Oil gauge on Backhead?

On Plate 31 of the Martin Evans "Manual of Model Steam Locomotive Construction" it shows a picture of a partially assembled BR Standard 7 Britannia boiler (3.5 inch) with many fittings installed. One of these is a gauge right in the centre at the top of the backhead between twin water glasses, and although its a Bourdon tube style gauge it has just two sectors marked up, "NO OIL" and "OIL".

I assume its linked somehow to the reservoir on the lubricator tank but I've never seen one fitted to a scale locomotive before. Can anyone shed any light on it please?

Maybe the builder connected the oil pump output line to the gauge on its' way to the cylinders and other points oiled. That way the driver could see the status of oil pressure and from it, and infer the engine was getting oil.

Course you can also tell that from a) engine stays running b) stack has oily deposit in it c) clean white glove gets oily spots on it when placed over stack while running (where were those clean white gloves again?)

It is the late Roy Amesbury's 3.5"g Brit, and Roy described it in ME in 1966 or 1967. A search of the Index will provide the relevant MEs.

I cannot recall from memory whether Roy explained the 'oil - no oil' gauge, but he later described for his later GWR loco making all his own pressure gauges around 1972 and a duplex brake valve gauge. He later described his GWR President loco around 1982 with his homemade gauges. Roy worked at Rolls Royce in Derby.

Hope the above is some interest.

Cheers,

Julian