Cylinder Drain Cocks, always faced forward on BR loco's, however in the USA they faced outwards! Used for clearing water/condensation in the cylinders on steam loco's. Water in a cyclinder as you will be aware will not compress and hence bent con rods or blown out cylinder casing ends can result so hence the drain cocks fitted. Also they can be used at any speed in addition to cold starts or lengthy station stops, example would be when water in the boiler was allowed to "get out of site" or in the top nut as we called it in BR days, water could carry over via the regulator valve in the dome via the steam pipe which feeds the cylinders with steam, if a loco is fitted with super heater elements water can enter from the steam header in the smokebox (front end) and continue to expand with steam. The outcome of this could be difficulty or non ability to stop the loco from moving even when it is screwed down with the brake, can also result in bent rods etc! A good driver and his mate up front would have the job in hand and never get into that state! Cylinder drain cocks are usually closed as soon as possible after moving off but there is no one answer as it is all dictated by loco conditions, boiler water level, wheel slip and water carry over risk, salts in the water which produce foaming effect or a loco overdue a boiler washout etc, one particular loco BR STD Class 8 71000 Duke of Gloucester had its cylinders lubricated by atomised steam via the drain cocks so the lever to shut off the drain cock steam needed particular accuracy in order to reduce wear to the inside of the cylinder piston rings. Also operation of the drain cocks should be used occasionally when being dragged in light steam, this reduces back pressure within the system. Sorry for lengthy reply but it cant be answered in a one liner but a simple but complex operation by a skilled footplate team deserved a complex answer. Happy days I remember them well!!!!
