Chapter 131

[58]Seepage 383for the construction of a link motion.

In proportion as the link block is (by moving the link endways) brought nearer to the middle of the link, the valve travel is reduced and the point of cut off is hastened, thus increasing the expansion.

When the link block is in the middle of the link, the latter is in mid gear, and the valve only opens the ports to the amount of the lead, and the link action is the same, whether the engine moves backwards or forwards.

The motion of the link is as follows:

The two ends are vibrated by the eccentrics from the central pin of the link hanger (or suspension link) as a centre of motion, while at the same time this end of the link hanger swings in an arc of which its other end is the centre of motion.

In small engines the link is sometimes used for varying the expansion as well as for reversing the direction of engine revolution.

In large engines it is used for reversing only, a separate expansion valve being used for varying the point of cut off.

In small engines the link is moved endwise for forward or backward gear by a simple arrangement of hand levers. In large engines these levers are supplemented by a worm and worm gear, and in still larger engines a steam reversing gear is used for shifting the links from forward to backward gear, or vice versa.

When there is no link motion, a Joy valve gear, a Marshall valve gear, or a loose eccentric may be used. A loose eccentric is one that can be moved around the shaft to reverse the engine. It may be moved around the shaft by mechanical means, or the eccentric rods may be disconnected, and the valve worked by hand, to cause the engine to run in the required direction, until a pin fast in the shaft meets a lug on the eccentric and drives it, there being two such lugs or shoulders spaced the requisite distance apart on the eccentric. This plan is obviously only suitable for small engines.

A separate expansion valve is a valve employed to effect the cut off and vary the expansion. It does not affect either the admission or exhaust of the steam to the cylinder.

It is used because by its means an early point of cut off and high rate of expansion may be obtained with a fixed point of exhaust, a fixed amount of compression, and a fixed amount of lead, whereas with the link motion alone the exhaust occurs earlier in the stroke, and the compression and the lead increase as the link is moved from full gear towards mid gear. The expansion valve should, when the engine is to be started, be set for the latest point of cut off. The eccentric for the expansion valve is set opposite to the crank, in order that its action may be the same, whether the engine runs backward or forward.

The small cylinders on top of the steam chests are for the purpose of guiding the upper ends of the valve spindles, and are fitted with pistons having steam beneath, the space above being in communication with the condenser. The steam pressure on the piston supports the weight of the valves and valve gear.

The friction of a slide valve may be relieved or reduced by excluding the steam from its back, which is done by various means, such as by a ring cast on its back and working steam tight against a plate held independently of the valve. The interior of the ring should be open to the exhaust.

The friction of a slide valve is caused by the steam pressing it to its seat, the amount of this pressure varying with the fit of the valve to its seat, and its position over the ports, or, in other words, upon how much of the valve area has steam pressing on one side only.

The travel of the eccentric rod is the distance it moves measured on a straight line. It is equal to twice the throw of the eccentric.

The throw of an eccentric is the distance between the axis of its bore and the centre or axis from which its circumference was turned in the lathe.

Double beat valves are composed of two discs or mitre valves, one above the other on the same stem, so that as the steam presses on the opposite faces of the two discs the valve is balanced. The objection to their use as safety valves is, that they are balanced and would not lift unless the area of the upper disc was made larger than that of the lower one, in which the objection would remain that the two discs do not expand equally, hence they are apt to leak. They are sometimes used instead of slide valves, but are objectionable because a separate admission and exhaust valve is required at each end of the cylinder, and because at quick speeds of revolution they fall to their seats with a shock or blow which wears out both the valve and the seat. When a high piston speed is obtained by great length of piston stroke, and not by high rotative speed, their use is less objectionable.

Expansion joints are joints which permit the parts they connect to expand and contract without straining them. They are necessary on the steam pipe connecting one boiler to another, and on the main steam pipe from the boilers to the engine. The working surfaces require to be of brass, so that they will not corrode.

They require the collar on the internal pipe of the joint (on which the gland fits) to be permanently fixed by soldering or brazing, and check nuts on the studs, so that the internal pipe shall not be blown out from the steam pressure.

This pipe is also sometimes fitted with chains or stops, in case the studs should break, or the nuts or collar strip.

An oil cup is either a cavity cast in the piece or a cup shaped vessel or hollow cylinder screwed in. It contains a pipe extending up about three-fourths of its height, and through this pipe the oil is fed to the surface required to be lubricated. A hinged lid or, in some cases, a screwed cap covers the oil cup to exclude dust, etc.

The syphon or worsted consists of a number of threads of worsted or lamp wick of equal lengths; a piece of lead or copper wire is laid across the middle of the worsted, the copper wire is doubled and twisted and is then pushed down the tube, carrying the doubled end of the worsted with it. The upper ends of the wire are bent over the end of the tube so as to hold the worsted, whose lower end should pass down below the level of the bottom of the oil cup. The oil feeds (on the syphon principle) through the medium of the wick or worsted, which should not fit the tube tight but quite easily, its upper ends hanging over the top of the tube to the bottom of the cup.

The worsted may be cleaned with scalding water, or by water thrown upon it from the boiler.

Tallow cups for high pressure cylinders must have two cocks, so that after the cup is filled the top cock may be closed and the bottomone then opened. The top cock prevents the tallow or oil from being blown out of the cock by the steam. For the low pressure cylinder a cup with a single cock will answer, as the cock may be opened when the vacuum is at that end of the cylinder, and the air will force the oil or tallow in.

A steam lubricator or impermeator is an automatic oil feeding device placed on the steam pipe of the high pressure cylinder. Steam lubricators are made in various forms, some having a positive feed by a pumping arrangement, while in others the oil floats upon water in the body of the lubricator to which steam is admitted; the condensation of the steam increases the quantity of water and causes the floating oil to overflow and feed through a pipe leading into the steam pipe or steam chest, as the case may be. Cooling the impermeator causes more rapid condensation, and increases the amount of oil fed to the steam.

Cylinder escape or relief valves do not let all the water out of the cylinder because of the clearance,[59]hence the amount of water left in will equal the amount of clearance.

[59]Seepage 372, on clearance.

The small cylinders on top of the steam chest are for the purpose of guiding the upper ends of the valve spindles, and are fitted with pistons having steam beneath, the upper end being in communication with the condenser.

The effort of the piston to rise supports the weight of the valves and valve gear.

The valves of a marine engine that are worked by hand are, the stop valves for letting on steam from the boiler, the safety valve, which is lifted to see that it is in proper working order, the Kingston valve for letting in the circulating water, the blow through or starting valve for warming the cylinders and starting the engines. The valve for adjusting the rate of boiler feed has its lift adjusting screw operated by hand. The slide valve may also be operated by hand before the engine is started, or it may be operated by a steam reversing gear. The expansion valves are also set by hand to regulate the point of cut off or amount of expansion. The valves that are operated automatically, or from the motion of the parts, are the slide and expansion valves, the suction and delivery and check valves of all pumps, the air pump bucket valves, the snifting valves, and the ship’s side overboard discharge valves. When the engine is stopped and the steam shut off, close the dampers to check the draught and open the drain cocks on the high pressure cylinders.

If the engine is soon to start and the pressure in the boiler is at the blowing off point, start the boiler feed, if the height of the water in the boiler will permit it, and this is a good time to clean the fires. If the engine is to stop for any length of time, shut off the impermeator and the injection supply.

A vacuum gauge is an instrument for measuring the total or absolute pressure, or pressure above a perfect vacuum, and it is used to indicate the degree of vacuum that exists in the condenser, which, when the various joints about the cylinder and condenser are tight, averages about 27 inches of mercury when the temperature in the hot well is about 100° Fahrenheit.

In round numbers a column of mercury 32 inches high equals the weight of the atmosphere,[60]hence taking the weight of the atmosphere at sea level to be 15 lbs. per square inch, then each two inches of mercury represents an atmospheric pressure of 2 lbs. Suppose then that a bent U shaped tube, each leg of which is 30 inches high, is half filled with mercury, and that one end is in communication with the condenser, and the other end is open to the atmosphere, and if there was a perfect vacuum in the condenser, the pressure of the atmosphere in the open leg would force all the mercury into the leg that communicated with the condenser, hence there would be a column of 30 inches of mercury in one leg, and air in the other.

[60]See“Barometer,”Chapter XL.

If there was in the condenser a pressure of 11⁄2pounds per square inch above a perfect vacuum, the mercury would stand 27 inches high in one leg, and 3 inches in the other, and so on, hence from the height of the column of mercury above its natural level the degree of vacuum in the condenser may be known. But the pressure of the atmosphere varies with its temperature, and the weight of mercury also varies with its temperature.

To find the total pressure in the condenser, therefore, we subtract height of the column of mercury given by the condenser from the height of the column in the barometer, and divide the remainder by 2.

Examples.—The barometer stands at 29.5 and the vacuum gauge at 26, what is the absolute pressure in the condenser?

Here,

29.5 - 26 = 3.5 ÷ 2 = 1.75Answer, 175⁄100lbs. per square inch.

A dial vacuum gauge of the Bourdon construction is similar to the Bourdon steam gauge, that is used upon the boiler, except that the inside of the elliptical tube is in communication with the condenser and the atmospheric pressure bends the tube into a curve of smaller radius (instead of to a larger one, as in the case of the steam gauge).

Obviously, therefore, the zero of the dial vacuum gauge is atmospheric pressure.

Suppose the dial vacuum gauge shows 10 lbs., the steam gauge 120 lbs., and the barometer 15 lbs., and we may find the total pressure or pressure above vacuum of the steam in the boiler is as follows:

To make the correction necessary because there is not a perfect vacuum in the condenser, we then proceed as follows:

Then

Racing means a sudden acceleration of the engine speed, and occurs when the propeller is not fully immersed in the sea, as by reason of the pitching of the ship. Racing augments the strain on the working gear of the pumps, and is likely to lead to accident. It is obviated by the use of a governor or by partly shutting off the steam by hand.

A marine governor is a device for controlling the engine speed, by reducing the supply of steam to the engine cylinder whenever the engine begins to race. The governor is driven by band or rope on the crank shaft. Governors are made in various forms; thus, in one the shaft has a fly wheel and a friction clutch, one half of which is fast on the governor shaft, while between it and the other is a spiral spring which connects the two halves. If the speed accelerates, the sliding half of the clutch is moved along the governor shaft, and by means of links it closes the throttle valve of the main steam pipe, thus wire drawing the steam, reducing its pressure and thereby controlling the engine speed.

A common paddle wheel has a cast iron centre into which the wrought iron arms are set and secured by wrought iron bolts and nuts.

The bolts have hook heads to grip the back of the arm, and receive a nut and plate to secure the paddles.

Paddle wheels are sometimes provided with cast iron floats to act as counterweights to some unbalanced part of the engine. They are mostly required on side lever engines having a single crank; they are placed nearly opposite to the crank, but not quite, so that they may prevent it from stopping on the centre, and be difficult to start again.

Paddle wheels for engines having a single crank sometimes have their floats of varying breadths, so as to keep the speed of revolution as uniform as possible. This is accomplished by making some of the floats wider than the others. The broadest floatsare in action when the crank is at its points of greatest power, and the narrowest at the time the engine is on a dead centre, hence there are four general graduations of breadth in the circumference of the wheel.

A radial paddle wheel is one in which the floats are fixed to the paddle arms, and their ends are in a line radiating from the centre of the paddle shaft.

A feathering paddle float is pivoted at the centre of its ends, and so arranged that by a mechanical movement it will remain vertical when in the water, notwithstanding the circular path it revolves in.

The object of feathering is to cause the thrust of the float to be as nearly as possible in a horizontal line, and therefore more nearly parallel to the line of the ship’s motion, and thus utilize more of the paddle power to drive the ship.

The eccentric for feathering the floats is fixed to the ship’s side, and sometimes carries a plummer block or pillow block for the paddle shaft bearing. The centre of the eccentric sheave or wheel is placed ahead of and level with the paddle shaft axis. The working surfaces of a feathering wheel are of brass, and the bushes of the paddle arms of lignum vitæ.

The surfaces are lubricated by the water, but sometimes oil lubrication is provided for the eccentric sheave.

A disconnecting paddle engine is one in which the paddles may be driven separately or together. This is effected at the inner port bearing by a clutch wheel, which slides endways on the shaft and is driven by feathers seated in the shaft. This clutch wheel is operated by a lever so as to engage or disengage with the crank pin, which is fast in the outer crank.

Disconnecting paddle engines are always fitted with loose eccentrics, such engines being used for steam tugs and ferry boats, where quickness of turning and of reversing is of great importance.

The thread of a screw propeller is its length measured along the outer edge of the blade.

The angle of the thread is its angle to the axial line of the propeller shaft.

The length of the thread is the length of the outer or circumferential edge of the blade.

The area is the surface of one side of the blade.

The diameter is the distance apart of the two points on the edges that are diametrically opposite and furthest apart.

The pitch of a propeller is its degree of spirality, and is represented by the distance it would move forward if the water was a solid. It is measured by drawing a line representing the axis of the propeller shaft, and at a right angle to it a line representing in its length the circumference of the circle described by the tips of the blades; from the point of intersection of these two right angle lines a diagonal line is drawn representing the angle the blade at its outer edge stands at the propeller shaft axis. The greatest distance between the diagonal line and the line representing the propeller circumference is the pitch of the propeller.

A left handed propeller has a left hand thread or spiral, and revolves from left to right to move the ship ahead.

A right hand propeller has its blades inclined in the opposite direction, and of course revolves in the opposite direction to a left hand one.

The slip of a propeller is the difference between the distance the ship is moved by the propeller and the distance it would move if the water was solid. Slip is usually expressed in the percentage that the distance the ship actually travels bears to the distance she would have travelled if there had been no slip. From 10 to 20 per cent. is lost in slip.

A screw of increasing pitch is one in which the angle of the face of the propeller blade to the axis of the shaft increases as the thread recedes from the shaft, or from the centre to the circumference of the blade, or in both directions.

In a uniform pitch the angle of the blade to the propeller axis is the same at all distances from the axis.

An example of a screw of uniform pitch would be a piece of angle iron wound around a parallel shaft. If wound on a tape shaft, the largest diameter being nearest to the ship’s stern, it would have an increasing pitch. If wound around a parabola, the pitch would vary at every point in its diameter and thread.

A thrust bearing is a journal bearing provided with a number of corrugations or collars fitting with corresponding corrugations or recesses in the thrust block, the area thus provided serving to resist the end thrust placed by the propeller upon the shaft.

It must be freely lubricated by ways leading to each collar or corrugation, and so situated that it is accessible for examination. It is sometimes at the end of the first length of shaft aft of the engine.

A stern tube is a sleeve enveloping the aft end of the propeller shaft to protect it from the sea water, which would corrode it. At the aft end of the stern tube is a gland and stuffing box. At the inner end, which extends to the aft bulkhead, it has a flange which is bolted to the bulkhead.

The bearing area of the shaft and stern tube are lined with brass (about half an inch thick) to prevent their oxidation from the action of the sea water.

A lignum vitæ bearing is a wooden bearing generally fitted to the outer end of the stern tube in propeller engines, or to the outer ends of the paddle shaft of paddle engines. It consists of strips of lignum vitæ dovetailed into the bearing or bush, and running lengthways of it. These strips are prevented from working out by a check plate at each end of the bearing.

Screw propellers may be fastened to their shafts in several ways, as by a key or feather sunk in the shaft, and projecting into a keyway in the propeller bore, and a nut on the end of the shaft with a safety pin outside the nut, or by a key passing through the boss of the propeller, and a safety pin or plate upon the key.

The principal pipes of a marine engine and boiler, and the parts they connect, are, the main steam pipe, connecting the stop valve on the superheater to the steam chest of the engine cylinders; the waste steam pipe from the safety valve to the open air; the blow-off pipe, connecting the blow-off cocks on the bottom of the boiler with the blow-off Kingston cock on the ship’s side; cylinder jacket pipe from the stop cock on the boiler to the steam jacket.

The circulating suction pipe, connecting the main Kingston valve with the bottom of the circulating pump; the circulating delivery pipe, connecting the discharge compartment of the condenser with the main delivery valve on the ship’s skin; the air pump suction, connecting the body of the condenser with the suction side or bottom of the air pump; the main exhaust pipe, connecting the exhaust passage of the low pressure cylinder with the condenser; the feed water suction pipe, connecting the donkey feed pipe with the hot well; the feed water delivery pipe, connecting the donkey feed pump with the check valve on the boiler; the bilge suction pipe, connecting a strum box in the bilge with the bilge pump; a suction pipe from the strum in the bilge to the donkey pump; the bilge pump delivery pipe, connecting the bilge pumps with bilge delivery valves on the ship’s side.

A mud box is a rectangular box usually placed in the engine room, and serving to clear the bilge water from foreign substances, as small pieces of wood, coal, etc.; the construction is as follows: It is on the suction side of the bilge pumps, and is provided with a hinged lid that affords access to clean it out, and that must obviously close air tight, or the bilge pumps will not draw. The box is divided into two compartments by a loose division plate that stands vertical, and is perforated so as to act as a strainer.

The steam from the boiler passes through the superheater, main stop cock or valve, main steam pipe, separator, regulating and throttle valve, steam chest, steam port, steam passage into cylinder, returns through steam passage and port, exhaust cavity of valve into either the condenser or the low pressure cylinder, as the case may be, finally exhausting into condenser, whence the water of condensation is pumped by the air pump into the hot well. In the case of a jet condenser part only of the condensed steam goes back to the boiler, the rest going into the sea through the injection discharge pipe.

A steam jacket[61]is an outer casing to a steam cylinder, the space between it and the cylinder being filled with steam direct from the boiler, with the object of preventing condensation of the steam in the engine cylinder.

[61]Seepage 374on steam jackets.

A drain cock is supplied to the bottom of the jacket to pass off condensed water. Steam jackets should be lagged or felted to prevent condensation.

The parts of an engine that require to be felted or lagged are the cylinders and the steam pipes; the boilers also should be felted or otherwise covered to prevent loss of heat by radiation, and the uptake protected by means of thin plates, kept, by means of distance pieces and bolts, at a distance of two or three inches from the plates of the uptake.

Various non conducting substances are employed to prevent radiation, as, for example, felt, mineral wool, asbestos, and various kinds of cement.

The pieces of the engine through which the steam pressure is received and transmitted are as follows:

The piston, piston rod, cross head, cross head gudgeon, connecting rod, crank pin, crank shaft and couplings to the propeller shaft.

Trunk engines are generally used in war vessels where it is required to have the engines below the water line. The trunk passes through the cylinder and the piston is upon the trunk, the connecting rod passes down into the trunk and connects direct to the piston. A stuffing box and gland in each cylinder cover keeps the trunk steam tight. The trunk forms a guide to the piston in place of the ordinary cross head and guides, and thus saves the room required by those parts.

The cylinders for a right handed propeller should be on the starboard side of the vessel, so that the pressure on the piston, when the engine is going ahead, shall be in a direction to lift the trunk in the cylinder, and thus act to relieve the gland and cylinder bore of the weight of the trunk and piston.

An oscillating engine is one in which the cylinder is mounted on bearings called trunnions, so that the cylinder can swing and keep its bore and the piston pointing to the crank at all parts of the engine revolution. This enables the connecting rod and slide bars to be dispensed with. The trunnions are hollow, one containing the steam and the other the exhaust passage.

Oscillating engines are used for paddle steamers, because their construction permits of a good length of piston stroke, while still keeping the engine low down in the vessel.

The valve motion for an oscillating engine consists of an ordinary eccentric gear or motion, with the addition of various mechanical arrangements to accommodate the valve gear to the vibrating motion of the valve chest.

The stuffing box of an oscillating engine is made deeper than usual because the gland bore has more strain on it, and extra wearing surface is therefore required to prevent its wearing oval.

Geared engines are those with gear wheels to increase the revolutions of the shaft above those of the engine, and thus obtain a high propeller speed without a high piston speed.

The pressure that propels a vessel is taken by the thrust block in a screw propeller engine.

The pressure that drives a paddle steamer is applied to the hull at the shaft bearings and their holding beams, and to the bed plates. The amount of fuel required per horse power per hour, by modern compound engines, is from about 11⁄2to 3 lbs., and by common condensing engines from 3 to 5 lbs. per horse power per hour.

The unit or measure of a horse power is the amount of power required to lift 33,000 lbs. one foot high in a minute.[62]

[62]Seepage 407, Vol. II.

Nominal horse power is a term used to represent the commercial rating or power of an engine, and is usually based upon the area of the piston. It gives no measure of the engine power, however, because it does not take the piston speed into account.[63]

[63]Seepage 374, Vol. II.

In a surface condensing engine the duty of the air pump is to merely pump the condensed steam and vapor from the condenser to the hot well, whereas in a jet condensing engine it has to also take the condensing water from the condenser, hence an air pump for a surface condenser may be made smaller than that for a jet condenser. As the air pump works against the pressure of the atmosphere, therefore the smaller it is the less of the engine power is absorbed in working it.

The injection cocks are regulated for opening by rods having handles attached. If the injection cocks are not open wide enough, the condenser will get hot and impair the vacuum, while if opened too wide, the water in the hot well will be cold and the boiler feed will be cold. These cocks should be so regulated as to keep the temperature in the hot well at about 100° Fahrenheit.

The parts of a marine engine that are exposed to danger in a cold climate are all pipes through which cold water circulates, and are liable to freeze.

The precautions necessary to prevent freezing in cold climates are to cover all pipes liable to freeze, to keep the water circulating through them, or to let it out of them if necessary, as in the case of the engine standing.

A marine engine may fail to start, or may be prevented from starting by the following causes:

1st. The H. P. slide valve may be off, or away from its seat, thus admitting the steam to both sides of the piston at the same time.

2d. The engineer may have forgotten to disengage the hand turning gear from the crank shaft.

3d. The propeller may be fouled with a piece of timber, or by a chain or rope (these causes sometimes occurring when the ship is in port), or there may be something wrong with the outer bearing of the propeller shaft.

4th. In the case of a propeller fitted with a banjo frame (for the purpose of raising the propeller) the propeller may be locked.

5th. An obstruction, as a block of wood, in the crank pit may prevent the crank from turning.

6th. The slide valve nut may have slackened back, thus loosening the slide valve.

7th. The slide valve spindle may have broken.

8th. When an engine has no auxiliary or starting, but animpulsevalve that merely lets a puff of steam into the receiver, this impulse valve may leak, and if the escape or relief valve on the receiver is too much loaded, it may gag the H. P. piston by giving it high pressure steam on both sides, and this may throw the valve off its seat. Similarly, if the engine has an auxiliary or starting valve, and it leaks, high pressure steam may be admitted to both sides of the L. P. piston, thus gagging it and causing its slide valve to throw back and away from its seat.

9th. The cylinders may be choked with water, and the drain cocks choked up.

10th. The crank shaft bearings may be screwed up too tightly.

11th. The air or the circulating pump may be choked with water, either the air pump overflow valve or the circulating discharge valve being secured down.[64]

[64]The air pump overflow valve should never be permanently fastened down. More engines have been broken down from this than from almost any other neglectful cause, because, from great leaks in the condenser tubes and engines standing for a length of time, a larger quantity of water may require to be got rid of during the first few strokes of the pump than can pass through the small air or vapor pipe, which is usually fitted from the hot well either into the bilge or else overboard. Unless the valve in this overflow pipe is heavy enough of itself (which is very rarely the case), it should be loaded by a spring or weight, so that when the puff of the air pump causes it to lift, and the vessel is rolling, sea water may not pass into the hot well. To avoid this, some engineers erroneously fasten this valve down. An experienced engineer states that in his experience five engines have been broken down from this cause alone.

12th. From the engines being allowed to stand a long time in one position, and the glands being too tightly packed. An engine should be turned a little daily when not in use.

13th. From the piston rings being set out too tight to the cylinder bore.

14th. From the throttle or stop valve being shut, as from its spindle being broken.

15th. From the eccentric sheave, or wheel, having shifted on the shaft, some eccentrics having a key that is not sunk in the sheave, which is done so that the eccentric may shift rather than break if it should seize in its strap.

16th. From the H. P. piston leaking badly, or its ring beingbroken, which will permit the cylinder to fill with steam and the slide valve to unseat.

17th. If the engine has been overhauled, the forward eccentric may have been connected to the wrong end of the link, thus giving an improper motion to the slide valve.

18th. The expansion may be set to cut off too early in the stroke.

19th. From the air pump rod, or from the circulating pump rod being broken, or from the valves being broken.

20th. From the cylinder casing or the receiver being cracked so as to admit steam to both sides of the piston at the same time.

A defective vacuum, or loss of vacuum, may occur from the following causes:

1st. From the glands of the low pressure cylinder leaking.

2d. From the pet cock of the air pump being left open.

3d. From the joints of the connections about the condenser leaking.[65]

[65]To discover a leak about a condenser, pass an exposed light, as a candle, about the joints, etc., and where there is a leak the flame will be drawn in towards the condenser.

4th. From the condenser being cracked, and therefore leaky.

5th. From the injection cock or valve being closed.

6th. From the condenser tubes being foul for lack of being cleaned. From the L. P. cylinder escape valves or cylinder cocks being leaky, and therefore letting in air.

7th. From the slide valve and piston of the L. P. cylinder leaking.

8th. From the air pump valve being leaky or broken. From the circulating pump being defective, as from having leaky valves.

9th. From the Kingston injection valve not being properly opened, or from its outside orifice being choked.

10th. The bilge injection may be so connected with the air pump or condenser as to impair the vacuum when its valve is accidentally stuck and its stop cock is left open.[66]

[66]It is obvious that a defective vacuum may or may not prevent an engine from starting, according to the degree of defectiveness.

The principal causes of heating are:

1st. The bearing caps being screwed down too tight.

2d. The bearings being left uncovered, thus allowing the brick dust used for cleaning the machinery, the dirt from coaling the ship, or the sand used for cleaning the decks, to get into the bearing.

3d. The oil grooves in the brasses being worn out or too shallow, or the brasses not being cleared at the sides.

4th. Improper fitting of the distance pieces or fit strips between the brasses.

5th. Bad oil or too light an oil.

6th. If the brasses are too slack and thump or pound, the back of the brass may be stretched by pening, causing the sides of the brass to close in upon and bind the crank journal or crank pin, and this will cause heating.

For other information concerning the engine see as follows:

Largeimage(288 kB).Fig. 3405Fig. 3405.

Largeimage(288 kB).

Fig. 3405.

Figs. 3405and3406represent a triple expansion marine engine, the construction being as follows:

Back to Index Next