Horizontal Water-Tube Boilers - Thornycroft-Marshall Water Tubes Nearly Horizontal Steam and Water Drum Cross Type Horizontal Curved-Type Single-Tube Non-Sectional

HORIZONTAL WATER-TUBE BOILERS - THORNYCROFT-MARSHALL: WATER TUBES NEARLY HORIZONTAL, STEAM AND WATER DRUM (CROSS TYPE) HORIZONTAL, CURVED-TYPE, SINGLE-TUBE, NON-SECTIONAL The Thornycroft-Marshall non-sectional boiler consists of a large horizontal steam and water drum, a vertical water box or header, and the generating tubes. Like the Mosher, the tubes are curved slightly, but the header is a distinct difference.

The general features of construction are shown in Fig. 57. The steam and water drum, sometimes called the separator barrel, is simply a cylinder with dished ends. The water level is about one-third the diameter of the cylinder. The tubes, which are 3i inches in diameter, are connected in pairs to a junction box at one end and to a water box or header at the other end.

Thus each pair forms a unit, but the two tubes of the unit are not in the same vertical plane. The upper tube enters the header as high as possible and the lower ones enter low down, thus giving considerable upward slope. From near the top of the water box, three rows of tubes lead to the separator barrel as shown in Fig. 58. The water box is very simple, the fiat plates 'are stayed by short hollow screw stay-bolts. The junction boxes are not restrained in any way; this construction, combined with the slight curve of the tubes, allows free expansion. The slight curve also allows the tubes to enter the separator barrel and the water box at right angles so that they may be expanded in place.

Circulation.

The feed water enters the steam and water drum and then passes to the water box through the two lower sets of tubes. See Fig. 58. The water enters the lower ends of the various pairs of tubes, as shown in Fig. 58, and rises in the tubes while in con. tact with the hot gases from the furnace. The mixture of steam and hot water then enters the header from which it passes to the steam and water drum by means of the highest row of tubes. The difference in height of the two tubes of a unit insures good circulation. A baffle plate prevents the water from splashing to the steam pipe.

The hot gases pass upward among the tubes which cross so frequently that they take almost all the heat from them.