32: penberthy

This update focuses on the Penberthy appliances: the injector and the boiler sight glass (sometimes shorthanded as “waterglass”).

The injector is a fairly important part of the locomotive. It allows the crew to add water to the boiler. Now, since the water in the boiler is pressurized (125 psi, or 8.5 atm gage), and the water in the tender is at a cool 1 atm, it requires work to put 1 atm water from the tender to the 8.5 atm boiler. In the 1800’s, the crew used to have a hand pump, and that gets tiresome quickly. The period that the CK Holliday represents had a crosshead driven pump, but that only works when the crosshead is in motion–that is, when the engine is moving.

So, the injector was invented to literally inject the water into the pressurized boiler. It works by combining steam and water in a chamber, and shoots this water/steam mixture out of its outlet. This is a very simplified explanation, and of course there is a lot going on inside this “mixing” chamber.

Here’s how the injector is laid out on the CK Holliday.

The above is the right-hand injector (engineer’s side). There are two injectors, one on each side (not shown). Generally, only the fireman operates the injector (left side), so the plumbing you see above will mostly go unused!

The water supply comes from the tender. It’s plumbed under the running board and up into the injector. The boiler feed water pipe also runs similarly under the running board, which goes to a check valve so that the boiler’s internal pressure does not release its water out the feed pipe. The injector overcomes the boiler’s internal pressure by about 50 psi. Update: Steve D at Burnsland corrected me. The overcoming pressure from the injector is actually about 8 psi.

The water sight glass, also by Penberthy, is a simple device that allows the crew to visually monitor the boiler’s water level. Its plumbing is made to simply allow the water in the boiler to rise up the waterglass. Reading the glass takes some experience, as the water will not necessarily read to its true level while the engine is in motion.

Plumbing is quite a tedious process!

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