IMPROVEMENTS IN PULLEY BLOCKS, PARTS OF WHICH IMPROVEMENTS ARE ALSO APPLICABLE TO CRANES AND OTHER LIKE APPARATUS."
Year: 1881

page_text: PROVISIONAL SPECIFICATION left by Thomas Henry Ward and Edmund
Howl at the Office of the Commissioners of Patents on the 19th April 1881.
THOMAS HENRY WARD and EDMUND HOWL, both of the Firm of Howl, Ward,
and Howl, Engineers, of Tipton, in the County of Stafford. IMPROVEMENTS IN
PULLEY BLOCKS, PARTS OF WHICH IMPROVEMENTS ARE ALSO APPLICABLE TO
CRANES AND OTHER LIKE APPARATUS."
$6
Our Invention relates to improvements in pulley blocks, parts of which
improvements are also applicable to cranes, over head travellers, and other like
apparatus, and it has reference more particularly to improvements in differential
self sustained pulley blocks of the description known as Weston's, the principal
object of the Invention being to overcome the difficulties which have been
experienced in the use of the Weston blocks, and obtain a block having all the
advantages of a Weston block when raising and in repose, whilst providing that a
load shall be capable of being released and thereby lowered without power, safely
and surely, so that in the hands of the ignorant there is no risk of damaging either
life or property, as the slightest inattention merely ensures the block returning to
its self sustaining element again, leaving the load suspended as before.
In order to accomplish the object before mentioned, we reduce the velocity ratio
to such a quantity, both for large and small size blocks, that the friction is slightly
in excess of the mechanical efficiency, and in those cases in which purchase gear is
necessary over and above the velocity ratio, as for example, in large blocks, we add
it as a separate gear of a suitable description.
In carrying out the principle feature of our Invention we combine an improvement
in the Weston friction coupling and brake with the Weston pulley block. We
construct the bottom sheave in a similar manner to that adopted by Weston, but
we cast the two top sheaves separate the one from the other, but arrange them in
such a manner that so long as these two sheaves are gripped together tightly, they
are to all intents and purposes equivalent to being cast as one, consequently they
turn as a Weston sheave; but when they are released from each other they run
down by gravity independently in opposite directions by virtue of the half load
hanging from each of these sheaves.

page_text: The shaft or axle round which the sheaves rotate serves also as a bolt, and a
collar at the one end serves as a head to that bolt; this bolt is screwed at the other
end with a quick thread, and the large sheave serves as a nut to the same whilst
the other sheave runs loosely upon it, but is prevented from sliding in either
direction along the axis by means of the said collar or head.
As before stated the sheaves grip each other, and for this purpose their inside
surfaces are turned after the manner of friction cones, male and female respectively;
upon the shaft or bolt one or more spockets wheels are fixed.
The apparatus operates in the following manner:-
In raising, the spocket wheel is turned in the same direction as in a Weston
block, the half load hanging from a large sheave or nut runs up the screw and
grips the small sheave (which is running in the other direction between it and the
head of the bolt, turning them together as a Weston. In lowering, the spocket
wheel is turned in the opposite direction; by so doing the friction surfaces are
released, since it takes less power to unscrew these surfaces than it does to turn the
block; the load is lowered safely and surely, but by means of gravity instead of
power; the load lowers as long as the spocket wheel is rotated only, the sheaves
gripping each other and resting the load without any shock when the spocket
ceases rotating.
Thus it will be seen that in raising the load the block operates after the manner
of a Weston block, but in lowering it operates in the manner provided by our
Invention.
The Invention may be somewhat modified in its details, but the following
examples are given as types of arrangements which may be adopted.
A small sheaf is provided running loose on the shaft, but prevented from sliding
along its axis by a collar in one direction and by a collar or head in the other
direction. The large sheave serves as a nut to the shaft, which is screwed at one
end. Spocket wheels are keyed to the shaft, and friction cones are formed on the
respective sheaves.
In lieu of employing two spocket wheels at opposite ends of the shaft, or a single
spocket wheel at one end of the shaft, a single spocket wheel may be arranged in
the centre between a suspension bridle, whilst the divided sheaves are arranged
symetrically at opposite sides of the same a more perfect balance is thus obtained
whilst raising the load, and economy in head room is also effected, and the usual
frame is dispensed with. In order to accomplish this result however it is clear
that the friction cones cannot face each other as before, therefore they are situated
on the outer sides, the thrust upon them being outwards instead of inwards. A pair
of intermediate cone plates fixed rigidly on a central shaft are therefore added, so
that the motion of the screw shall be independent of that of the cone shaft, one
shaft being inside the other.
The arrangement last herein before described may be modified in order to
obtain a double purchase power as suited more particularly for the large size
blocks, by introducing a worm and worm wheel or equivalent gearing between the
spocket wheel or wheels and the main shaft, the said worm and worm wheel or
gearing being by preference arranged centrally between the divided sheaves.
The sheaves may be proportioned so that as a Weston block they are scarcely
self sustaining in themselves, but that the friction introduced on the worm
and wheel is sufficient to make up the difference and thereby secure it as a self
sustained block. In this arrangement also the lowering element by gravity, as in
the last case, can be introduced by releasing the worm or the worm wheel on its
shaft, the parts being caused to reengage by means of friction cones actuated by a
spocket wheel or lever.
It is obvious that the double purchase or worm gear can be added to the block
constructed in accordance with the first example.
:
A modification of the arrangement in which the central spocket wheel is used
consists in keying the sheaves on to one shaft as a Weston block pure and simple,

page_text: that is, to raise and lower as a Weston block, an important feature of our Invention
being to arrange the divided sheaves at opposite sides of a central suspension, with
the power applied at the centre and the load at the extremities of the shaft. If
desired the double purchase gear may be added as hereinbefore described.
As further examples of modifications which may be used in the details, the
ordinary hook and frame may be applied, or the sheaves may have a velocity ratio
greater than that assumed, consequently large sheaves or separate break gear may
be added, such modifications not affecting the principle of our Invention.