With the throttle closed, steam was still entering the three cylinders making for some anxious moments as the engineer moved the engine about. This mystery steam wasn't a problem if the "johnson bar" was in "neutral."
Speculation was that one or both gaskets at the base of the throttle body, where it meets the dry pipe, went bad. This would allow steam to freely enter the dry pipe irregardless of the throttle setting.
In early November, several shop volunteers removed the steam dome cover and inspected the joint where the two gaskets are located. With the boiler cold and with the "beyond the spool valve" side pressurized, no leaks could be found.
In preparation for hydro testing the boiler a few days before the first North Pole Express train (4 Dec 2009) other shop volunteers filled the boiler to begin the hydro test. Not surprisingly, the steam dome cover leaked. It is not uncommon for the copper gasket between the boiler's steam dome and its lid to not seat properly and for leaks to develop.
The typical remedy is to either anneal the copper gasket or manufacture a new gasket -- depending on the condition of the original gasket. In this case, the gasket had been reused several times and it was severely gouged forcing the building of a new gasket.
Here, Dick D. and Dan H. inspect the lid to the steam dome. Besides the gasket being worn out, there was a good amount of crust embedded within the mating surfaces.
The gasket is made from 1/4" diameter copper rod, formed in a circle, and brazed at the joint. The freshly manufactured copper gasket is annealed by heating it until it glows a dull red and then quenched in a bath of cold water. While this practice will harden steel, it will soften copper.
A view of the steam dome. Part of the hydro testing is heating the water to about boiling. The steam seen rising from the dome is a result.
The gasket ended up being destroyed in the annealing process (a bit too much heat was applied to one spot and the copper started to melt).
As the staff was pondering the fate of the gasket (and new copper gasket material was making its way from Des Moines), it was decided to replace the two throttle body/dry pipe gaskets despite having "no trouble found" in the earlier diagnostics. A good portion of the labor to remove the throttle body was already spent (that is, the removal of the steam dome lid) so the additional time to replace the gaskets was considered preventative maintenance.
This picture is looking down into the steam dome after the throttle body was removed.
The throttle body suspended from the overhead crane.
Shop volunteer Dallas K. operates the overhead crane to move the throttle body to the work bench.
Dallas steps inside the steam dome to clean the gasket surface on the dry pipe. Some other bits of debris had fallen inside the boiler, so while Dallas was inside the boiler, the flotsam was removed.
MCRR President Matt C. cleans some excess material off the gasket.
Experience has shown that one of the two gaskets needs to be softened before installation. The gasket seat is tapered and cold, flat gaskets don't quite make it in that environment.
The throttle body being hoisted back to its home in the boiler.
Shop supervisor Mike E and Dallas K discuss the replacement of the throttle body.
The new gaskets were fabricated and installed by about 12.30 AM that evening.
There was one concern: the gasket needing softening due to being placed in the tapered joint was made with the "thinner" gasket material. Typically the "thicker" material is used, but none could be located.
After discussing this dilemma with our Des Moines courier, Griffin W., he poked around the shop and located the correct material. Rather than stay up any later, the first task in the morning was to make a new gasket, remove the throttle body, swap the thinner gasket for the thicker gasket, and replace the throttle body.
Here, Griffin W cuts the new, thicker gasket.
After reassembling the throttle, Griffin W and his colleagues completed the job by fitting the new gasket to the boiler, replacing the last few studs on the steam dome that were destroyed during the steam dome lid removal.
While the steam dome work was in progress, Dustin B cleaned and replaced the valve packing for the fireman's side sight glass. Something had plugged the lower entryway making the sight glass unreliable.
Dustin D, Griffin W, and Abe C "yuk it up" during the last few minutes of the repair job.