HYDRAULIC JACK.
A Lifting-Jackis a contrivance for raising great weights by force from below; also calleda 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 bya screw, whereas—a hydraulic jackis a jack or lifting apparatus operated by someliquid, usually oil, acting against a piston or plunger, the pressure on the liquid being produced by a force pump.The hydraulic jackconsists 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 byFig. 138. TheFig. 137on the opposite page shows the inside view ofFig. 138but on a different scale.The names of the partsare particularly to be noted.
Fig. 138.
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 footis usually made of cast iron or cast steel and may be either round or square to suit requirements.The cylinderis bored from a seamless steel ingot and having a thread upon its lower end is screwed into the base.
The ramis 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 heightor 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.
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 jacksthe 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.
Fig. 139.
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 cylinderthe 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 leverall 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 pumpremove 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 reservoirremove 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 usethe 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.
Fig. 140.
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.
Fig. 141.
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.
Fig. 142.
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 describedin 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 legsor 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.
Fig. 143.
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. Thepunch 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.
Fig. 144.
Fig. 144.
Fig. 145.
Fig. 145.