Three-cyl′in-der En′gine.
An arrangement of three cylinders working on a common crank-shaft, to overcome the dead-center without a fly-wheel.
The eccentrics and valves are so set that steam is admitted to the cylinders in succession, and not simultaneously, by which means the pistons are always in different thirds of their stroke, and two cylinders are always acting effectively.
In the drawing (
Fig. 6412), the piston in the upper cylinder is at the outboard end, the one at the left at one third of the inboard stroke, and the one on the right at two thirds of the outboard end and exhausting.
Brotherhood's engine (
Fig. 6413) has three connected cylinders
a b c at angles of 120° to each other.
Each has a deep but light piston connected to a crank
d, common to all. One of the connecting-rods has a single eye at the crank end, while the other two are forked at that end, one straddling the other, so that their centers are in the same line.
Steam is admitted into the central space
g through the induction-opening
e, and exhausted through the opening
f in line with the crank-shaft.
The supply and exhaust are effected by a revolving slide-valve carried around by the crank-shaft.
The steam-pressure in the central chamber always exceeds that on the outer end of each
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piston, but varies in amount, so that the strain on the connecting-rods and joints is always in one direction, permitting the engine to be run at very high rates of speed.
The direction of motion in the example is shown by the arrow.
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Machine for winding button-hole twist. |
Many marine and river engines have three cylinders, and some have two acting at angles of 120° and an air-pump occupying the position of a third steam-cylinder.
A favorite arrangement with
Maudslay and
Penn.
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Machine for producing variegated thread. |
The
Baxter canal steam-engine has a pair of high-pressure cylinders and a lowerpressure cylinder between the other two.
In Willans's threecylinder engine (Fig.
6414), each cylinder is single-acting, receiving its steam upon the upper side only of the piston.
The connecting-rods attached directly to the pistons actuate a three-throw crank-shaft.
Each piston serves as a steam-valve controlling the supply of steam to one or the other of the two remaining cylinders There is a steamchamber in each piston and a port in its side.
Steam is supplied by means of a hollow rod passing through the top of the cylinder into a steamchest.
When the piston attains three fourths of its downward stroke, its steam-port overlaps a port in the side of its cylinder and steam then passes to the top of another of the cylinders.
When the piston has reached about one half its return stroke, uncovering the port in the side of its cylinder, it allows the steam to escape from the cylinder into which it was previously ad mitted, into a casing round the crankshaft, from which the exhaust-steam is taken either to a condenser or to the air, as the case may be.
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Thread-winding guide. |
In an engine which is required to run only one way round, the port in the side of each cylinder passes direct to the top of one of the other cylinders; but where it is desired to reverse the engine, as in the one illustrated, the ports to the top and those to the sides of each cylinder meet in a three-way cock, which, connecting the port on the side of any one cylinder with that to the top of either one or the other of the other cylinders, reverses the engine.
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Three-box loom. |
The equilibrium of the power is maintained by its threefold action.
The lubrication is done through a steam-lubricator on the steam-chest, and the waste oil passing down to the bottom of the casing lubricates the lower ends of the connecting-rods as they pass round.
