Improvements in Air-compressing Pumps.
Year: 1887

page_text: Date of Application, 29th July, 1887.
Specification Accepted, 30th Aug., 1887.
Improvements in Air-compressing Pumps.
I, HENRY DAVEY, of 3 Prince's Street, Westminster, in the county of Middlesex,
Engineer, do hereby declare the nature of this invention and in what manner the
same is to be performed, to be particularly described and ascertained in and by the
following statement :-
My invention consists in means whereby the resistance of an air-compressing
pump may be kept constant, or nearly so, whilst the pressure of air in the receiver,
into which the pump is made to deliver its air, is increasing. For this purpose I
cause the effective capacity of the pump to be varied, as the pressure of the air is
increased, by causing the compression to be commenced at varying points in the
stroke, either by opening or closing passages in the side of the pump cylinder by
hand, or by automatically opening or closing a passage at varying times by means
of the governor of the engine, or by the variation of pressure in the air receiver, or
by any other convenient method.
Referring to the drawings: A is an air-compressing cylinder of which B is the
piston is the suction valve working in the delivery valve D.
The delivery valve D is kept against the face of the cylinder by means of a spring E,
and the suction valve C is kept against its beat in the delivery valve D by means of a
spring F.
G is a valve which may be opened by hand thus making communication
between the cylinder A and the atmosphere, through the passage H. If then the
valve G be opened, compression will not cominence until the piston B has covered the
passage H, and thus cut off communication between the cylinder and the atmosphere.
If the valve G be placed, as shewn, in the centre of the cylinder, then when it is
opened the cylinder will contain only half its capacity of air when compression begins.
Similar valves to G might be placed at intervals in the side of the cylinder, so that
by opening them successively, as the pressure in the air receiver increases, the volume
of air contained in the cylinder at the time of compression might be varied.
To regulate automatically the admission of air into the cylinder I intercept the
communication of the valve C with the atmosphere by the valve K, which is kept
closed by means of a spring N. On the crank shaft Z is an eccentric P, Fig. 2,
fixed in the same position as the crank which works the pump piston. The said

page_text: eccentric is made to actuate a spindle Q, working in the guide R. Between the end
of the spindle Q and the spindle of the valve K is inserted a wedge S, which is
connected to the arm T of a bent lever. The governor W, driven from the crank
shaft Z, is made to actuate the arm V of the said bent lever, and thus raises or
lowers the wedge S. When the said wedge is raised to its full height the travel of
the eccentric P will be insufficient to enable it to open the valve K, and when the
wedge is depressed to its full extent the valve, will have the same travel as the
eccentric and will open wide.
The effect of this will be that if the speed of the engine should decrease, owing to
the increase of work to be done through the rise of pressure in the air receiver, the
governor will raise the wedge S, and by thus shortening the time during which the
valve K will be open it will diminish the quantity of air admitted into the cylinder.
The variation in the opening and closing of the valve K may be effected in many
other known ways, such as, by a moveable eccentric whose position is determined by
the governor of the engine, or by the varying pressure in the air receiver, or in other
ways.
Having now described my invention and the manner in which it may be carried
out, I claim,
Varying the amount of air to be compressed in an air-compressing pump in the
manner substantially as described and illustrated.
Ph: 50th
Tl 1007