IMPROVE- MENTS IN SELF-ACTING TRAP DOORS FOR MINES
Year: 1857

page_text: LETTERS PATENT to Robert Rennie, of Netherwood, in the County of
Dumbarton, North Britain, Contractor, for the Invention of "IMPROVE-
MENTS IN SELF-ACTING TRAP DOORS FOR MINES."
Sealed the 3rd September 1857, and dated the 19th June 1857.
PROVISIONAL SPECIFICATION left by the said Robert Rennie at the Office
of the Commissioners of Patents, with his Petition, on the 19th June.
.1857..
I, ROBERT RENNIE, of Netherwood, in the County of Dumbarton, North
Britain, Contractor, do hereby declare the nature of the said Invention for
IMPROVEMENTS IN SELF-ACTING TRAP DOORS FOR MINES," to be as follows:-
This Invention relates to the so arranging the trap doors used in mines for
ventilating purposes; and the actuating mechanism of such doors, that the
passage through of the wagons shall open and close the doors without any
manual or secondary interference.
According to one modification of this arrangement the hinge side of the
door has attached to it a back lever-piece, in which is an eye by which
it is jointed to one end of a connecting rod, which passes along the side of
the railway, or working to some distance beyond the door, where its opposite
end is jointed to the back end of a short horizontal lever-piece. There is one

page_text: of these levers at the same distance. on each side of the trap door, each
being set on a vertical stud centre in the ground. These two levers are
connected together by opposed or reversed diagonal rods working through
the partition. These rods are jointed, and attached in such manner that
the rod, jointed at one end of the horizontal lever nearest the rails of the
working, is jointed at its other end to the opposite end of the other horizontal
lever, or that end of this-lever which is furthest from the line of rails. The
other rod is jointed to the levers in a precisely similar way, so that in all cases
when one horizontal lever is moved, the corresponding end of the opposite one
moves in the reverse direction, the corresponding ends of the levers always
approaching to or receding from the trap door in concert. The ends of the
horizontal levers nearest the rails are each fitted with pendant catches or
stop pieces; there are two of these pendant catches in each lever, and
they are hung on stud centres with reverse stops, that is to say, one catch
holds in one direction and gives in the other, and vice versa... The waggons
each carry a projecting pin, or are so provided in other respects that, as
they approach the door, they act upon the pendant catches of the lever on
that side, in such manner as to press forward the front end of the lever;
and this movement, through the agency of the connections herein-before
described, opens the doors just as the horse's head reaches it. The same
action brings forward the corresponding. end of the other lever, so that, when
the waggon has passed through the door, it operates upon this other lever, just
as in the previous instance, closing the door and putting the lever first operated
upon into a proper position for again opening the door on the approach of
a succeeding waggon. This arrangement answers well for the passage of a
single wagon or a short train; but. when it is required to work trap doors for
long trains it becomes necessary to provide such an arrangement as will secure
the opening of the door only just as the horse or wagon approaches it, and
yet allow a sufficient length of time to elapse after the first wagon has passed
through the door for the last of the train to clear before the shutting action
comes into play. This may be effected in various ways, but it is satisfactorily
accomplished, according to one modification, by an arrangement of rocking
shafts or bell crank actions and reverse action levers or catches. One of such
rocking shafts is placed near the door on each side, and each of them is
connected by a back, cord or light rod, with two other rocking shaft or
bell crank movements, which are placed on each side of the door, at the
proper distance from it to allow of the passage of the train. The movements
are also connected with the actual door-closing mechanism in any convenient
manner. The result of this arrangement is, that, when a wagon comes up to

page_text: the closed door, it operates upon the catch of the movement near the door,
and this action opens the door. The latter remains open until the front wagon
has reached the further off rocking shaft or movement on the other side of the
door, when the proper catch of that movement, having been set to the requisite
position by the same action which opened the door, is now acted upon by the
wagon to close the door. In this way, the wagons as they approach the door
always miss the far-out action on that side of the door, and operate upon that
near the door; and on passing through the door the wagons always miss
the rocking shaft action nearest the door on that side, and operate upon
the one furthest away. Various arrangements of operating catches may be
used for this purpose; for instance, the wagons may be caused to act upon
incline-plane pieces or levers disposed at proper distances from the doors, so as
to act in the general manner, herein-before described.
To prevent the doors being left open by foot passengers, a spring or weight
is attached to each, so as to close the doors in the absence of the closing action
of the wagons.