a represents anin the upper part of a boiler ; over this aperture it fitted a short turned rned true at the top with a round edge, so that a steel plate c, flat and smooth on its under side, may touch at every part ; this steel Plate is suspended by a joint, to a curved lever d, whose fulcrum is at e, and which is loaded at the other end with a weight of 10 pounds. Now, as the lever has a power of five, (as shown by the five equal dotted spaces,) the plate c is pressed down upon the edge of b, with a force of 50 pounds; but when the lever and %eve/at am raised. by the pressure of the steam, into the position 4h %sin by -he dots. the force acting against the steam is reduced to 40 pounds ; and, in proportion to the force of the rush of the steam, by which the lever would be raised higher and higher, would the resistance be reduced to 30, 20, &c. as marked. This valve might be enclosed as usual, in a box, with a pips to conduct off the waste steam.
The subjoined diagram is explanatory of another mode of producing a similar result, but by different means ; a is the aperture in the boiler, on which is fixed a gun-metal plate or valve seat; b is a steel cup-valve, turned rounding at the edges, resting on the seat, and suspended to a straight lever c, whose fulcrum is at d. At e, is the weight suspended to the axle of a little wheel, which is made to traverse freely the upper side of the lever c, but whereon its range may be limited by means of a eliding stop f, provided with a set screw. g is the valve box, and h a pipe to carry off the waste steam. It will now be obvious that when the steam lifta the valve, the load on the lever will move towards the fulcrum to any extent desired, and thus the boiler may be relieved in proportion to the exigency of the case. It scarcely need be remarked, that our reason for making the valves with edges pressing upon flat surfaces, was to prevent tLe possibility of their sticking in their seats ; which, with the conical plug-valves is a common occurrence, and one that has been productive of serious accidents.
The safety-valves employed by Woolf, are calculated to prevent to then. seats, and are of great simplicity ; their form is represented in the margin, Fig. 1 being a plan, and Ay. 2 a vertical section. The shape may be consi dered at first in a solid cylinder with a circular plate at top; three large longi tudinal grooves, as shown at a a a, reduce theesdinder to the figure represented. The plug thus made, fits ttasily into the aperture of the boiler, and the steam which fills the grooves, pressing against the under surface of the head, raises the plug and escapes. The plug is loaded either by a weight, suspended to it inside the boiler, by weights laid directly upon the top, or by the agency of a loaded lever.
In a letter to the editor of the Leeds Mercury, Mr. Benja min Hicks, of the steam-engine manufactory at Bolton, in Lancashire, says, " I am induced, in order to prevent the accidents occasioned by the bursting of steam-boilers, which are of such frequent occurrence, and generally so dreadful in their consequences, to send to you the drawing and descrip tion of a self-acting safety-valve, of my invention, (or rather application to a new purpose; a similar valve having been used as a clack for a pump, upwards of a hundred years ago.) You will readily perceive, from the several advantages it possesses. that wherever its adoption shall take place, it would scarcely be possible for an acci dent of this nature to arise.
" The opening in the lower part of the box, which is fixed on the boiler-top, or, if more convenient, on any of a pipe having a free communication with it, requires to be of such a size, as to allow a free discharge of all the steam the boiler is capable of generating. This opening is covered with a spherical valve, (the outer part of which is brass, filled with lead,) of such a size, and conse quently weight, as to press with as many pounds per square inch, as it is intended the strength of the steam, at a svaataturn, in the boiler, shauld ever be raised to; the obvious effect of which will be (owing to its being perfectly free from friction,) that, at the very instant the steam arrives at that degree of pres sure, the ball will be raised, and a discharge instantly take place. The pro jections are merely to prevent the ball at any time from falling off its seat.
"From the nature of its construction, requiring no packing or attention, it can be entirely secured from the interference of careless attendants, and a pipe may be attached to the branch of the box, and continued into the chimney, or any other convenient place of discharge. I should not recommend this valve to be used as a substitute for the ordinary eafety-valve, (improperly so called,) but in all cases in addition, and so loaded, as only to be brought into action at a very trifling additional pressure above that, to which the other valve is weighted. This valve would be found of the greatest advantage, in preventing the boiling over of the feed-pipes of boilers, when the rooms over them are used as drying stoves print-works, bleach "I ought to state that f have had this description of valve in use for upwards of four years, with the greatest regularity of action." Another valve, of a very peculiar description, and especially adapted to afford security against explosion in largo boilers, was invented by Mr. Soot!, of Lam beth, who received an honorary reward from the Society of Arts, for the com munication of the invention. It is represented in the subjoined cut.