The Locomotive Of Today

The Boiler : Test Cocks, Fusible Plugs. 47 is as follows:—When a glass breaks the sudden rush of water lifts the ball and carries it from its support to its seat, effectually stopping the flow of water; the steam similarly forces the top valve clown, and only escapes in a tiny stream through the small hole; it is, therefore, an easy and safe matter to approach, close the cocks, and fit in a new glass. This is done by removing the plug at the top of the upper fitting, and lifting out the valve. Stuffing boxes of an approved style are provided for the glass, as in the last example. In addition to the risk of scalding, tliat of being hurt or even blinded by the particles of glass exists, and protectors are now iitted to obviate this and save the glass from cold draughts and acci- dental blows. Wall’s patent, made by Messrs. Dewrance, consists of two or three pieces of plate glass fixted to end plates of gun metal, shaped to engage the glanel nuts so that it can be easily and quickly adjusted. This form of protector is shown on the column B, and also cletached at C. Hulburd’s protector entirely encloses the gauge glass and has a pipe connection to convey away all water and fragments of glass into the ashpan. In addition to the columns clescribed, the boiler should be provided with at least one test cock, by means of which the water level can be known, if the glass fails and becomes use- less. This test cock, or the lower one, if more than one are supplied, should be placed some four inches above the level of the crown plate so that clry steam issuing from it denotes that the water has reached its lowest limit consistent with safety. In cold countries, where glasses will not stand, three or even four of these test cocks are provided, and are arrangeel to dis- charge into a funnel with a pipe passing down below the foot plate. A simple form of cock is shown at D, in which the body screwed into the boiler plate contains a seating with a screw valve, having' a T handle and a mushroom collar just below it to intercept any steam that may escape past the thread. It was a universal custom to fit locomotive boilers with a fusible metal plug' in the crown plate, so that should the water level fail below the sheet the heat would melt the composition and allow steam to enter the firebox and extinguish the fire, but as these plugs were not always reliable many railways abandoned their use. E represents a simple form where an ordinary mud plug' is drilleri, throug'h, with the hole counter- sunk at the top and filled with a composition which melts when exposed to the heat without the protection of the water. This composition consists of an alloy of lead, tin, and bismuth. When employed these fusible plugs should not be allowed to run too long, as the metal is apt to become affeeted and will not then be reliable for the purpose intended.