20 Civil _Engineering.

ing part of it, is placed a disk E, of larger diameter than the valve. The valve is placed on a spindle F, to which is attached a weight o, which loads the valve. The weight G may be made in any form conve- nient when acting simply for a steam pressure safety valve ; but in this case, when the valve is intended to act also as a low water safety valve, the weight is made in the form of a lever, at the end of which is placed a stone float H, the combined weight of the lever, float, rods, &c., less by the weight of water displaced, being the load of the valve.

. . . . . . ---.: . . . .__

When the steam-pressure in the boiler acting on the underside of the valve ]) exceeds the load, the valve is raised ; and the steam then acting on the enlarged area of the disk •, and being, partially confined by the cup c, the valve continues to rise until a discharge of steam takes place through the pipe I, equal to the area of the pipe or valve seating.

In the case of low water in the boiler, the float sinks as the water lowers; and the increased weight at the end of the lever G brings t h e brass centre pin L to rest on the fulcrum or stirrup M, and raising the pin 2, in the loop of the valve rod, unloads the valve, leaving it free to the action of the steam ; the discharge of steam then takes place irrespective of the pressure of steam at the time or the size of the valve.

On an ImTroved Construction of Upright Steam Boilers. By Mr. TH0~AS DUNN.

The early forms of upright boilers, with chimney placed through the crown of the boiler, or in the side near the top, allowed a great portion of the heat to pass into the chimney flues. An attempt was made some years ago to retain this heat, by placing tubes of small diameter in the

On an Improved Construction of 5r2right Steam Boilers. 21

crown of those boilers; this, however, rendered it liable for dirt and sediment to collect on the top of the tube plates next the fire, causing them to burn away~ as also the ends of the tubes.

These objections led the writer to contrive a boiler which should re- tain the heat without the use of tubes, and should also cause a mixture of*the gases for the purpose of burning the smoke.

This improved upright boiler has two furnaces~ the heat and gases from each rising into the crown of the boiler, in which they meet and combine; the alternate working of the fires causing the flame from one fire to burn the smoke formed in the other, and vice versd; the heated current then turns down through a central space, passing again through the water before entering into the chimney flue. Several of these boil- ers have been made and tested," and have worked very satisfactorily. One, which has been at work nine months at the writer's works, is of the following dimensions :--diameter of Outer shell, 4 feet 6 inches; height from ground line to top of crown, 10 feet; diameter of inner fire-box, 3 feet 11 inches; width of down draft flue, 5 inches. The whole of the fire-box and boiler is of Staffordshire iron, the outer shell being ~-inch thick, and the inner fire-box and flue ~-inch thick. The heating surface measures 145 square feet, and the fire-grate is 7~ sq. feet area. The flat water spaces , forming the down draft, are 3 inches wide, and stayed with screw stays 5 inches apart, similarly to a loco- motive fire-box.

The following general ~esults were obtained in a set of experiments made with this boiler) taking the mean of three days' working with each description of coal; the steam pressure being maintained at 65 Ibs. per square inch throughout, and the temperature of the feed water at 62 ° F. :---5"90 lbs. of water were evaporated per lb. of coal, with best Lancashire coal, at 10s. per ton delivered, burning 16"48 lbs. per square foot of grate per hour; 4"38 lbs. of water were evaporated per lb. of coal with Burgy or the refuse of coal pits, at 5s. 6d. per ton de- livered~ burning 20"90 ].bs. per square foot of grate per hour. The outer shell of the boiler was not clothed~ which caused a considerable loss of heat by radiation in the experiments.

After trying several of these boilers, the writer constructed one with a circular down draft flue, for the purpose of saving the expense of stays : this plan did not give quite so much heating surface, but allowed rather more grate area ; and the results of this boiler were found very similar to those of the former experiments. The fire in this boiler is not divided, but the gases are allowed to combine in the fire-box.

This plan of boiler is well adapted for the interior of buildings~ where dust and dirt from ordinary boilers would be an annoyance, as the ash-pits are below the surface of the floor, and are made to hold the accumulation of a week's ashes. ~o external iron chimneys or pipes being required~ there is also less risk of accident by fire. The expense is not more than that of the ordinary upright boilers. These boilers have been proved with water pressure to 150 lbs. per square inch.

Proc. Insti. Mech. Engineers) London.