US1341474A - Boiler and firebox construction - Google Patents

Description

5 SHEETS-SHEET 1- ;Patemedl May 25, 192% J. McCLELLON. BOILER AND FIREBOX CONSTRUCTION.

APPLICA ION FILED MAR 31, 1915.

miawa-sfies:

J. M. MCCLELLON. BOILER AND FIREBOX CONSTRUCTION.

APPLICATION FILED MAR-31,1915- L l 04W at ntfid May 25, mm,

5 SHEETS SHEET 2- cg R J M. McCLELLON. BOILER AND FIREBOX CONSTRUCTION.

APPLICA ION FILED MAR 31, I9l5.

Patented May 25, 1920.

5 SHEETS-SHEET 3.

J. M. McCLELLON.

BOILER AND FIREBOX CONSTRUCTION.-

APPLICATION FILED MAR 3I, 1915.

1,341,474.. Patented May 25, 1920.

5 SHEETS-SHEET 4 mimwsewsr Inventor. g A M aimsfljlcflieiion,

Patented May 25, 1920.

5 SHEETS-SHEET 5- 1. M. McCLELLON. BOILER AND FIREBOX CONSTRUCTION.

APPLICAT ON FILED MAR-3i, 1915.

Ed m zw 9Q Waimesses:

l'lffllD SATFQS BOILER AND FIREBCX. CONSTRUCTION.

earner.

Application filed March 81, 1915.

To all whom it may concern: I

Be it known that 1, James M. hl oCLnn- LON, a citizen of the United States. and reeldent of Everett, in the county of Middlesex and Commonwealth of Massachusetts, have invented an Improvement in Boiler and Firebox Constructions, of which the following description, in connection with the accompanying drawings, is a specification, like characters on the drawings representing like parts.

This invention relates to locomotive and other boilers and among other objects provides a strong and efficient construction whereby water may quickly be converted into superheated steam, with a minimum expenditure of fuel.

The character of the invention may be best understood by reference to the following description of an illustrative embodiment thereof, shown in the accompanying drawings, wherein:

Figure 1 is a view partly in elevation and partly in section of the rear end of an illustrative boiler shown herein as embodying the invention;

Fig. 2 is a vertical longitudinal section taken on the broken line 2-2 of Fig. 1;

Fig. 3 is a vertical transverse section taken on the broken line 3-3 of Fig. 2;

Fig. l is a vertical transverse section taken on the line al Fig. 2;

Fig. r is a detail to be referred to;

Fig. 5 is a side elevation of a portion of the boiler showing one of the superheater manifolds with its cover plate removed;

6 is an end elevation of a modified construction showing the fire door contain ing portion the rear wall;

Fig. 7 is a section taken on the broken line 7'l' of Fig. 6; and

Fig. 8 is a side elevation of one of the manifolds of the superheater with its cover plate removed.

Referring to the drawings, 1 (Fig. 2) designates a barrel having at the rear end thereof a flue sheet 3 apertured to receive flu es These fines are closely arranged and distributed from the bottom to the top of the barrel thereby providing an extensive area of heating surface. In the usual boiler the barrel and its lines serve as the steam generator, but herein they constitute a feed water heater or economizer. The water is co noted from the latter to the steam genr to be described.

Specification of Letters Patent.

Patented May 25, 1920..

Serial No. 18,399.

Associated with the barrel is a fire-box comprising a crown including large drums '7, having bumped heads 9 and 11 riveted in the front and rear ends thereof. The front heads are provided with man-holes having removable covers 13.

Since the barrel serves as the feed Water heater it preferably is maintained full of water. To facilitate this the water level in the crown drums should be above the water level in the barrel. Accordingly, the drums are located above the barrel. They are shown extended forward beyond the flue sheet of the barrel to overlap the latter a substantial extent and are riveted thereto. To contribute to the support of said drums, saddles 15 are provided, riveted to said crown drums and to the barrel. These saddles may be of cast steel or other appropriate material and preferably are provided with strengthening ribs 17.

The inner sides of the crown drums preferably are flattened and apertured to receive nipples 19 Fi 3), the flattened sides of said drums being riveted together. Adjacent the bottom of the lire-box are drums 21., each having shell portions substantially of circular arc form, riveted together, one being relatively thicker than the other. The rear ends of the lower drums are closed by bumped heads 23, and the forward ends of said drums are closed by bumped heads 25 (Figs. 2 and 5), provided with man-holes having removable covers To provide a strong construction, preferably the lower drums are extended forward beyond the ilue sheet of the barrel to overlap the latter a substantial extent, and are secured to said barrel by saddles 29 in a manner substantially similar to that described for the crown drums.

The feed water is conducted from the top of the barrel directly to the lower drums 21. To accomplish this pipes 31 are provided having ends threaded into apertures in the flue sheet adjacent the top of the barrel, and other ends ronneeted by elbows 33 with pipes which diverge downward and have their lower ends expanded into apertures in the lower drums.

An important feature of the invention relates to an arrangement of steam generating tubes within and extending nearly the length of the firebox. These tubes are arranged in groups, one of which comprises a series of tubes 37 (Fig. 3) having their lower ends expanded into the lower left drum 21 and their upper ends expanded into the left upper crown drum 7.

A similar set of tubes 39 is provided at the right of the fire-box, the lower ends of the tubes of this set being expanded into the lower right drum 21, and their upper ends being expanded into the right upper crown drum 7. Preferably the portions of the crown drums in which the tubes are expanded are thickened somewhat to providethe necessary strength of material.

The side walls of the fire-box comprise series of tubes 41 having their lower ends expanded into the lower drums and their upper ends expanded into the crown drums. Preferably these side tubes are bulged outward somewhat in order to provide greater spaces between them than between the tubes 37 and 39. The spaces between the tubes 41 receive fillers 42 welded thereto. The side tubes may be covered by plates 43 (Figs. 1 and 3) if desired.

Centrally within the fire box are series of tubes 45 connected to the lower drums and the crown drums. Preferably they are somewhat larger than the tubes 37, 39 described because they are subjected to the highest heats and generate steam more rapidly than the other tubes. Also they serve to support baflie walls to be described. The water is conducted by the steam gencrating tubes from the lower drums to the crown drums and in the course of its transit is subjected to the high heats of the products of combustion within the fire-box.

The tubes 37 and 39 preferably are disposed in staggered relation and incline from the lower drums inward toward the center of the fire-box and thence upward to the crown drums. Thus they are distributed substantially entirely across the path of the products of combustion of the fire in their transit from the grate to the flue sheet and are thoroughly heated.

By arranging the steam generating tubes with the ends of one group connected to the upper and lower drums at one side of the fire-box and the ends of the other group with the upper and lower drums at the opposite side of the fire-box, it is possible to dispose the tubes of each group in staggered relation. Thus the maximum steam generating surface is obtained in a minimum space. This compact arrangement enables the extensive steam generating surfaces to be located centrally within the firebox where they meet the hottest heats and are most effective in generating steam. The disposition of the tubes is such that the gases of combustion will pass at right angles to the lengths of the tubes and since the latter are staggered the gases are obliged to pass between them in sinuous paths and bolts 51.

to brush around the circumferences of the tubes and effectively heat the same.

While the steam generating tubes are compactly arranged yet there are sufiicient spaces between them to permit the proper passage of the gases. The tubes which are farthest from the center of the fire-box have greater spaces than the tubes which are nearest the center of the fire-box and therefore offer less obstruction to the passage of the gases of combustion.

The rear wall of the fire-box comprises a lower drum'or header 47 (Fig. 1) formed to present seats 49 for receiving the lower drums which are secured thereto by stud To permit water to pass from said drums to the header, they are apertured as at 53.

The header 47 may conveniently be a steel casting having integral therewith a boxlike section 52 formed to present a firedoor 54. The portion of this casting connecting the box 52 with the header 47 is provided with a series of cells or passages 55 providing communication between said header and the spaces in said box surrounding the fire door. A series of tubes 56 is provided with their lower ends expanded in apertures in the top wall of the box section 52, and their upper ends expanded in the crown drums 7 referred to. To permit access to the lower ends of said tubes for the purposes of expanding them in the top wall of said box, or for replacement or repair, said box is provided with a removable cover plate 57 bolted thereto.

The cells 55 and tubes 56 will permit a circulation of water from the header 47 upward around the fire door to the crown drums, thereby heating the water in its transit and preventing the burning of the casting forming the fire door.

4 The cells 55 and tubes 56 also constitute a portion of the rear wall of the fire box. The remainder of this rear wall comprises a series of tubes 58 having their lower ends expanded in apertures at the top of the header 47 and their upper ends expanded in said crown drums. To permit access to the lower ends of the tubes 58, the lower side of the header 47 may be provided with apertures normally closed by plugs 59. These also may serve to permit the cleaning of said header. The ends of said header may have apertures containing plugs 61 threaded therein further to facilitate the cleaning of said header. The spaces between the end wall tubes may be filled with tiling or asbestos 63 covered by a plate 65.

The rear wall tubes 56 and 58 preferably aretapered individually and as an assembly upward toward the crown drums permitting a desirable compact arrangement and uniform distribution thereof.

In some cases, it may be desired to use a eanne modified formof rear wall structure, such as shown in Figs. 6 and 7. This structure comprises a header 67. of cast steel or other appropriate material having a box 69 of pressed steel secured thereto by stud bolts, said box being formed to provide a fire door 71. The lower side of this box is. connected by nipples 73 with the header 6 and the upper side of the box may be connected to the tubes 55 described. The entire rear face of the box may be covered by a plate 73. bolted thereto, said plate having an aperture 75 registering with a fire door 71.

The fire box may be provided with a grate com-prising usual bars 77 suitably supported. An important feature of the invention relates to means for bafliing or directing the products of combustion from the grate to the steam generating tubes, so the latter may be capable of the maximum steam generating effect. To accomplish this, a bridge wall 79 (Figs. 2 and. is provided,

preferably of strong, refractory fire clay tile provided with tongue and groove connections. This bridge wall is located at the forward end of the fire box a substantial distance from the flue sheet and is mounted on a plate 81 riveted to the under side of the barrel. This plate 81 is lined with tiles 88 and 85 of similar material to the tiles T9, and depends downward somewhat beneath the barrel.

The spaces at the lower sides of the firebox beneath the drums 21 are closed by plates 87 having flanges riveted or bolted to the under sides of the lower drums and flanges resting on transverse base bars 89 mounted on the longitudinal members 91 of the locomotive frame. The plates 87 may be lined with fire clay tiles 93.

The bridge wall extends up from the lower side drums with its top edge inclining inwardly toward the center of the fire-box, preferably following the lines of the inwardly converging steam generating tubes as referred to. The top of the bridge wall terminates substantially midway of the height of the barrel.

To further bafiie the products of combustion coming from the grate, walls 95 are provided comprising tiles supported on the lower inclined portions of the steam generating tubes 45 and following the lines of inclination of the top of the bridge wall. These baflie walls extend rearwardly a substantial distance from the bridge wall, as shown in Fig. 2.

The gases of combustion evolved from the fire on the grate are caused by the bridge and battle walls described to pass back around the rear edges of said baffle walls, thence dividing and passing forwardly and upi vardly through the spaces between the steam generating tubes 37 and 89. They pass first through the spaces between the lower portions of said tubes and thence upward through the spaces between the upper ends of said tubes. It will be observed that the disposition of the steam generating tubes above the bridge and; baffle walls is. such that they are distributed. to cover substantially the entrances of all of the fines above said bridge and baflie walls. As stated, the spaces between the outermost tubes are larger than the spaces. of the other tubes to provide a freedom of passage thereat to compensate for the greater draft adjacent the center of the fire box.

An important feature of the invention relates to the construction of a superheater and its location in the path of the gases of combustion in their transit from the grate to the barrel fines. The superheater comprises an assembly of tubes 97 extending transversely across the fire-box and having their ends expanded in the inner walls of manifolds. 99 and 101 provided with cover plates 103 and 105 detachably secured thereto. Preferably the tubes 97 are curved so. as to sag downward somewhat to permit their expansion and contraction without disturbing their connections with the manifolds.

The superheater tubes together with said manifolds. constitute a unit which may be readily removed from the fire-box through a side thereof for purposes of replacement or repair. To accomplish this the left crown and lower drums (Fig. 4) are provided with ribs or lugs 107 projecting toward one another. The manifold 99 fits between these lugs and the cover plate 103 thereof is extended beyond the manifold to overlap said lugs and is detachably secured thereto by stud bolts 109.

The crown and lower drums at the right of Fig. l are provided with ribs or lugs 111 projecting therefrom similar to those described and the manifold 101 is provided at its upper and lower ends with flanges 113 overlapping said lugs and detachably secured thereto by stud bolts 115.

By this construction when it is desired to remove the superheater unit the cover plate 103 of the manifold 99 is first removed, thereby freeing said manifold from the lugs 107. Then the stud bolts 115 are removed, thereby freeing the manifold 101 from said lugs 111. Then the superheater unit may be moved bodily out of the fire-box through the right side thereof. This will permit a very ready access to the superheater for purposes of replacement and repair without substantial disturbance to the other parts of the fire-box. For ordinary repairs, however, it would not be necessary to take the snperheater unit out of the fire-box since convenient access is had to the ends of the superheater tubes merely by removing the cover plates of the manifolds.

The steam to be superheated is conducted several times across the fire box.

- erally across from the crown drums to the superheater. To accomplish this, within the crown drums are mounted large, L-shaped steam inlet pipes 117 (Fig. 4) having their upper ends adjacent the tops of the crown drums well above the level of the water therein. These pipes communicate with pipes 118 and 119, secured to the outer side of said crown drums and depending downward therefrom, the lower ends of the pipe 118 being connected to a neck 121 (Fig. 5) projecting from the cover plate of the manifold 99 and the pipe 119 being connected to a neck projecting from the rear end of the manifold 101.

In order that the steam may be thoroughly superheated preferably it is passed To accomplish this, the manifold 99 is provided with a partition 123 (Fig. 5) extending about half way of the length thereof, and a partition 125 extending transversely across the manifold at the end of the partition 123. This divides the manifold 99 into upper chambers 127 and 129 and a'larger lower chamber 131.

The manifold 101 (Fig. 8) at the opposite side of the fire-box is provided with a partition 133 extending the length thereof and dividing the same into two chambers 135 and 137 extending the length thereof.

To deliver the steam from the superheater manifolds they are provided with necks 139 connected to pipes 141 which may communicate with the locomotive cylinders or other devices, as desired.

The steam on entering the manifold 99 passes first into the chamber 127 thereof, thence through the superheater tubes across the fire-box to the chamber 135 of the manifold 101. It passes downward in said chamber and thence through superheater tubes back across the fire-box to the chamber 131 of the manifold 99. The steam passes latthe chamber and thence through superheater tubes again across the fire-box to the chamber 137 in the'manifold 99. Some of the steam then passes outward through the delivery pipe 1&1 at the right of the fire-box (Fig. 4) and some of the steam passes again through superheater tubes across the fire-box to the chamber 129 and the manifold 99 and out through the delivery pipe 141 at the left of the fire-box.

The steam entering the manifold 101 passes first into the chamber 135 and thence downward in said chamber through superheater tubes across the firebox to the chamher 131 in the manifold 99, thence through superheater tubesagain across the fire-box to the chamber 137 in the manifold 101.

It rises in this chamber and part of it passes out through the delivery pipe 1 11 at the right of the fire-box (Fig. i) and part of it passes through superheater tubes across the fire-box to the chamber 129 of the manifold 99 and out through the delivery pipe 141 at the left of the fire-box.

The throttle (not shown) may be connected either to the inlet pipes 117 within the crown drums or to the pipes leading to the superheater or to the pipes leading from the superheater, as desired.

In operation the water to be converted into steam is forced by a usual inspirator into the barrel. It passes thence from the top of the barrel down through the pipes leading to the lower drums of the fire-box. It then rises upward through the steam generating tubes into the crown drums. The steam rising into the space above the water line in the crown drums passes thence down into the superheater and is led from the latter to the locomotive cylinders.

In conducting the water progressively as described, there is obtained a highly desirable uniform circulation providing a continuous supply of steam of uniform character.. The gradual raising of the temperature of the water in its transit as described prevents any sudden variation in the temperature of the parts of the boiler and thereby prevents the setting up of any stresses which would strain the parts and be likely to cause leakage and necessitate repairs.

The principal elements of the boiler are cylindrical and consequently the pressure therein tends to cause them to maintain their original shape, it being a well known fact that pressure in a container tends to cause the same to assume a form that is circular in cross section.

The steam generating and superheating tubes, the crown drums and the barrel, being cylindrical, require no staying. The heads of the drums being bumped are so stiff they require no staying, and the heads of the barrel are sufficiently stiffened by the closely arranged flues, which are throughout the areas of the heads. It is recognized that stays are very objectionable in boilers, but by my construction it will be apparent the necessity for the use of stays has been eliminated. It is, in fact, a stayless boiler.

- The utilization of the barrel and its flues as a feed water heater makes available a large volume of water in readiness to be converted into steam. Since the highest heats have been abstracted from the gases of combustion before they enter the barrel fines, there will be a uniform heating of the feed water and no sudden temperature changes to cause expansion or contraction of the fines, which if existing would be likely to strain and loosen the connections of the fiues with the flue sheet and cause leakage.

Since the feed water heater is so large the water remains therein a sufficient length'of time to allow sediment, mud, mineral and distributed other substances time to graviate down to the bottom of the barrel. Also the feed water in the barrel is raised to such a high temperature that impurities in the water are precipitated therefrom. Therefore the impurities in the feed water remain behind in the barrel and may be cleared out therefrom through a man-hole conveniently at the forward end thereof while the pure water passes on and is fed into the steam generator. As a result, the depositing of the impurities in the form of scale and incrustation within the drums and steam generating tubes is prevented.

The products of combustion in passing over the bridge wall come more directly in contact with the upper portion of the superheater. The lower portion of the heater extends downward a substantial distance beyond the top of the bridge wall, and leaves a large space or pocket beneath it between the flue sheet and the bridge wall. This space unobstructed by superheater tubes contributes to the producing of a strong draft which draws and deflects downward some of the products of combustion and insures the proper heating of the lower part of the superheater. 0

The superheater may not only be readily removed to repair the same, but also to provide a large open space in which a workman may comfortably and conveniently repair the barrel flues at the flue sheet.

The baffling of the gases as described increases the flame length within the firebox and enables a very effective utilization of the gases of combustion by the steam generating tubes. The gases are further effectively utilized by the superheater after pass ing the steam generating tubes. By the time the gases reach the fines the combustion will be substantially complete, but if there are any unconsumed particles carried along they will be substantially checked by striking the superheater tubes which extend across the entrances to the fines. These particles thus checked drop into the pocket beneath the superheater and may be removed through a suitable door at one end thereof.

Since the crown drums are not arranged end for end with the barrel they may be located to provide the proper depth of firebox. Thus the necessity for a throat sheet is eliminated and the crown drums may be connected directly to the shell of the barrel.

The lower drums, the upper drums, the steam generating tubes, the superheater and the side and rear walls of the fire-box constitute one unit and the barrel and its contained tlues constitute another unit. These units are connected, but are free to expand or contract away from theplace of their union, and hence will not develop distorting or injurious strains in the structure.

The arrangement of the elements of the boiler is such that the heating surfaces will absorb the maximum amount of heat from the gases of combustion. There is a continued drop in the temperature of the gases of combustion as they pass from the grate through the fire-box past the steam generating and superheating tubes through the barrel fines. On the other hand, there is a continued rise in temperature in the water as it passes from the barrel past its flues into the steam generating and superheating tubes. Thus the coolest water meets thecoolest gases of combustion and the temperature differences between the heating and heated media are reduced to a minimum. Consequently the process of generating steam from the water is carried on with high efficiency.

It is desirable to maintain the crown of the fire-box continuously covered with water to prevent any possibility of its being burned out. Crowns may be become uncovered by the permitting of the water to drop too low or by longitudinal surging of the water as when the locomotive is passing down steep grades or by lateral surging as when following a banked track on a curve. in accordance with the usual firebox construction the water is free to flow to and from the space above the crown and the top of the barrel of the boiler. In the standard boiler the length from front to rear of the watercontaining space is from 34 to 40 feet. With this freedom of wash through this length of space it frequently happens that the water drops so low that its level is not registered in the water gage. Consequently, the engineer is unable to know how high his level of water is and the crown may be uncovered for a considerable length of time and cause serious damage or accident.

By my crown construction the possibility of objectionable wash is entirely removed. The longitudinal wash is prevented for the reason that the crown drums do not communicate with the barrel through their ends, but on the contrary, are closed therefrom and their lengths are too short to permit a surge sufficient to uncover the bottoms thereof.

Also there can be no objectionable lateral wash since the crown drums furnish two chambers with a wall between them which serves as a baffle for preventing the water in one drum from flowing into the other drum sufficiently to uncover the lower fire-exposed surfaces of the drums.

Not only is the crown construction arranged to prevent the uncovering of the lower surfaces thereof which are exposed to the fire within the fire-box, but the steam generator is constructed to receive the highest beats in the fire-box at a substantial distance beneath the crown drums, so that in fact the latter might become uncovered by water and still the heat would not be great enough on the baffle walls form an arch beneath the crown drums. The products of combustion are obliged to pass rearward and spread laterally upward around the edges of the baffle walls so that the lower portions of the steam generating tubes are subjected to the highest heats. Furthermore, if the water should drop somewhat beneath the crown drums, it would still substantially fill the steam generating tubes and therefore any heat applied to the upper ends of the said tubes would be so rapidly conducted to the water therein beneath the upper ends of said tubes as to prevent any possibility of the burning-out of said tubes or the under surfaces of the crown drums. The steam generator tubes are constructed and arranged effectively to withstand the high temperatures because of their size, slope and curvature, permitting their expansion and contraction without disturbing their connections with their drums. Also as stated, merely purified water enters and passes through the tubes and therefore there will be no deposits of foreign materials therein such as would be likely to injure or weaken the same.

In locomotives the draft for the fire-box is obtained from the exhaust from the cylinders. A partial vacuum is created in the smoke-box thereby drawing the air up through the grate and the bed of coal thereon. This draws the gases of combustion from the fire through the barrel flues to the stack. The draft will be greater or less depending on the amount of obstruction in their path from the grate to the stack. In accordance with the present invention the superheater is located in the fire-box across the entrances of the barrel flues and checks the gases at this point, but to compensate for this the number of flues in the barrel is increased. As a result, the vacuum effect which formerly existed in the smoke-box is substantially transferred to the entrance to the fines. Thus a powerful draft is created at the superheater which is located at the entrance to said fines. The restriction of the flow of the gases causes their velocity to be increased in passing through the passages between the superheater tubes.

It will be observed by reference to Fig. 3 that the fire-box as a whole tapers upward and is substantially narrower at its top than at its bottom, thereby providing ample space for the forward windows of the engineers cab enabling him to easily climb out of the cab along the running boards at the sides of the barrel of the boiler while the locomotive is inmotion, r

Having described an illustrative embodiment of my invention without limiting the same thereto, what I claim as new and desire to secure by Letters Patent, is:

1. In a locomotive boiler a water tube steam generator having upper and lower chambers, a feed water heater receiving gases from the generator and being free of direct communication with said upper chamber, and a superheater comprising transversely extending steam tubes suspended between the tubes of said generator and the gas intake end of said water heater.

2. In a locomotive boiler a water tube steam generator having upper and lower chambers, a feed water heater receiving gases from the generator, said heater, being free of direct communication with said upper chamber and having a connection from the intake end thereof to'the lower chamber of the generator, and a superheater comprising transversely extending steam tubes suspended between the tubes of said generator and the gas intake end of said water heater.

3. In a firebox, the combination of upper and lower drums, groups of steam generating tubes connecting said drums, a bridge wall intermediate of the length of said firebox and baffle walls inclining inward toward one another at the rear of said bridge wall and supported by the inner rows of said groups of steam generating tubes.

4:. In a fire-box, the combination of lower side drums with crown drums, a series of steam generating tubes connecting the lower and crown drums at one side of the fire-box and a series of steam generating tubes c0nnecting the lower and crown. drums at the other side of the fire-box, said series of tubes converging inward toward the center of the fire-box and thence substantially vertically upward to the crown drums and collectively screening substantially the entire width of the upper part of said fire-box.

5. A firebox comprising a crown chamber, lower side drums and water tubes connecting the same and a superheater at one end of the firebox comprising an upright header at each side fitting between the crown chamber and a lower drum and steam tubes between said headers extending across the firebox.

6. A firebox comprising a crown chamber, lower side drums and watertu-bes connecting the same and a superheater at one end of the firebox comprising an upright header at each side fitting between the crown chamber and a lower drum and steam tubes between said headers extending across the firebox, the maximum depth of the superheater beyond one edge thereof being not greater than the distance between the crown chamber and drum adjacent said edge whereby the superheater as a whole may be withdrawn laterally.

7. A firebox comprising a crown chamber,

lower side drums and water tubes connecting the same and a superheater at one end of the firebox comprising a pair of headers and connecting transversely extending curved tubes, said superheater as a whole having substantially the form of a segment of an annulus whereby it may be laterally withdrawn by a movement of rotation and means for fixing the headers each between the crown chamber and a lower drum.

8. In a fire-box the combination of upper andlower side drums with a superheater comprising headers, tubes extending transversely across the fire-box connected to said headers and means detachably connecting said headers to said drums.

9. In a fire-boX the combination of upper and lower side drums with a superheater comprising, headers, tubes connecting said headers, covers for said headers, means detachably connecting the cover of one of said headers to the upper and lower drums at one side of the fire-box and means for detachably connecting the body of the other header to the upper and lower drums at the opposite side of the fire-box.

In testimony whereof I have signed my name to this specification, in the presence of two subscribing witnesses.

JAMES M. MGCLELLON.

Vitnesses HENRY T. vVILLIAMs, ROBERT H. KAMMLER.

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