CIRCULATING PIPES, DAMPERS, &c. 21 



The great preparation necessary for cleaning and scaling a boiler, and the number of hands 

 required to attend with buckets, &c. to remove the crust, frequently prevent an engineer from 

 entering willingly on the task, unless he can calculate on sufficient time for the same ; it is 

 in proportion to the convenience afforded, that these duties may be expected to be fulfilled. 



FLUES need never be wider than to allow convenience for repair and sweeping, without 

 reference to the magnitude of the boiler, so that much gain may be obtained in heated 

 surface in large boilers by the introduction of an additional flue, when the breadth will 

 permit ; that is, the increased horizontal surface due to the dimension of a boiler for large 

 engines over that of smaller ones will, with nearly the same water-ways, afford sufficient space 

 for the flue as above, instead of increasing the width of the others to occupy the said space ; 

 thus the surface of two additional sides is gained for steam generation. Fifteen or sixteen 

 inches may be taken as a good standard for width ; it ought not to be much less, and need 

 not be much greater. 



30. As the safety of boilers must always be entrusted to the engineers, whose duty requires 

 them to blow off a part of the water therein contained every two hours, it has often occurred, 

 that from neglect, or from having their attention suddenly withdrawn from this momentous 

 operation, the water has been allowed to descend below the flues and fire-places ; this, though 

 rarely, might happen from a defect in the feeding-pump or some of its apparatus : the burning 

 of fire-places and flues is inevitable, and almost immediate, HO notice being given till the injury 

 is effected ; and much greater mischief might take place, under the circumstances, from 

 explosion even, when the water of the feeding-pump is violently repelled, and flashed 

 into steam of a high degree of expansibility, by the red-hot metal on which it is injected. 

 The above neglect, and its partial consequences, I have witnessed several times ; and it will 

 and must be expected to occur again unless some arrangement is made, in order that the 

 blow-off cocks or valves shall be closed, and the blowing off cease, when the water has 

 descended to a certain limit consistent with the safety of the flues. In fact, I have considered 

 blowing off, at all times, so important and dangerous an operation, that I never permitted 

 it to be performed without the attendance of one fireman at least, with the engineer of the 

 watch, whose undivided attention was directed to trying the gauges, till the moment prescribed 

 for shutting the cocks : so valuable a part of the machine as the boiler should not be left 

 entirely to the discretion of men who may or may not look properly after it. 



A "DETECTOR PIPE," as now fitted in some of Her Majesty's steam vessels, will effectually 

 give notice of the approach of danger, in case the water is allowed to become low, as well as in 

 cases where the action of the safety-valves becomes obstructed from any cause whatever, of 

 which we have lately had alarming instances. This pipe is bent like a syphon ; one leg of 

 which, two inches in diameter, to avoid becoming foul, descends beneath the water of the 

 boilers to a point above the flues, where they are perfectly safe. From the bend, the height 

 of which should be above that due to the pressure of steam in the boilers, a smaller leg 

 descends to the engine-room ; the bottom being directed towards the ash-holes, with stop- 

 cocks at hand, to be used when the boilers are entirely blown off" on arrival, and so arranged 

 that the cocks must always be open when the levers or spanners are removed. A hole is 

 made, or a tube inserted, in the upper part of the bend, so as to prevent the " detector" on 

 the inclination of the ship, or otherwise, from acting as a syphon. The steam rushing 



