A New or Improved Non-sparking Switch.
Year: 1892

page_text: Date of Application, 18th Aug., 1892-Accepted, 24th Sept., 1892
COMPLETE SPECIFICATION.
A New or Improved Non-sparking Switch.
I, FRANCIS HASTINGS MEDHURST, of Corpus Buildings, Cambridge, Bachelor
of Science of the University of Durham, do hereby declare the nature of this inven-
tion and in what manner the same is to be performed, to be particularly described
and ascertained in and by the following statement :-
My invention relates to a new or improved electric switch which is specially
though not exclusively applicable for use in coal mines, gas works, powder magazines
and factories, petroleum steamers, flour mills and other places where explosive or
readily inflammable materials may be present.
and
or
My invention consists essentially of a vessel of non-conducting material with
means for producing angular movement thereof the said vessel being fitted with
contact pieces and containing a conducting liquid a conducting solid (of such
form that it will readily roll or take up a new position when change of position of
the said vessel takes place) the said conducting liquid or conducting solid, both of
which I shall hereinafter include in the term "bridging conductor" serving to
bridge between the said contact pieces for the purpose of completing the electric
circuit.
Having now described my invention in general terms so as to define its scope
I shall proceed to show how it is to be or may be performed or carried into effect
and for that purpose I shall refer to the accompanying sheets of drawings in which
similar letters of reference indicate similar or equivalent parts.
Figures 1 and 14 are diagrams illustrating the essential features of that form of
my invention in which the bridging conductor takes the form of a conducting
liquid to complete the circuit. In these figures A is a vessel of porcelain or other
suitable non-conducting material. B, B are trunnions upon which the said vessel
rotates or moves angularly. C, C are conducting pieces forming part of
the circuit and which pieces must be electrically connected by the bridging
conductor in order that the circuit may be closed. D is this conductor, in the
present instance shown as consisting of a liquid, say mercury. When the vessel is
in the position shown in Figure 1 it will be seen that the electric circuit is closed.
Let us now assume that the circuit has to be opened. To do this the vessel is
turned through an angle say of 180 degrees into the position shown in Figure 1A.
The contact pieces C, C¹ which were at what was formerly the bottom of the vessel
will be at the position which is now the top of the vessel and the mercury remaining
at the lowest point of the vessel will now no longer connect the pieces C and Ci
and the circuit will now be open.
Figures 2 and 24 and 3 and 3ª represent diagramatically that form of my invention
in which the bridging conductor takes the form of a solid which will readily roll or
take up a new position. The form shown in Figures 2 and 2ª differs from the form
shown in Figures 1 and 1ª merely in the fact that instead of mercury a number of
metal balls is employed. Figures 3 and 34 differ from Figures 2 and 2ª merely in
the shape of the contact pieces and in the fact that a single metal ball is employed
to complete the circuit instead of a number of such metal balls.
Figure 4 represents in side elevation an actual switch constructed under my
invention and which constitutes the best form of carrying my invention into practice
with which I am acquainted at this date. Figure 4ª represents in plan-section on
a plane just below the trunnions the cylinder and contact pieces shown in elevation
in Figure 4. In these figures the switch represented in the position which it
occupies when the circuit is closed. A is a vessel formed in this case of a hollow
cylinder of porcelain closed at one end a, and bearing the trunnions a' a'. 'Near
$

page_text: one end of this cylinder and placed opposite to one another are the contact pieces C, C¹
from which extend outwardly the threaded pins c², c³. The open end of the cylinder
is threaded to receive a threaded stopper or plug E as shown, which is screwed home
when the bridging conductor has been placed in the vessel, the said bridging conductor
being of course inserted in the vessel when the latter is held in the reverse position
to that shown in Figure 4. Upon the pins c², c³ are threaded the binding nuts e, c, c², c²,
the said binding nuts serving for the attachment of the circuit wires or fuses as will
be hereinafter mentioned. Upon the trunnions a¹, a² are fitted the metallic
caps, by means of pins r, y, the said caps being extended in the form of
spindles, forming bearings for the angular movement of the vessel A. The
spindle fits into a recess g in the base G of the switch whilst the spindle bears
in the bracket F and is prolonged through the said bracket to a suitable distance
to enable the handle H to be mounted upon it. 2, 3 are threaded for the purpose
of taking the binding nuts f^, f³, ff. To these binding nuts the leads J J¹ pass
as is shown in the figure and from them again pass the leads j, j. j and j¹ or one of
them may be replaced by fuse wires or a wire. In the Figures 4 and 44 it will be
seen that the parts are in such position that the circuit is closed and that the
current will pass say through,, c³, C, D, C c² j and J1, the bridging conductor D
in this case being shown as consisting of small balls preferably of brass. To open
the circuit the handle H is turned through an angle say of 180 degrees when the
part a of the cylinder will now be in the lowest position and covered by the bridging
conductor whilst the contact pieces C, C' will be raised to the position corresponding
with those shown in Figure 24 and clear from the bridging conductor so that the
circuit will be open or broken. m, m are pins serving as stops to limit the angular
movement to half a revolution and rendering it necessary that at each movement of
the switch the moving parts of the switch should retrace the path of their former
movement, this being essential in the precise form of switch shown in order to
prevent breakage of the circuit wires, which breakage would take place if each
angular movement were made as a continuation in direction of the former movement.
Of these two pins m projects perpendicularly from the base and m' passes through
the spindle in a direction at right angles to the axis thereof, projecting on both
sides of the said spindle to a sufficient distance to come in contact with the pin m.
Figure 5 is an end view of a form of my apparatus in which a cover K is
employed, on which cover are marked the words "On" and "Off" which indicate
the state of the switch according as the arrow upon the handle H points to one
word or the other. The point of the arrow corresponds in position with the closed
end of the cylinder and the feather of the arrow with the open or stoppered end of
the said cylinder.
Figures 6 and 6^ represent in vertical section and in plan respectively a modified
form of part of my apparatus which is of slightly simpler construction than the
corresponding part shown in Figure 4. In this case the contact pieces C, C¹ instead
of passing through the walls of the cylinder A pass through the stopper E. In
other respects it corresponds exactly with Figure 4.
In Figure 4 I have shown the bridging conductor as consisting of metal balls
which may be for example in the case of large switches steel balls such as are
used in cycle bearings or they may be small brass balls or shot formed of hard
metal. Lead shot would not be convenient on account both of the softness and of
the plumbago coating usually present. The rolling of the balls over one another
as the switch is moved keeps the surfaces of the said balls clean by rubbing against
one another. Mercury forms a very good bridging conductor, but I prefer to use
small brass balls. When I use mercury I prefer to use it in sufficient quantity to
well cover the contact pieces and so prevent any chance of sparking above the
surface of the said mercury. I sometimes employ both mercury and brass balls.
As a further precaution to obviate any chance of the formation of an oxide of
mercury I may add a quantity of heavy petroleum which will always float upon
the mercury and prevent any access of air. To prevent any leakage at the
stopper E Imay fasten the same in with plaster of Paris cement or luting or I may

page_text: employ a washer of rubber leather or the like in conjunction with the said stopper
as will be readily understood. Similar precautions may be taken to prevent
leakage round the contact pieces.
I have shown in reference to Figures + and 4* certain means for effecting the
angular movement of the vessel A; but I desire it to be understood that I do not
limit myself to such means as any competent engineer will be able to design many
means for effecting the same result without departing from the spirit of my
invention. For example instead of turning the vessel by means of a handle as
herein before described I may use a push such as is employed in many forms of
switches, the movement of the said push being utilised to cause the angular
movement of the vessel by any of the well known means employed for converting
rectilinear into angular motion. Or I may bring about the angular movement of
the vessel by means of a lever handle such for example as is employed in the well
known Tumler switch where the conversion of the movement might be effected by
a converting device similar to that employed in an ordinary ratchet brace.
It will be seen that no sparking can take place except within the closed vessel
and as it is hermetically closed any sparking which might occur there will not pass
to the atmosphere surrounding the vessel. This fact causes my invention to be
specially applicable for use in such situations as I have hereinbefore mentioned.
It will also be seen that there is no need for introducing any quick break or quick
make device such as have to be employed in ordinary electric switches.
As a further precaution against the formation of an oxide of mercury I sometimes
fill the said vessel with a hydrocarbon vapour or inert gas.
Having now particularly described and ascertained the nature of my said
invention and in what manner the same is to be performed I declare that what
I claim is.
1. In an electric switch the combination of a non-conducting vessel capable of
angular movement, contact pieces fitted to the said vessel, a bridging conductor
and means for angularly moving the said vessel substantially as and for the purpose
set forth.
2. The specific form of switch substantially as set forth with reference to
Figures 4 and 4ª.
3. In a switch such as is herein specified the employment of a stopper fitted
with contact pieces substantially as set forth with reference to Figures 6 and 6^.
Dated this 27th day of July 1892.
F. H. MEDHURST,
Per J. G. L.