Re: SP 18 Question

That helps. Really that isn't pumping very much. Around the yard while the engine is running light the engineer is using the independent brakes which are straight air, this uses air directly from the reservoir to apply the brakes. The pump governor sees a drop in the pressure in the reservoir and sends steam to the pump to replenish it. This means you will hear the pump cycle frequently.

Now while the 18 is running with the train and stopping in Hermosa the number of pump cycles is actually normal. Again because the exhaust it a straight pipe mounted behind the stack it is clearly audible and in this case visible all the time. If it were plumbed into the smoke box like most locomotives you would barely hear it if at all. At Hermosa the engineer will use the automatic brakes to stop the train but once stopped he will apply the independent and release the automatic brakes, this will require the pump to cycle and refill the reservoir tanks. Small pump means it will cycle more times than later larger pumps.

RGS 20 also has one single stage air compressor it is larger but it has to to all the work and cycle quite often. However the exhaust is plumbed into the smoke box and it mostly unnoticeable by most, if you want some videos and listen carefully you can hear it cycling.

Larger locomotives like a K-36 have a two stage or compound air compressor, these pumps in these larger engines are not as audible, larger smoke box and shorter smoke stacks make it less audible.

Jeff Taylor
CRRM curator of equipment and rolling stock.