IMPROVE- MENTS IN APPLIANCES FOR ACTUATING RAILWAY BRAKES
Year: 1881

page_text: PROVISIONAL SPECIFICATION left by John McLeownan McMurtrie and
Hugh Smellie at the Office of the Commissioners of Patents on the 17th
November 1881.
JOHN MCLEOWNAN MCMURTRIE, of Glasgow, in the County of Lanark, and
HUGH SMELLIE, of Kilmarnock, in the County of Ayr, North Britain. " IMPROVE-
MENTS IN APPLIANCES FOR ACTUATING RAILWAY BRAKES."
This Invention relates to certain improvements in appliances for actuating
railway brakes, whereby the power of applying or taking off the brakes may be
regulated or controlled in a more effective and reliable manner than hitherto.
The Invention comprises a new combination of appliances consisting of an
ordinary cylinder and piston connected by the piston rod and levers to the brako
block, and a new regulating valve operated by the driver or other attendant, and
through which steam or compressed air is admitted to and exhausted from the
cylinder. The cylinder is by preference arranged so that the piston rod passes
downwards and is connected below to a lever actuating the brake block, and so
that the brake is applied by the upward motion of the piston. Steam which may
be led by a pipe direct from the boiler is admitted freely under the piston, and
when the brake is to be off, steam of equal pressure is admitted through the
regulating valve referred to above the piston. The steam above however acts on
the full area of the piston, whereas that below acts an area which is less than the
area of the piston by the extent of area of cross section of the piston rod working
out through the cylinder, and thus apart from the weight of the piston and
connecting parts, the pistón will, when an equal pressure of steam is maintained
on both sides, be kept at the lower end of the cylinder to keep off the brake.
When it is desired to apply the brake, the admission of steam above the piston is
shut off by means of the regulating valve, to be hereinafter described, and the same
action of the valve is made to exhaust a portion of the steam above the piston,
until by the remaining steam expanding, the pressure is reduced to such an extent
on that side of the piston that it is immediately forced up by the steam of full
pressure underneath and the brake is applied. The power of applying the brake is
thus determined by the extent to which the pressure above the piston is reduced,
and which can always be made apparent to the driver or brakesman on the engine
by means of a pressure guage.

page_text: The valve which regulates the admission to and exhaust or eduction of steam
from the cylinder is fitted at any position on the engine convenient for the driver
or brakesman, and consists of a valve chamber to which steam from the boiler is
admitted freely, and having formed in the valve face which is circular two separate
ports, which coinmunicate, the one with a steam pipe leading to the upper end of
the brake cylinder and the other to a pipe forming a means of exhaust to the
atmosphere, the latter port being in the centre and the other excentric. The valve
which lies flat on the valve face is by preference circular plate, and has an inlet or
admission port cut through it in the form of a segmental slot at such a distance
from the centre as to come over the excentric port on the valve face for the
admission of steam to the cylinder, while as an exhaust port a recess is formed in
the face of the valve which extends from the centre outwards as far as the excentric
port. The valve is carried on a central spindle which passes out by a stuffing box
from the valve chamber, and is fitted with an operating handle or lever outside, by
which the valve is turned or ocillatted to bring the inlet port over the corresponding
port on the valve face for the admission of steam, and to bring the exhaust port or
recess in the valve over both the eccentric and central ports in the valve face for
the eduction or exhaust, whether partial or complete, of the steam from the upper
end of the brake cylinder.