Pneumatic Points Plan B - Engine Taps

I love pneumatic point machines. They are simple, powerful and they make cool noises. Created in a time when electricity and electric motors were complicated and expensive, the technology has not aged well as the cost of labour has skyrocketed past the cost of technology. Case in point is the old conundrum of what what one does if the air all runs out. While electric point machines have the equivalent disadvantage of not being able to function without electricity, they have been able to make up for this limitation through the widespread adoption of the dual control point machine. Downed power lines got you down? No problem! Just throw that big old lever by hand and watch the switch points move.

You see the rotational gear train of an electric drive is able to mesh with the rotation of a hand throw lever. Pneumatic points on the other hand use a linear piston and crank system. While there are certainly ways to incorporate a hand control, it would probably require a major redesign and add a significant amount of complexity.

So what does one do if your pneumatic interlocking plant literally runs out of gas? Well a little hint can be found on old PRR interlocking sheets. At various points on the diagram there are notes indicating the presence of an "engine tap". Once common, this device seems to have been mostly eliminated at surviving pneumatic interlockings and it took me until 2018 to actually encounter one in the wild at the Brilliant Branch wye switch at CP-HOME.

An engine tap is a valve on the interlocking air line with a standard railroad air brake coupling on the other end. In case air pressure drops below minimum operating levels, perhaps due to a compressor failure or power loss, locomotives were expected to connect their own air supply to the engine tap and pump up the plant's air reservoir using the locomotive's own air system. In fact, while reading an old PRR book I remember a story about how during the Northeast blackout of 1965, the first engine movement authorized in the Philadelphia area was for a pair of diesel road freights to run lite to ZOO interlocking in order to connect to the air system and keep the interlocking plant operational.

Why were these useful devices removed? Well I have to assume that electric power and automatic air compressor became more reliable. There is also the risk of vandalism/sabotage if random people are able to simply vent an interlocking's air system to the atmosphere (recall that engine taps were usually included at manned interlockings with vigilant operators). Without the engine tap railroads reverted to a Plan C, which boiled down to having maintainers remove the cover, hand crank the points to the desired position (if necessary) and then spike and wedge the points until air power could be restored. Evidence of spike and wedge operation was in evidence at the Pensy high point CP-AR where each pneumatic point machine was provided with a brightly painted wooden wedge and matching railroad spikes.

 With pneumatic point machines rapidly vanishing it won't be long until the only place this sort of thing applies is Penn Station New York and Washington Union Terminal, and those places probably already have all sorts of more conventional redundancies.