Bye-Pass Valves

Bill Broadbent

When one has stepped beyond the platform ramp and entered the world of sleepers and ballast  , it is not long before one finds the tongues of the apparently taciturn toplink men begin to loosen, and it is then that a knowledge of shorthand would be invaluable to record the gems of reminiscence which all too often elude the memory thereafter. Now and again circumstances happily combine to prise such a memory from its dusty corner and it was so the other day as I watched 6221 swaying gracefully and proudly over Crewe North junction at the head of the down ‘Caledonian’, The symphony of movement of a well-proportioned, valve gear occupied my attention, as it never fails to do, and seeing the long-disused bye-pass valve castings on the underside of the cylinder the story behind this story emerged.

The Royal Scot class of locomotive is still well enough known today, but it is perhaps forgotten what great prestige was heaped on it during the early days of the ‘Royal Scot’ train. It may also have been forgotten that early examples of the class were fitted with bye-pass valves , which, if elucidation is necessary, were provided to reduce ‘pumping’ in the cylinders when coasting by allowing a passage of direct access between both ends of the cylinders. The action of opening the regulator caused the bye-pass valves to close and the normal power/exhaust resumed.

The snag with the bye-pass valve has always been its proneness to failure, and when failure occurs the cylinder concerned receives live steam at both ends for the period of admission pertaining, which results in some pretty useless looking indicator diagrams.

It was a grey afternoon in 1928 and my raconteur sat on the precarious perch provided by Bowen Cooke for drivers of his super-heated 4-4-0s. PTARMIGAN , not yet committed to the excursion siding at Llandudno Junction, stood alongside the horse dock on Crewe station pilot duties.

As he saw the loco arranger crossing the tracks towards him he looked at his watch and guessed half the situation when it told him that the up ‘Scot’ was ten minutes late. The remainder was soon revealed — 6104 was limping in with a middle cylinder bye-pass valve failure, and seven minutes later PTARMIGAN was running back on to the stationary train at Crewe North box home signal.

Train tare weight was 420 tons, quite a respectable load in itself, but, according to head office instructions, as 6104’s wheels would still circulate she must not be taken off the train, so, twenty-two minutes late, the Precursor shouldered her load of 550 tons and sent the sparks so high climbing Whitmore that they came down cold.

The run must have been stirring indeed: twenty-four late at Whitmore, twenty-two at Stafford, fifteen at Rugby and nine at Watford. With a slight check outside Euston the ‘Royal Scot’ drew in eight down.

What amazing feats of prowess those ‘Wessies’  could achieve. With these nostalgic thoughts of a colourful era I looked idly over to the horse dock, and saw a ‘Midland 2’ nosing up to the buffer stop — ah well, they don’t fit bye-pass valves nowadays.
(Taken from an old issue of the Festiniog Railway Magazine)