IMPROVEMENTS IN BALANCED SLIDE VALVES FOR STEAM ENGINES
Year: 1882

page_text: PROVISIONAL SPECIFICATION left by Alexander Melville Clark at the
Office of the Commissioners of Patents on the 2nd August 1882. Communi-
cated to him from abroad by John James De Lancey, of Binghaunton, in the
County of Broome and State of New York, United States of America.
ALEXANDER MELVILLE CLARK of the firm of A M and W Clark of 53, Chancery
Lane, in the County of Middlesex, Patent Agents. IMPROVEMENTS IN BALANCED
SLIDE VALVES FOR STEAM ENGINES Communicated to him from abroad by John
James De Lancey, of Binghamton, in the County of Broome and State of New
York, United States of America
This invention relates to that class of slide valves that are fitted to work
beneath the face plate in the steam chest, and consists in certain features of con-
struction and arrangement, whereby the operation of the valve is rendered more
effective, and excessive wear prevented.
The valve is made hollow, of rectangular form and with perpendicular faces, on
both its inner and its outer sides. The face plate fits in the steam chest above
the valve, and a slotted balance plate upon the valve and beneath the face plate.
The upper edges of the valve are formed with longitudinal grooves to receive
packing bars which are connected at each corner by square lap joints, so that the
longer side bars support the shorter end bars, and beneath these packing bars are
plate springs that act to press the packings outward. The springs are preferably
of elliptical form, and may have their bearings on the ends of the bars or on a
flattened surface at the mid-length of the bar, The ends of these springs have
slots which work on safety pins in the corners of the valves. These pins enter
holes in the ends of the long bars to prevent the escape of any part of the spring
if it should break. The two long springs are all that is required to keep the
packing up; the two shorter ones are used simply for safety in case the longer
springs break.
The packing bars are made square in cross section, so that the
steam shall have equal surfaces to act upon at each side, and so that the springs
will operate the same under pressure, as they will without the pressure on the seat
or face plate that is worn out of surface. In the sides of the valve are apertures
for admission of steam beneath the packing bars. The balance plate is in steam.
tight contact with the packing bars and with the face plate above, and is formed
ID 477

page_text: with flanges on its under side that fit loosely within the valve and this plate is of
such size, that its outer edges are on a line, or nearly so, with the outer edges of
the packing bars but, if more friction is desired, this plate may project over the
edges of the packing bars. The upper surface of the balance plate is formed with
longitudinal and transverse oil grooves, and the surface of such grooves is made to
equal that of the packing bars beneath the plate, the object being to ensure the
exact balance of the plate under any steam pressure, and to prevent friction
between the balance plate and the face plate, except what may be due to the
upward pressure of the springs on the packing bars.
The face plate fits closely in the steam chest, with the exceptions of openings
that are provided to allow free circulation of steam in the chest. The plate is
supported by rests that are cast upon its under side and take upon the valve seat
or bottom of the chest, or the rests may be supported by lugs cast upon the inner
surface of the chest. Set screws in the steam chest cover, serve to hold the face
plate down. When the valve wears or is faced down, the face plate is corre-
spondingly adjusted by reducing the length of the rests. For oiling the valve, a
recess is formed in the upper surface of the face plate, and a small aperture is
made through the plate at its centre, and beneath an oil cup in the steam chest
cover. The oil will pass through the opening to the oil grooves in the balance
plate and by the grooves be distributed over the contact surfaces. The object in
constructing the valve with perpendicular faces, is to allow the removal of all
pressure on the valve except what is necessary to keep it down on its seat when
the port is covered, and the cylinder full of steam. The square form of the packing
bars, facilitates the movement of the packing up and down by the springs in cases
where the valve seats and face plates are worn unequally; with packings having
less face than depth, the pressure of the face plate which holds them downward
being upon the narrowed face, and the steam pressure upon the widest face, they
may be held down by the steam pressure instead of rising to the hollows in the
face plate. By the use of the rests cast with the face plate the adjustment of the
plate to the valve is much facilitated, as the rests have simply to be planed off
to correspond with the reduction in the depth of the valve.
It will be understood that the balance plate moves with the valve, the object
being to obtain a broader wearing surface without increase of pressure. There is
no pressure on the balance plate, except what is given to it by the packing bars,
and if that is found to be excessive, it can be reduced by increasing the exposed
surfaces of the oil grooves, but in no case, should the surface of the oil grooves, be
greater than the surface of the packing. These oil grooves ensure complete
lubrication, of the friction surfaces. The slots in the balance plate are to allow the
escape of steam to the exhaust cavity in case the facings become worn sufficiently
to allow the steam to blow through. Further, by using this balance plate the
packings are entirely preserved from wear, so that when once fitted it will not be
necessary to remove them. By constructing the sides and ends of the valves with
plane, perpendicular surfaces, instead of the usual projecting flanges, a larger
exhaust cavity may be obtained and all downward pressure upon the valve is
prevented.
In a modified construction the separate balance plate is dispensed with and the
face or balance plate bears directly upon the packing of the valve. The valve is
formed on its upper side with transverse ribs so as to obviate all pressure on the
valve with the exception of that required to maintain a steam tight contact with
the valve seat. On the outside and centre of each bar there is a projecting lug.
which works in a slot made in the inside of the packing groove.
These lugs carry
the bar independently of the joint at the corners, thereby preventing the bar from
changing its relative position, with the face plate, and obviating the usual wear at
the points of contact. The face plate has its bearing on four projecting lugs upon
the inside of the steam chest, and takes the pressure off the valve, by which means
the usual attachment to the steam chest cover is obviated, and a more satisfactory
adjustment secured. Between these lugs and face plate are four bars which have

page_text: projections from the top and centre, entering notches, in the face plate which hold
them securely in position. When the valve is faced down, the face plate is
adjusted to its position upon the valve by reducing the thickness of the bars and
the screws of the chest cover are to be turned down to correspond. For oiling the
valve a recess is made in the face plate directly under the oil cup, and from this
recess oil passes through channels to oil holes in each of the four sides of the face
plate so that it is distributed over the large packing bars, when the valve is at its
extreme travel, and over the short bars without intermission. In place of screws
in the chest cover, for holding the face plate down, the plate may be fitted with a
pocket in which are spiral springs that take against the chest cover.