_A Lifting-Jack_ is a contrivance for raising great weights by force
from below; also called _a jack-screw_. From its derivation from
Jack, equivalent to lad or boy, has arisen its modern use as denoting
a contrivance which is subject to rough usage. It is operated by _a
screw_, whereas—_a hydraulic jack_ is a jack or lifting apparatus
operated by some _liquid_, usually oil, acting against a piston or
plunger, the pressure on the liquid being produced by a force pump.
_The hydraulic jack_ consists of, 1, a cylinder; 2, a ram or plunger;
and 3, a pump. One of these machines is shown and described in the
Glossary, page 24, another is illustrated by Fig. 138. The Fig. 137 on
the opposite page shows the inside view of Fig. 138 but on a different
scale. _The names of the parts_ are particularly to be noted.
[Illustration: FIG. 138.]
Movable hydraulic, or screw, jacks serve on numerous occasions most
effectively for lifting or propping-up of less accessible parts.
Eye-bolts and jack-bolts are arranged for, in all parts that are likely
to be handled, to facilitate and accelerate the work in necessarily
crowded quarters.
_The base or foot_ is usually made of cast iron or cast steel and may
be either round or square to suit requirements. _The cylinder_ is bored
from a seamless steel ingot and having a thread upon its lower end is
screwed into the base.
_The ram_ is also a tube of seamless steel having a thread at the top
and is screwed into the head or cap which is made either of cast iron
or cast steel. The lower end of the ram has a thread inside to receive
the pump plug which contains the delivery valve, while upon its outside
is placed the cup leather packing and the ram packing ring. The pump
for operating the ram is from five-eighths to three-quarters of an inch
in diameter depending upon the capacity of the jack, and has a plunger
packed with a cup leather.
A suction valve is contained within the plunger. A short arm is fitted
upon a socket which enters through the side of the head or reservoir.
This arm is connected by a pin to the pump inside the ram while the
outer end of the socket has a tapered rectangular hole through it to
receive the jack-lever. A leather collar packing makes the socket tight
where it enters the side of the reservoir.
_To properly use a hydraulic jack._ Place the head under the weight to
be raised, be careful to set the jack plumb with a good solid footing;
put the lever into the socket with its projection on the bottom side;
work the lever until the weight has been raised to the desired height
_or an escape of liquid blows out of the safety vent_. Hold the lever
up or raise it to its highest position and remove it from the socket
to prevent the valve from opening. In lowering insert the lever in
the socket with the projection underneath and then cautiously press
it slowly down until it brings up against the stop; remove the lever
and turn it over with the projection on top; insert the lever in the
socket and gently but firmly press it on the end with the right hand
clasping the ram with the fore finger, and thumb of the left hand: thus
the workman has full control of the jack and can lower and stop as
frequently as may be found necessary.
If from any cause the valves stick a few sharp quick strokes of the
lever will usually release it and cause it to work, if not, it should
be thoroughly cleaned.
Before shipping the brass filling screw should always be screwed down
tight, and before using this screw should always be loosened to let the
air out and in.
NOTE.—A prominent firm making these tools says: “In our Jacks, rams
are cut and cylinders bored from solid high carbon steel. We have
nearly 300 styles for pushing, pulling or lifting.” This shows the
wide use to which hydraulic jacks are put; the style shown in the
Glossary with its broad base is to be used when the jack stands
upon a light board on the ground and can be placed under the work,
or where steadiness is required. Fig. 139 shows a style to be used
when there is not room enough to get the head of the jack under the
work, and is the style generally used for moving engines, boilers,
machinery, etc.
_In repairing hydraulic jacks_ the following points should be carefully
observed; before attempting to repair a hydraulic jack the trouble
should be definitely located, next:
Put the jack under a weight and attempt to raise it, carefully watching
its action. Should the liquid leak out around the lever socket, the
gland should be tightened slightly until this leak disappears. If the
packing is worn out unscrew the set screw at the back of the head about
one-quarter inch, then withdraw the socket not more than one inch,
unscrew the gland and put in a new packing of lamp wick braided and
well oiled with mineral oil, which is free from gum. Afterwards put the
socket back to its former place and tighten the set screw.
When the pump valve leaks the lever can be worked up and down without
raising the ram. This is also true when the plunger packing becomes
worn. If the trouble is found with the valve it can be ground by taking
out the pump plug and unscrewing the brass bonnet which covers the
valve.
[Illustration: FIG. 139.]
Sometimes the jack will become air bound by reason of the accumulation
of dirt around the filling plug; this must be removed before the jack
will work. Sometimes the liquid will all have been displaced before the
ram is half way up, in this emergency the reservoir must be refilled.
It often happens that when the workman stops working the lever it
will persist in rising to its highest position. This indicates the
presence of dirt under the lower or delivery valve. One or two sharp
quick strokes of the lever will generally dislodge such obstructions;
if this does not bring relief the valve is probably worn so as to need
regrinding. _When a jack has been taken apart each part should be
thoroughly washed in clean water._
While using, _if the liquid escapes over the top of the cylinder_
the ram packing is too loose, and may be set out by inserting a
strip or strips of tin or any sheet metal between the leather and
the ram packing ring; all leathers should be kept soft and pliable
by saturating with a proper leather dressing such as Frank Miller’s
Leather Preservative or Shoemakers’ Dubbing. Castor Oil is excellent as
well.
_One man can exert upon the lever_ all the pressure that the jack is
capable of raising and this pressure should not exceed 150 lbs. Beyond
this the jack will be strained.
_To repack the pump_ remove the pump plug, and unscrew the set screw in
the head, then withdraw the socket far enough to permit it to revolve
clear of the lug, on the head, which brings the piston head out of the
pump.
After the new packing is in place the piston should be worked in and
out a few strokes to see if it is right, then replace the plug.
_To fill the reservoir_ remove the filling screw in the top of the
head, and fill with a mixture of proof alcohol (95 per cent.), two
parts and water three parts for winter use, or for summer use one part
alcohol to four parts water.
_When not in use_ the ram in a hydraulic jack should be kept in its
lowest position, that is to say, all the way down, _or in_, as the case
may be.
IMPORTANT.—Jacks should never be filled with kerosene oil, water or
wood alcohol, for the following reasons: Kerosene oil destroys the
leather packing, water will rust the parts and make them rough, while
wood alcohol attacks the smooth steel surfaces, and thus destroys
both the cylinder and ram. All liquids should be well strained before
putting them into the reservoir and great care should be exercised to
prevent any dirt from getting into this reservoir.
_The Pulling Jack._—The pulling jack, Fig. 139, is used in connection
with travelling cranes over wheel presses, quartering machines,
planers, drill presses and lathes. Its operation is the reverse of
lifting jacks.
This Jack has an improved force-pump on the outside, worked by a lever,
which draws the liquid from the upper end and forces it into the space
on the opposite side of the piston. The piston rod has one of the rings
attached at the end.
By this operation the rings are drawn together and with them the body
to be lifted or moved, for it will be understood that this style of
jack works either in a horizontal or vertical position. Hooks are
furnished instead of rings when desired.
The liquid is introduced into a hole in the side of cylinder, care,
being observed to push the piston into the cylinder. The proportions of
filling liquid are proof alcohol two parts and water three parts.
To use this jack extend it as far as it can be pulled apart, first
opening the valve in the side of force-pump. Now close this valve and
work the pump lever.
This jack appeals particularly to the marine engineer, to be attached
to the trolley over the engine for the purpose of raising pistons, rods
and lifting various parts of the machinery.
[Illustration: FIG. 140.]
_Horizontal Jack._—The accompanying engraving, Fig. 140, shows a
horizontal type for pulling armatures on to shafts, putting in cranks
pins, and marine work. The directions given for the care and handling
of the regular hydraulic jack apply also to this as well as other
devices of the same description.
This pump has two plungers of different diameters, the small one inside
of the large, so that by throwing a clutch, both plungers may work
together as one, or they may be separated, and the smaller one used; as
for example, in starting, the larger pump is used as far as possible,
_i.e._, until the pressure becomes too great for the large plunger,
then the clutch is thrown and the smaller one finishes the work.
The speed of this appliance may be changed to three times greater, and
its power reduced to one-third of the maximum by throwing the clutch
which brings the large plunger into operation. A rack and pinion
with handle is connected with the main ram to cause its return when
forced out to its full length. The size shown in Fig. 140 represents a
capacity of 200 tons and its approximate weight is 1,200 lbs.
[Illustration: FIG. 141.]
_The Hydraulic Bolt Extractor._—Much harm is done to coupling bolts
in driving them out with a hammer or sledge. The hydraulic bolt
extractor shown in Fig. 141 is an admirable device to do this work
without injuring the bolts or threads. This same apparatus may be used
for other purposes as well as that for which it was designed, as will
appear from time to time.
_The Hydraulic Punch._—The hydraulic punch has been found of greatest
utility in the erection of steel structures, such as buildings, bridges
and ship building. It consists of a hydraulic jack attached to a
“punching bear” instead of the usual screw to operate the punch. By
an ingenious device the punch can be shoved down close upon the work
without pumping all the way, as in the earlier styles of hydraulic
punches; this means a considerable saving of time and muscle.
[Illustration: FIG. 142.]
The construction and operation of working parts of this punch will be
easily understood by referring to the engraving, Fig. 142 where 18
represents the body or “punching bear,” 17 the ram, 19 the raising and
lowering pinion to move the ram quickly to its work; 20 shows the die
with punch in place above it, secured by its gland; 3 the punch head
cistern, the screwed cover having a hole in its center to guide the end
2 of pump plunger 9, having cup leather packing 10, at its lower end;
5 represents the lower socket which carries the arm 4 to operate the
piston 6. The suction valve 11 is supported by the spring underneath;
12 is the safety vent; 13 the release or lowering valve operated by
the stem 7 which is pushed downward by the projection of the piston 6
whenever the lever is turned and pressed downwards as described in
lowering the lifting jacks. The relief valve is kept seated by the
spring 14. 8 represents the body of the pump 16 its packing and 15 the
ram packing ring. No. 16 does not move, but the ram 17 does, having
a cup leather reversed at its upper end applied in the same way and
manner as 16, with screwed packing ring. The discharge valve is located
behind the pump plunger 9 and is, therefore, invisible.
_A hydraulic punch mounted upon three legs_ or supports is shown in
Fig. 143, and it also has a shackle at its back to suspend the punch in
mid air as occasion requires.
[Illustration: FIG. 143.]
The details of this punch are like Fig. 142. It has two guards, one
each side of the punch to pull the material operated upon off the punch
as it is raised by the lower lever. Another very convenient style of
hydraulic punch is shown in Fig. 144 where A represents the body of
punch, B the operating lever with the lowering or adjusting lever shown
broken off. The punch proper is shown at C. The center of gravity
of this punch has been so nicely located that by suspending from the
handle the ram hangs plumb.
[Illustration: FIG. 144.] [Illustration: FIG. 145.]