IMPROVEMENTS IN Hydraulic CRANES
Year: 1877

page_text: PROVISIONAL SPECIFICATION left by George Low at the Office of the Com-
missioners of Patents on the 14th July 1877.
GEORGE LOW, of Ipswich, in the County of Suffolk, "IMPROVEMENTS IN Hydraulic
CRANES."
This Invention has for its object improvements in hydraulic cranes. I construct
such cranes with a jib moveable about an horizontal axis, so that it can travel
through the vertical from one side to the other of its standard or support. This
motion is given to the jib by connecting it with an hydraulic press, to the cylinder
of which water under pressure is admitted by a valve.
The valve is controlled automatically by instruments in connection with the jib, and
operating so that the valve, having been opened by hand to admit water to the press,
and raise the jib with the load attached to it, as the jib passes the vertical, the supply
passage is automatically closed, and the exhaust opened so as to allow the jib to descend
on the other side, and when the jib has reached the point to which the apparatus has
been previously set, the exhaust is in turn closed, and the water being imprisoned
in the cylinder of the press, the jib is brought to rest.
The valve which I employ is a disc held by the pressure of the supply against a
face in which passages leading into a chamber open at all times to the cylinder of
the press. The valve disc has a hollow stem passing out of the valve box through
a stuffing box, and receiving a handle by which the valve can be turned. The
sectional area of the valve stem is such as to adjust suitably the pressure of the
valve on the valve face.
The exhaust takes place through the stem of the valve which is in communication
with the exhaust passages in the face of the disc.
The valve works through an are of somewhat less than half a circle, its play being
limited by stops. When the valve is at either end of its course, the supply is open
to the cylinder of the press.
At two intermediate points the valve closes entirely the passages leading to the
cylinder, and when the valve is in its central position, the exhaust from the cylinder
is full open.
The stem of the valve has upon it two tappet arms, and on the same axis with
the jib of the crane there are three arms or wipers.

page_text: The action of these parts is as follows:-In order to raise the jib with its load,
the valve is moved by hand to one or other of its two extreme positions, according
to the side on which the jib happens to stand at the time. Thus, the jib is brought
to the vertical position, and one of the arms or wipers moving with the jib strikes
the tappet or arm on the stem of the valve, and moves the valve at once to its
central position, thereby opening the exhaust and permitting the motion of the jib
to be continued by its own weight until another of the arms or wipers upon the
axis of the jib comes round, and in a similar manner moves the valve further,
thereby closing the passages leading to the cylinder, and stopping the further motion
of the jib.
To cause the return of the jib, the valve is moved a step further in the same
direction, and the automatic actions repeat themselves, first, when the jib reaches
the vertical position, the central wiper causes the exhaust to be opened, and after-
wards when the jib has descended sufficiently far, the other outer wiper (which in the
previous stroke was inoperative) sets the valve so as to close the cylinder of the
press, preventing the escape of the water from it, and so bringing the jib to rest.
There is a relief valve to prevent the cylinder being exposed to undue strains,
and permitting the water to pass back to the supply when the pressure in the
cylinder exceeds that in the supply pipe. A valve in the exhaust passage serves to
regulate the speed of motion.
For the purpose of raising and lowering independently of the movement of the
jib, the crane is supplied with another hydraulic press which actuates a pitch
chain gearing with a pinion, the axis of which is carried upon the jib. On
the same axis there is also a drum upon which the crane chain is wound, and
the chain passes from the drum over guide pulleys of the jib head to the load.
The size of the drum is such as to multiply to the desired extent the motion
of the pitch chain. The chain is led from the drum on the side of the axis on which
the pitch chain operates upon the pinion. The arrangement at the jib head is such
as to admit of the load swinging clear as it passes from side to side.