Valve Pilots

[Barry Ten]

Fascinating article in the current special edition of Classic Trains on the "Valve Pilot", which was a commercial product applied to selected big US steam power in the 20s and onward. I'd not encountered this equipment before and wondered if it ever had any application in the UK?

 

Basically it was a device connected to the rear driving wheel by a friction wheel, with a cam-driven mechanism which determined the theoretically most powerful cut-off setting for a given speed. The system was so effective that even experienced train crews were able to extract more effective horsepower from their locos than before, with the result that the tonnage rating of some locos was significantly increased. The device also produced a pencil-trace of cut-off versus speed, which enabled loco performance to be assessed over long periods of time. Rather than being hostile to the invention, crews turned out to welcome it as it helped them get the job down more easily, as well as exonerating them in cases of apparent slow running or where there was an accident and the locomotive speed was under suspicion. However, the article says the equipment really only became cost-effective in large locos where there was a proportionately worthwhile saving to be made in coal.

 

Anyway, it's a really good, detailed piece which touches on a bit of technology I'd never heard of before.

[dullsteamer]

I'm not aware of any application to a loco built for a UK railway, but I believe one was fitted as a trial to a Victorian Railways NBL-built R class 4-6-4.

[Hunslet]

I have not come across that device but the Pennsylvania Railroad used a friction wheel device on some of the Q2 "Duplex" locos to arrest the slipping between driver groups that occured with these locos.

This was the American Brake Shoe Co's "Slip Arrester" which was a differential switch driven by friction wheels on no. 2 and 3 drivers and would close a butterfly valve in the steam pipe of the slipping group.

I don't know of any UK uses of the "Valve Pilot" or similar devices.

Source, Profile Publications No.24.

[Barry Ten]

Another use for the Valve Pilot recording data was to monitor excessive wheel slip, and also incorrect use of sanding gear, which could put a massive strain on the valve gear.

[scots region]

More than that, it was able to record a cracked frame! Its a deep shame such a device was not used here, though, given that British locomotives covered far less mileage and over much easier terrain than their American cousins. A valve pilot may have have been useful for only a short amount of time.