discharged itself through the damaged one, increasing the extent of the disaster, and rendering the ship for the time helpless. Self-acting valves might therefore be of great value in a warship in action.

Valves of this description should always be placed in a horizontal

FIG. 101.

position, as when placed vertically, the pulsations of the steam cause them to work up and down on their seatings with violence, and in some cases the valves have been broken from this action.

The continuation of the valve spindle is provided with a cross handle so that the valve can be turned on its seat, and this handle also

enables the valve to be pulled open after the screw has been worked back when opening the valve. This should always be done, as otherwise the friction of the glands will keep the valve closed till the excess pressure inside is sufficient to overcome this friction, when the valve would often open with violence.

Internal steam pipes.-The stop-valves have attached to them thin brass pipes, which are carried inside across the steam chest close to the top of the boiler, and are called the internal steam pipes. They are closed at the end, but have narrow slits cut at the top, which allow the steam to enter the pipe and pass through the stop-valve to the engines. The object of this fitting is to prevent priming as far as possible, or the passage of water through the stop-valves with the steam. By spreading the area of collection of steam, the evaporation is rendered more uniform, and the tendency to priming from the rush of the steam to a single orifice is obviated. A drain hole is fitted in the pipe to prevent accumulation of water.

From the stop-valves on the different boilers steam pipes are carried, which unite at the end of the stokehold in one main steam pipe, through which the steam passes to the engines.

Bulkhead self-closing stop-valves.-In ships of the Royal Navy that have more than one boiler room, the steam pipe from each boiler room is carried independently to the engine-room bulkhead, and at the end of each pipe another self-closing valve is fitted, called the 'bulkhead selfclosing valve,' so that in the event of any steam pipe being damaged on the boiler side of this valve, only the boilers in connection with that steam pipe would be put out of action, the others remaining efficient. These bulkhead valves perform for each stokehold the same functions that the boiler self-closing valves perform for each boiler, and are constructed similarly to Fig. 105.

Arrangement of main steam pipes.-The general arrangement of the main steam pipes of vessels in the Royal Navy having several boiler rooms and two engine rooms is shown in Figs. 106 to 108. In each boiler room the steam from each boiler leads through the boiler selfclosing valves A into a common pipe which is led to the engine-room bulkhead, where the bulkhead self-closing valve B is fitted. An entirely separate pipe from each boiler room is led to the engine-room bulkhead. On the engine-room side of these bulkhead valves, the steam pipes lead into one common athwartship pipe, of reduced size, communicating with each set of engines. On each branch from this athwartship steam pipe to the main engines an ordinary screw-down stop-valve c is fitted in large vessels, which may be opened or closed by hand from the engine room and also at some position entirely outside the engine room, on one of the ship's decks, by the gear shown in Fig. 107.

This valve is intended for use in case of any accident in the engine rooms causing an escape of steam. Under these circumstances if the discharge of steam is so great as to force the engine-room staff to leave the engine room, they can proceed to the deck position and shut off the steam from the engines.

In the more recent naval engines another stop-valve D is fitted in the athwartship steam pipe at the middle line, worked from either side of the bulkhead, so that in case of any injury to the athwartship pipe the steam can be confined to one side of the ship if necessary, and thus enable one set of engines to be worked.

At the end of the branch steam pipes on each side is the regulating valve E, for the main engines, described in Chapter XV., and fitted close to the high-pressure valve casing.

The additional screw-down valve c is fitted to close with the steam

pressure to ensure tightness when closed, and to facilitate opening this valve, a small pass-valve F is fitted, by means of which the pressure on each side can be equalised, and moving the valve against the steam pressure is facilitated.

Expansion joints. As the steam pipes are subject to considerable increase of temperature when they contain steam, they necessarily

expand and lengthen, and provision has to be made to enable this expansion to take place without bringing undue strains on any part. In small pipes this can be arranged by bending them sufficiently, so that the pipe at the bend is sufficiently elastic to allow for this elongation and contraction. In large pipes expansion joints have to be fitted which enable one end of the steam pipe to slide in and out of the adjacent pipe as changes of length take place. Fig. 109 shows the usual type of expansion joint formed by a stuffingbox and gland. Care must be taken when such expansion joints are fitted in pipes having a bend, that the unbalanced force is provided for either by struts or safety stays, otherwise the bent part of the pipe may be drawn out of the other. The expansion joints in the arrangement of Fig. 108 are indicated, one being fitted adjacent to each of the boiler stop valves a, and others elsewhere.

Separator. Before reaching the engines the steam often passes through a separator similar to that shown in Fig. 110. The object is to provide an additional safeguard against priming, by preventing any water in the steam pipes from entering the cylinders. It is divided from the top to nearly the bottom by a diaphragm, D, the steam entering on one side and leaving on the other. Any water that reaches the separator is mostly left at the bottom, only the steam passing on to the cylinders. A drain-cock or valve is fitted, so that the water may be discharged by hand into the hot-well or feed-tank, and returned to the boiler. A non-return valve is fitted at the end of the pipe. The level of water is shown by a glass gauge G.

FIG. 109.

Automatic separator. In the fast-running engines of the torpedoboat destroyer type with water-tube boilers, water is occasionally passed into the steam pipes with the steam which, if it entered the

OUTLET

cylinders, owing to the great speed and light construction of the engines, would probably do considerable damage before being passed through. In the recent vessels of this class, separators with automatic blow-out apparatus are fitted, so that when any quantity of water accumulates in the bottom of the separator by priming or other means, a float is raised, which by a system of levers opens an orifice of considerable area for drainage, so that the water is very quickly got rid of.

With such machinery the old separator with hand-blow-out apparatus is of little or no value. Fig. 111 shows an example fitted in the most recent thirty-knot destroyers. It is a gun-metal casting, provided with the usual diaphragm, while hand-blow-off apparatus is fitted in addition to the automatic arrangement.