===================================================+=======+======+ TABLE | | | SHOWING THE AMOUNT OF LAP, LEAD AND TRAVEL OF THE | | | VALVES OF LOCOMOTIVES USED ON 35 OF THE RAILROADS |Outside|Inside| IN THE UNITED STATES AND CANADA. | Lap | Lap | ---------------------------------------------------+-------+------+ | in. | in. | For locomotives running express pass. trains 25 use| ⁷⁄₈ | ¹⁄₈ | „ „ „ „ „ „ 6 „ | ³⁄₄ | ¹⁄₁₆ | „ „ „ „ „ „ 4 „ | 1¹⁄₄ | ¹⁄₄ | „ „ „ accom. „ „ 20 „ | ³⁄₄ | ³⁄₈ | „ „ „ „ „ „ 10 „ | ⁷⁄₈ | ¹⁄₁₆ | „ „ „ „ „ „ 5 „ | ⁵⁄₈ | ³⁄₁₆ | „ „ „ heavy freight „ 19 „ | ³⁄₄ | ¹⁄₁₆ | „ „ „ „ „ „ 11 „ | ⁵⁄₈ | ¹⁄₈ | „ „ „ „ „ „ 5 „ | ¹⁄₂ | ³⁄₁₆ | ===================================================+=======+======+ ===================================================+======+==== TABLE | |Lead SHOWING THE AMOUNT OF LAP, LEAD AND TRAVEL OF THE |Travel| in VALVES OF LOCOMOTIVES USED ON 35 OF THE RAILROADS | of |full IN THE UNITED STATES AND CANADA. | Valve|Gear ---------------------------------------------------+------+---- | in. | in. For locomotives running express pass. trains 25 use| 5 |¹⁄₁₀ „ „ „ „ „ „ 6 „ | 4³⁄₄ |¹⁄₈ „ „ „ „ „ „ 4 „ | 5 |¹⁄₈ „ „ „ accom. „ „ 20 „ | 5 |¹⁄₁₀ „ „ „ „ „ „ 10 „ | 5¹⁄₂ |¹⁄₁₆ „ „ „ „ „ „ 5 „ | 4¹⁄₂ |¹⁄₈ „ „ „ heavy freight „ 19 „ | 5 |¹⁄₁₀ „ „ „ „ „ „ 11 „ | 4¹⁄₂ |¹⁄₁₆ „ „ „ „ „ „ 5 „ | 4³⁄₄ |¹⁄₁₀ ===================================================+======+==== QUESTION 238. _What should be the width of the bridge between the steam and exhaust ports?_ _Answer._ It is usually made about the same thickness as the sides of the cylinder, in order to secure a good casting; but sometimes it is necessary to make it wider, in order to prevent steam from escaping from the steam-chest into the exhaust, which is apt to be the case if a valve has little lap and a long travel. QUESTION 239. _What determines the width of the exhaust-port?_