IMPROVEMENTS IN STEAM ENGINES, AND IN OBTAINING FEED WATER FOR MARINE STEAM ENGINE BOILERS
Year: 1860

page_text: PROVISIONAL SPECIFICATION left by David Mardell at the Office of
the Commissioners of Patents, with his Petition, on the 28th November
1860.'
I, DAVID MARDELL, of York Terrace, York Square, Commercial Road
East, in the County of Middlesex, Engineer, do hereby declare the nature of
the said Invention for "IMPROVEMENTS IN STEAM ENGINES, AND IN OBTAINING
FEED WATER FOR MARINE STEAM ENGINE BOILERS," to be as follows:-
My Invention relates to an arrangement of parts of steam engines in which
the high-pressure steam, before being admitted to the large or expanding
cylinder is first admitted to one of two high-pressure cylinders, these three-
cylinders being so combined and arranged that the large or expanding cylinder
makes two strokes for each stroke of either of the high-pressure-cylinders..
which may be readily effected by coupling the crank shaft of the high-pressure-
cylinders with the crank shaft of the low-pressure cylinder, by means of wheel
gearing, or otherwise; I place these three cylinders in close proximity to each
other, and form passages direct from the high-pressure cylinders to the expan-
sive cylinder, so that the steam finds immediate ingress to the large cylinder
from either of the smaller ones, and without the necessity of passing through
the steam ports of the small cylinders or their valves. The high-pressure
steam is controlled in its admission to and escape from the high-pressure cylin-
ders by slide valves in the ordinary manner, which also regulates its escape to
the condenser after having operated (as before mentioned) in the low-pressure
or expanding.cylinder. The ordinary action of slide valves cutting off at the

page_text: up stroke, (for example), say at about three-quarter stroke of the piston,.
suffices for the proper admission and escape from the high-pressure cylinders
as during the remaining third part of the stroke of high-pressure cylinder the
steam will pass from that cylinder and expand in the low-pressure cylinder.
throughout two-thirds of the up stroke of its piston. The remaining third part
of the stroke of this piston is performed while one-sixth part of the down-stroke
of high-pressure piston is being performed. Supposing the expansion of steam
to have been carried to its extreme limit, the slide valve of high-pressure
cylinder now opens to the condenser, and exhausts both the high-pressure and
low-pressure cylinders below their pistons. The high-pressure steam is at
same time taking effect above the piston of the high-pressure cylinder before
mentioned, and which having completed about three-quarters of its down stroke
is also admitted below the piston of the condensing cylinder, when a like action
is repeated. The second high-pressure cylinder works in like relation to the
condensing cylinder, but passes its steam both from above and below its piston
to the low-pressure cylinder above its piston, expanding in and escaping from
it in manner similar to that before described. With reference to the first
described high-pressure cylinder, I establish communication between the high-
pressure cylinders and the low-pressure condensing cylinder by forming two
sets of numerous small passages through the high-pressure cylinder; each set
being disposed at a distance from the ends of the cylinder of about one-third of
its length. These two sets of openings in the one high-pressure cylinder enter
a passage leading to the bottom of the low-pressure cylinder, and in the other
high-pressure cylinder to a passage leading to the top of the low-pressuro
cylinder, which constitutes its only steam ports. The two series of small-
through passages in each of the high-pressure cylinders open into one and the
same channel; the whole are of such ample area as to afford the greatest
facility for the passage of the steam. The escape of the steam from the high-
pressure cylinders to the low-pressure cylinder is effected by their pistons
passing the series of openings or ports last herein-above mentioned; but the
two series are further regulated in their passage by valves which are so actuated
and controlled that during the up stroke of the high-pressure pistons the lower
series of openings are closed, and during the down stroke the upper series are
closed. This regulation of the passages permits of the high-pressure steam
operating at full pressure during two-thirds of the stroke, and permits also of
its passage into the low-pressure cylinder during its complete stroke.
It also permits of the escape of the steam to the condenser from the low-
pressure cylinder until it completes its stroke in either direction. By this
arrangement of engine I obtain a vacuum in the low-pressure cylinder during

page_text: the whole length of the stroke and in the high-pressure cylinders through-
out nearly the whole length of their strokes. Instead of exhausting the low-
pressure cylinder through the high-pressure cylinders, I sometimes form that
cylinder with exhaust ports and valve of its own leading to the condenser, and
thereby exhaust direct; this exhaustion will also exhaust the high-pressure
cylinders at same time. My improvements further consist in obtaining fresh
water from salt water, for the purpose of supplying the boilers of marine
engines. In order to effect this, I admit the salt water into a closed vessel to
which heat is applied; I at same time apply a pump to exhaust the area
of this vessel above the water, and maintain therein a partial vacuum. By
this means a thick vapour rises from the salt water, which is carried away by
the pump and delivered into a vessel, wherein it condenses, being fresh water.
This water is afterwards forced into the boiler by a pump in the usual
manner.