Stevens collection. The weight and its hanger were done from formal drawings reproduced in Peterkin. The rocker arm and its linkage, however, are CADed from a doodle, hand drawn in pencil on the formal drawing of the valves. It is an ancient doodle, possibly done in a hurry by Ericsson or McCord. The centers and dimensions can be relied upon, but the style or 19th century "look" of this external mechanism is just a guess on my part. For examples of contemporary safety valves I used photos of English Great Western locomotives from the 1850s-60s.
The safety valves protrude up between the deck beams, and a concern was whether or not the weights would clear the forward face of the aft deck beam. It worked out okay, as shown here.
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clearance between beams.jpg [ 51.98 KiB | Viewed 3678 times ]
Immediately aft of the safety valve for each boiler is a main steam valve, in draft form in here:
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Main steam + Safety valves.jpg [ 53.21 KiB | Viewed 3648 times ]
Michael