US2242798A - Boiler drop plug - Google Patents

Description

y 2 1941- R. N. MILLER 2,242,798

BOILER DROP PLUG Filed June 6, 1940 INVNTOR: Eaberi M BY W W A TTORNE YS.

Patented May 20, 1941 BOILER DROP PLUG Robert N. Miller, Rosemont, 'Pa., assignor to The Pennsylvania Railroad Company, Philadelphia, Pa., a corporation of Pennsylvania Application June 6, 1940, Serial No. 339,079

1 Claim.

This invention relates to safety plugs for steam boilers and, more particularly, to the type comprising a tubular body-member with a drop-plug normally sustained therein by a fusible bushing adapted, under a given temperature, to melt and release the drop-plug, whereby escaping steam will eiiect an audible Warning that the water in the boiler has lowered to an undesirable level.

The primary object of this invention is to provide an improved drop-plug of the indicated species including novel features whereby the emciency is greatly enhanced.

Another object is provision of a drop-plug of the type above referred to that is devoid of any creeping or sticking tendencies, which is simple to manufacture, easy to install, cheap in production, and withal is positive and reliable in action.

Other objects and ancillary advantages of this invention will appear as the nature thereof is better understood, said invention consisting substantially in the novel features of construction, combinations and arrangements of parts herein fully described and illustrated by the accompanying drawing; wherein similar reference characters are used to designate corresponding parts throughout the several views; and then finally pointed out and specifically defined in the concluding claim.

In the drawing:

Fig. 1 is a vertical section through one typical form of drop-plug constructed in accordance with this invention, and preferably adapted for application in locomotive boiler crown sheets, a fragmentary portion whereof is shown.

Fig. 2 is an underside plan view of the same.

Fig. 3 is a perspective View of a fusible-bushing included in the drop-plug structure.

Fig. 4 is a perspective view of the releasable component or drop-plug detached from the associated body-member.

Fig. 5 is a section similar to Fig. 1 of a slightly modified form of the invention.

Fig. 6 is an underside plan view of the preceding figure.

Fig. 7 is a central vertical section through a further typical form of the invention; and,

Fig. 8 is an underside plan view of the said figure.

In the following detailed disclosure of the embodiments of this invention shown by the accompanying sheet of drawings, specific terms will be employed for the sake of clarity, but it is to be understood that such terms are used in a descriptive sense and not for purposes of limitation.

Each specific term is intended to include all technical equivalents which serve in a similar manner to accomplish an analogous purpose.

In the practice of this invention, and referring descriptively to the embodiment thereof, shown more particularly by Figs. 1-4, inclusive, the body-member of the drop-plug is comprehensively designated by the numeral I, said member consisting preferably of a machined annular body portion including a taper-bored upper part 2 and an externally taper-threaded lower part 3, for screw engagement in a correspondingly-threaded aperture 5, provided for its reception in the crown-sheet 6.

Interiorly, the body-shell portion 3 is appropriately formed to define a polygonal-shaped socket l for insertion of a suitable key whereby the said member is threaded into or drawn-out of the crown-sheet aperture 5; and said socket has an adjoining annular groove 8, for preventing formation of burr during finishing of the socket, with a relatively smaller 'counterbore 9 communicating with the lower end of the plug main bore II]. This bore 10, it is to be particularly noted, is preferably outwardly divergent in form, substantially approximating to a threequarter inch taper in a longitudinal dimension of one-foot; and it is conveniently press-fitted with a scomplementally-tapered fusible-bushing ll. Into this bushing l I is press fitted the releasable closure or drop-plug 12, said plug having a taper conforming with that of the bore Ill, the major or upper end l3 having a diameter slightly less than the smaller diameter of said bore. Creeping of the plug l2 in service is thus eliminated by compression of the fusible-bushing ll, incidental to the press-fit application of said plug; while sticking is eiiectively prevented when the plug I2 is released for blowing out. In addition, the drop-plug I2 may be provided in its smaller end M with an axial recess l5 for purposes of proper centerin of said plug, relative to the bore Ill, when such plug is initially secured in position either by a pressure operation, or otherwise.

Incidentally, it is here remarked that the externally screw-threaded portion 3 is of a taper substantially approximating that of the bore l0 and plug I2, but reversely inclined to positively ensure an absolutely liquid-proof joint within the crown-sheet 6. The fusible-bushing ll may be produced by casting, extrusion, or expanding of a suitable alloy tubing, cut to the desired lengths, and prefer-ably composed of fifteen per cent tin with eighty-five per cent lead; while there is no sweat solder bond between the shell I served that the screwthreaded portion 3, of the cast shell 9, is formed with a plain annular extension H! of less diameter, said extension having diametrically opposed notches IQ for application thereto of a conventional spanner-wrench, or other manipulator, whereby the shell I can be In addition thereto, the drop-plug l2 shell I, so as to provide an extension 2! in the firebox area to serve as a means for accelerating heat conduction to the fusible-bushing II. In

this form of the invention, an annulus 22 .of the bushing fusible composition may be extruded or otherwise applied around the plug extension 2|, as indicated in broken line section, at the base of the bore l0.

1 easily engaged in or removed from the crownsheet 6. is lengthened to project well below the tapering bore l0, into the cylindrical hollowZD of the From the foregoing it will be readily apparent that inthe event of low water in the boiler, or over the crown sheet 6, which results in uncovering the top portion [3 of the drop-plug I2, the fusible bushing I I, that normally is mechanically held to the shell I and said plug, becomes overheated sufficiently to melt and releases the dropplug l2, whereupon the latter is blown out by steam pressure in the boiler into the firebox, it being, obvious that the tapering formation of said plug efiectively prevents creeping or sticking; as well as greatly facilitating its release when the fusible-bushing commences to melt.

Having thus described my invention, I claim:

A drop plug for attachment in the crown sheets of boiler furnaces comprising an annular component having a uniformly and downwardly tapered bore, a conformatory bushing of fusible material and even thickness fitted in said bore, and a frusto-conical plug of complemental taper engaged in the bore of the fusible bushing, said plug having its larger end of slightly less area than that of the smaller end of the aforesaid annular component bore.

ROBERT N. MILLER.

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