APPARATUS FOR INDICATING THE SPEED OF MARINE ENGINES."
Year: 1876

page_text: PROVISIONAL SPECIFICATION left by Beauchamp Tower at the Office of the
Commissioners of Patents on the 24th October 1876.
BEAUCHAMP TOWER, of Moreton, in the County of Essex.
APPARATUS FOR INDICATING THE SPEED OF MARINE ENGINES."
"IMPROVEMENTS IN
My Invention relates to apparatus whereby the speed or number of revolutions
per minute of a marine engine can be visibly indicated in various parts of the
vessel, as for example, on the deck or bridge, or in the cabin or elsewhere. For this
purpose I employ arrangements similar in principle to those described in a Provisional
Specification filed by me on the 28 May, 1874, No. 1872, my present Invention
consisting chiefly in practical improvements in these arrangements and particularly
in the construction of the gauges or indicators employed in combination therewith.
As described in the Specification referred to I cause the engine to work a centri-
fugal or rotary pump, so as to establish a difference of pressure of water or other
liquid in its suction and delivery pipes, which pipes I extend side by side to the
various parts of the vessel where it is desired to indicate speed, terminating the
suction pipe in a cistern head, and closing the upper end of the delivery pipe after
working the pump for some time to get rid of air.
The difference of pressure in the two pipes at any level being the result of the
speed at which the pump is driven, it is only necessary at any part of these pipes to
ascertain the difference of pressure by means of a suitable pressure gauge in order
to determine the speed of the pump, and consequently that of the engine from
which it is driven, either directly or by intermediate gearing. The gauge which I
employ for this purpose is of the following construction :-I provide a box with
corrugated sides, like that used in an aneriod barometer, and I place it within a tight
casing, connecting the interior of the box with one of the two pump pipes, and the
space in the casing exterior to the box with the other pipe. Both the box and the
casing being thus charged with liquid, that in the one having a different pressure
from that in the other, the sides of the box are caused to bend outwards or inwards
inore or less according to the difference of pressure within it and without it, that
is to say, in the two pump pipes. I place the indicating mechanism within the casing
so that there is no spindle or rod passing through a stuffing box, and consequently
the pressure box is free to operate without sensible resistance.
I cause one side of the box to bear against a spring which is connected by a con-

page_text: necting rod to a crank on a spindle, and this spindle works by multiplying gear,
another spindle carrying an index round a dial graduated to shew the speed or the
number of revolutions per minute made by the engine.
As the difference of pressure in the pump pipes depends not on the velocity
simply, but on the square of the velocity if the index moved over equal distances
for equal changes of pressure, the graduations of the dial representing corresponding
variations of speed would be very unequal; in order to render them less unequal I
so arrange the crank and connecting rod that they are nearly in one line, or the crank
is only a little away from its dead centre when there is no difference of pressure in
the two pipes, and that it is moved to half stroke or nearly one quarter of a
revolution round when the difference of pressure is at its maximum.
The side of the casing over the dial is made of glass, so that the index can be
seen through it, and I find it also convenient to make the opposite side of glass,
and the dial itself of frosted glass or enamel, so that it can be illuminated by a light
placed behind the gauge. I prefer to make the index of vulcanite or some such
material having a specific gravity near that of the liquid in which it is immersed
so that its weight is in balance, and to apply a light spring to its spindle to prevent
back lash in the gearing by which it is connected to the crank spindle, I prefer
also to make the mechanism of the gauge of incorrodible or un-oxidisable metal or
to plate it therewith.