meet in the glass tube, and stand at the same level as in the boiler. The lowermost visible part of the glass tube should be at least 3 inches above the highest point inside the boiler acted on by

Section.

Sectional Plan.

GT

Outside View.

Sectional Plan through B.

GLASS-TUBE WATER GAUGE, BY SCHÄFFER & BUDENBERG.

B

the flames or hot gases, and the water should never be permitted below this point when the boiler is at work. By shutting the middle cock and opening the lower one, at the same time keeping the upper one open, steam is blown through the glass tube. By shutting the upper cock and opening the middle and lower ones, water is blown through the lower cock, &c., and by shutting the upper and middle cocks the steam and water in the boiler are cut off from the glass tube, and it may be removed for cleaning, or for replacing it by another tube. These cocks should be tried two or three times every day, and the glass tube kept thoroughly clean.

In addition to the glass-tube water gauge, three ordinary cocks are frequently fitted to the boiler in order to ascertain the height of the water in it, should the glass tube break or fail to act. The upper cock is fixed on a level with the upper screw plug, A, in the last figure, the lower one on a level with the screw plug, B, and the middle one half-way between them. Steam should issue from the boiler upon opening the upper cock, water upon opening the lower one, and steam or water, as the case may be, when opening the middle one.

LECTURE XXVII.-QUESTIONS.

1. Sketch an ordinary lever safety valve as applied to a land boiler. The diameter of a valve is 3 inches; the leverage is 11 to I. Find the pull on the end of the lever when the steam pressure is 30 lbs. above the atmosphere. Ans. 30.1 lbs.

2. Required the weight to be placed on the end of a safety-valve lever 18 inches long, diameter of valve, 24 inches, distance from fulcrum to valve, 3 inches, the upward pressure on the valve required for lifting the valve and lever being 20 lbs., and the pressure of steam in the boiler being 100 lbs. per square inch above that of the atmosphere? Ans. 95.7 lbs.

3. Steam is required to blow off at 60 lbs. by gauge. The weight to be placed on the end of an ordinary safety-valve lever is 56 lbs., the weight of the lever is 8 lbs., and the valve weighs 2 lbs. At what position on the lever from the fulcrum must the weight be placed, if the diameter of the valve is 3 inches, and if the distance from the centre of the valve to the fulcrum is 3.25 inches, while the centre of gravity of the lever is 10 inches from the same point? Ans. 27 inches.

4. What weight must be placed on a balanced lever at 27" from the fulcrum in order to just counteract steam pressure of 60 lbs. per square inch, if the radius of the valve is 1.75" and the distance from the fulcrum to the centre of the valve is 3.25"? Ans. 59.27 lbs.

5. What diameter should a safety valve have in order that steam of 100 lbs. pressure may blow off; the other sizes being the same as in Question 3? 6. Sketch and describe a safety valve loaded with direct weights, and point out what advantages it has over an ordinary lever valve.

7. If 630 lbs. dead weight is put on a safety valve 4" diameter, at what pressure will steam blow off? Ans. 50 lbs. per square inch.

8. A safety valve blows off at 25 lbs. per square inch. What is its diameter if 820 lbs. be the dead weight on the valve? Ans. 6"5.

9. What weight and bulk of lead will be required for the dead weight on a safety valve 3" diameter to blow off at 50 lbs. per square inch if the valve and spindle weigh 16 lbs. Ans. 337 lbs. ;

10. Sketch and describe a marine boiler safety valve with a spiral spring for loading the valve, and explain why this form is better than a dead weight or lever and weight for the purpose.

11. Describe the water gauge for ascertaining the height of the water in any steam boiler. Show its position with reference to the fire box of the boiler, and sketch a longitudinal section through the gauge. (S. and A Exam.. 1887.)

12. Sketch and describe the following safety valves :—

(1) An ordinary lever valve.

(2) The Ramsbottom spring loaded valve.

(3) An ordinary dead weight valve. (S. & A. Exam., 1889.)

13. Sketch a vertical section of a dead-weight safety-valve. (No marks will be given for the ordinary lever safety valve.) If the valve is 21 inches in diameter, with a dead weight of 300 lbs., at what steam pressure per square inch will the valve lift. (Take T=3.) S. and A. Exam. 1891.) Ans. 75'42 lbs.

T

14. Describe and sketch the construction of a glass water gauge and its mounting, as adapted for use in a steam boiler. Where is such a gauge placed, and at what height? How is its working tested? (S. and A. Exam. 1892.)

15. Describe and sketch a dead-weight safety valve. Such a valve is 2 inches in diameter; the weight of the valve and spindle is 20 lbs. What dead-weight would require to be added so that steam should blow off when the pressure reached 80 lbs. per square inch? (S. and A. Exam. 1894.) Ans. 24133 lbs.

16. A safety valve of 3 inches diameter is held down by a lever and weight. The lever is 30 inches long, and the valve centre is 4 inches from the fulcrum, the suspended weight on the lever being 56 lbs. At what pressure of steam would the valve be lifted, the weight of the lever being neglected in the computation? Sketch the valve, its seating, and the general arrangement. (S. & A. Exam. 1895.)

17. Sketch the construction of a lever safety valve with balance weight, and state under what circumstances such a construction could not be used. If the lever be 16 inches in length and the centre of the valve seat is 4 inches from the fulcrum, while the diameter of the valve is 4 inches; find the weight to be placed at the end of the lever so that steam may blow-off at a pressure of 45 lbs. per square inch, the weight of the valve and of the lever being neglected. (S. & A. Exam. 1896.)

LECTURE XXVIII.

CONTENTS.-Longitudinal and Cross Sections through a Modern Locomotive Boiler-Description of Boiler-Locomotive Regulator Valve and Safety Valves.

FD,
FDH,

F B,

B,

DP,

BA,

F Bx,

FTP, T,

TP,

INDEX OF PARTS TO THE LOCOMOTIVE.

Combustion and Heating Arrangements.

SB,
Cy,

SBD,

Fire-door Handle.

Fire Bars, on which the coals are placed, with spaces between them to allow air to pass up through the coals and cause combustion; and to allow ashes to fall into the ash pan. Bearers, for supporting F B at both ends.

Deflector Plate, for deflecting the gases as they rise from the
coals, and causing them to mix properly; thus ensuring a
more complete consumption of the smoke.

Brick Arch, also for deflecting the gases and preventing them
from rushing along the tubes as they rise from the coals.
Fire Box, in which the products of combustion should assume
the form of a colourless gas. Its sides are usually made of
copper, as then they transmit the heat to the water more
quickly than they would if made of iron, and resist better the
action of the fire.

Fire-box Tube Plate.

Tubes, along which the heated gases pass on their way to the
chimney, heating the water which surrounds them. They
are fixed at the one end to F Bx, and at the other to S B.
Smoke-box Tube Plate.

Smoke Box, from which the smoke passes on through—
Chimney.

Smoke-box Door, which admits of access to the boiler tubes
and steam pipes.

Boiler.

OS, for Outer Shell, in three lengths, Front, Middle, and Fire-box Shell. The front is secured to the smoke-box tube plate, TP, by an outside cylindrical angle iron. The middle length is also cylindrical, and is attached to the front length by a lap joint. The fire-box shell is cylindrical on the top, but flat on the sides, to allow of its going between the main frames, MF; it is secured to the middle length by a lap joint.