24

THE COLLIERY GUARDIAN.

January 1, 1915.

THE “MARSHALL” DROP VALVE
ENGINE.

The accompanying photograph (fig. 1) shows a pair
of large tandem compound engines, coupled, which
have been supplied by Messrs. Marshall, Sons and Co.
Limited, of Gainsborough, for the Tinsley mills of
Messrs. Wm. Cooke and Co. Limited, of Sheffield, with
the following dimensions:—High-pressure cylinders,

of each for each end of the cylinder, with suitable
operating mechanism driven from the lay shaft M,
which is geared to the engine crank shaft by mitre
wheels with machine-cut teeth. The steam admission
valves are lifted alternately by levers B, which are
depn ssed at their outer end by the bell crank levers 0.
Motion is given to the bell cranks by eccentrics E,which
reciprocate the side links D, carrying the bell cranks on
pivots. A stop is provided, so that the bell crank, which
is counter-weighted by its inner arm, occupies the

work of disengaging does not thereby re-act on the
governor. Immediately disengagement is complete, the
valves close smartly and quickly under the influence
of the helical springs and the air cushion in the spring
boxes L. Air valves regulate the actual closing speed
and prevent undue pounding and wear between the
valves and seats. All the working parts of this gear
are case-hardened, and the tripping edges are made of
specially hardened material

The exhaust valves are operated by eccentrics on the

1

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r

i j

■

■,L ' ■ ■	• >

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Fig. 1—Set of 20 in. and 35iiN. by 48 in. Stroke Coupled Tandem Compound Engines of 1,850-H.P.
Supplied for the Rod Mills at the Tinsley Works of Messrs. Wm. Ccoke & Co. Ltd., Sheffield.









Aq,

lai

Fig. 2.— ‘Marshall” Patent Trip Gear.



20 in.; low-pressure cylinders, 35j in.; stroke of piston,
48 in. The engine is capable of developing at the most
economical load about 1,120 indicated horse power when
running at 80 revolutions per minute, steam pressure at
stop valve on engine at 140 lb. and cut-off at 25 per
cent, of stroke. With the cut-off at 50 per cent, of the
stroke, the maximum power would be about 1,850
indicated horse-power.

This engine is fitted with the “ Marshall ” patent trip
gear, shown in fig. 2. The gear consists of equilibrium
double-beat steam valves A and exhaust valves N, one

correct position for engaging with the lifting lever B.
The amount of engagement is constant, and the period
of engagement is determined by the governor which is
connected toshaft J. This shaft carries the eccentiics H,
which vary the position of the trip pads G. The travel
of the eccentric E brings the inner arms F of the bell
crank levers C into contact with the trip pads G, and
the further movement compels disengagement between
lifting levers B and bell cranks C.

It will be noticed that the pressure of F on the trip
pad G has little or no tendency to rotate shaft J. The

lay shaft. The lower end of the exhaust eccentric rod
is connected to lever O pivoted at P. ') he lever Q
pivoted at R is extended past the valve spindles, and
rests on circular bosses of lever O when the valve is
seated. The valve spindle is extended below the lever
attachment and connected to a spring S, which ensures
the connection between the upper side of lever Q and
pad T, and preserves a perfectly regular and silent
motion. The upper side of lever O is curved to
accelerate the rate of valve opening and give a free
exhaust.