276 



CASSELL'S POPULAR GARDENING. 



High.- pressure valves should always be used where 

 boilers are coupled together, in all mains, and 

 wherever it may be thought desirable to effectually 

 shut back the water in case of break- down or acci- 

 dent. The thi-ee valves (Figs. 52, 53, 54) manu- 

 factured by Foster and Pearson, of Beeston, to which 

 the Horticultural Society's medal has been awarded, 

 are admirably suited to this purpose, as they answer 

 the two-fold purpose of valve and stop-tap. 



Valves are sometimes placed in front of H -pieces 

 (Fig. 55) when a flow and return pipe run through 



Pi^ 55.— H-piece with Valves. 



several compartments, say a, b, c (Fig. 56); by 

 placing the castings, say at o, a can be heated by 



A 





B 



C 







O P 



Fig, 56.— Heating Compartments separately. 



shutting the valves, a I, while b and c remain cold. 

 By opening them at o, and closing them at p, a and 

 B can be heated, while c remains cold ; and by open- 

 ing aU the valves, the three sections will be heated. 

 H -pieces are often made with valves at c.but with an 

 air pipe at the extreme limit of c, these are of no 

 practical value. 



Boilers. — The number of these before the public 

 is now very great, and, at first sight, almost for- 

 midable ; but when classified and divided into three 

 or four sections, to which nearly all of them belong, 

 the difficulty in choosing a boiler for any special 

 purpose is not so great as many imagine. 



The power of a boiler depends upon the area of 

 heating surface, and the amount of heat given out 

 depends upon the position of that surface, and the 

 way in which a boiler is stoked. If every square 

 foot of eiiective heating surface in a boiler is equal 

 to the heating of forty to fifty feet of four-inch 

 piping, and fifty to sixty feet of three-inch, it is easy 

 to decide upon the boiler capable of doing the work, 

 provided always that we take oil thirty per cent, of 

 the manufacturer's calculation, and take two boilers 

 to heat, say, one thousand feet, when one is repre- 



sented as being capable of doing the work. Then, 

 were two forms, one more simple than the other, 

 presented for our approval, we should not go far 

 wrong in choosing the simplest form, affording the 

 largest surface for the fuel to act upon in a direct 

 manner. 



Makers of boilers often prejudice themselves, and 

 disappoint the public, by specifying the quantity of 

 piping their boilers will heat when everything is 

 fi-esh, clean, and new, the interior free from incrusta- 

 tion, and the flues clear of dust. Driving, however, 

 does not mean economy of fuel, and, as all practical 

 men are anxious to obtain an apparatus that will do 

 the greatest amount of work- at the smallest outlay 

 for fuel, or for repairs in case of accident, a boiler 

 capable of heating fifty per cent, more piping than is 



Fie-. 57.— Plain Saddle Boiler. 



likely to be attached should always be selected, as it 

 will be found the cheapest in the end. 



The following table gives the maximum quantity 

 of pipe which a boiler will heat, supposing the best 

 fuel only be used ; everj'- square foot of boiler ex- 

 posed to the direct action of the fire being equal to 

 three square feet of fine surface : — 



Surface of Boiler exijosed 



to the direct action 4-iii. pipe. 3-iii. pipe. 2-in. pipe, 



of the fire. 



4 square feet will heat 200 feet, or 266 feet, or 400 feet. 



6 „ 300 feet, or 400 feet, or 600 „ 



8 „ „ 40~> feet, or 533 feet, or 800 „ 



10 „ „ 500 feet, or 666 feet, or 1,000 „ 



14 „ „ 700 feet, or 933 feet, or 1,400 „ 

 20 „ „ ],000 feet, or 1,333 feet, or 2,000 „ 



A small apparatus ought always to have more sur- 

 face of boiler in proportion to the length of pipe 

 than a larger one, as the fire is less intense, and burns 

 to less advantage, in a small than in a larger furnace. 



The Saddle Boiler is too weU known to require 

 description. The plain saddle (Fig. 57) is the type 

 of a great number of boilers, which cannot easily be 

 beaten. It is made in cast and wrought iron, welded 

 or riveted. Wrought-iron boilers, although more 

 subject to incrustation, are generally chosen in pre- 

 ference to cast, and when well set over a fire-place 

 composed of fire-bricks, and properly stoked, they 

 are sure to give satisfaction. An improved form of 



