IMPROVEMENTS IN MECHANICAL RELAY APPARATUS TO BE USED IN CONNECTION WITH GOVERNING, REGULATING, STARTING, STEERING AND ANALOGOUS APPARATUS
Year: 1883

page_text: PROVISIONAL SPECIFICATION left by David John Dunlop at the Office of
the Commissioners of Patents on the 24th February 1883.
DAVID JOHN DUNLOP, of Port Glasgow, in the County of Renfrew, North
Britain, Engineer and Shipbuilder, "IMPROVEMENTS IN MECHANICAL RELAY
APPARATUS TO BE USED IN CONNECTION WITH GOVERNING, REGULATING, STARTING,
STEERING AND ANALOGOUS APPARATUS "
This Invention has for its object to simplify and otherwise improve mechanical
relay apparatus and to advantageously apply the same in connection with
governing, regulating, starting, steering, and analogous apparatus. In connection
with electrical apparatus the term "relay" is applied to a device operated by one
current which may be a comparatively weak one so as to set in action another
current which may be a comparatively strong one; and in applying the same term
to mechanical apparatus a kind is intended to be designated in which a com-
paratively weak force acting to a certain extent is made to cause a comparatively
strong force to act to a corresponding extent.
One important application of the present Invention is intended to be made in
connection with governing apparatus for screw-propeller engines, and of the kind
described in the Specification of Letters Patent obtained by the present applicant
and dated 30 March 1871. (N° 852) In the governing apparatus referred to a
varying pressure caused in apparatus at the stern of the ship by the varying
immersion of the stern is transmitted to the engine room and there made to operate
on the throttle valve of the engines. When arranged to act directly on the
throttle valve of the main engines the governing apparatus has to be proportioned
to suit the power required to move the throttle valve; and when the engines are
large or the throttle or regulating valve of a kind requiring extra power the
apparatus becomes cumbersome. By the present Invention however the primary
governing apparatus may be kept comparatively small whatever may be the power
required to move the throttle valve. The most important peculiarity of the
Invention, however, consists in a device whereby the greater force brought into
action by the relay apparatus, is made to act to an extent corresponding precisely
to the extent of movement of the primary apparatus.

page_text: In carrying out the Invention in connection with the governor herein before
referred to or any other suitable governor according to one modification, a cylinder
with a piston is employed to move the main throttle valve, and is actuated by
steam or other elastic fluid or by water or other liquid under pressure, the action
being controlled by a small slide or other valve moved by the primary governing
apparatus. When an ordinary slide valve is used a plate is interposed between it
and the cylinder port face and has passages formed through it to communicate with
the cylinder passages and with the exhaust port. The plate has a rod fixed to it
which passes out through a stuffing box and is externally connected to the piston
rod either directly or through a lever so as to move with the piston at the same
rate or at a proportional but reduced rate. The ports on the outer side of the
plate are narrow but the passage ports on the cylinder port face or those on the
inner side of the plate or both are enlarged so that the cylinder passages and those
in the plate may keep in communication notwithstanding the movements of the
plate. If the valve is in a middle position relatively to the plate, the plate and
piston being in any position, then on the valve being moved in either direction
steam will get access to move the piston in the same direction but the plate will
also move correspondingly and by carrying the port under the valve will stop the
admission of steam as soon as the piston will have moved to an extent precisely
corresponding to the extent of movement of the valve whether that extent be
small or great. Should the steam admitted before the closing of the port produce
further movement of the piston by its expansive action such further movement
will immediately uncover the port to the exhaust cavity and thus render any still
further expansive action ineffective. Or the well known expedient of an
hydraulic locking cylinder combined with the steam cylinder may be used to
prevent the piston from moving too far or too quickly.
Instead of the slide-valve and plate a rotating plug or disk valve may be-used-
in combination with a shell or second disk arranged to move proportionally with
the piston. Or the piston may be stationary and the cylinder movable, or the
cylinder and piston may be both movable and be connected to a lever or levers so
as to move differentially, in which cases no plate will be required.
In starting, steering, and analogous engines or machines the small valve will be
moved by hand (directly or through suitable gearing) to the extent to which it is
desired to move the valve gear of main engines, or the rudder of a ship, or other
part, and the part will be immediately moved to that extent by the action of the
pisión or cylinder.