Jack's was founded in 2018 by Tesco as a discount chain to rival stores such as Lidl and Aldi. It is named after the Tesco founder, Jack Cohen. The company opened its first stores in Chatteris, Cambridgeshire and Immingham, Lincolnshire on 20 September 2018. Jacks use their flat sides to good advantage when waging a tug-o-war. TACKLE AND BAITS: Most Jacks are fairly small and are caught on the full range of light tackle by anglers seeking other game. If you target larger Jacks, say 10 pounds or more, sturdy spinning, baitcasting and fly tackle should be used, with lines no less than 8-pound test. Jacks synonyms, jacks pronunciation, jacks translation, English dictionary definition of jacks. Often Jack Informal A man; a fellow. One who does odd or heavy jobs; a laborer. One who works in a specified manual trade. Jack, any of numerous species of fishes belonging to the family Carangidae (order Perciformes). The name jack is also applied collectively to the family. Representatives can be found in temperate and tropical portions of the Atlantic, Pacific, and Indian oceans and occasionally in fresh.
Jacks are pieces of material handling equipment that uses force multiplication to lift or move heavy loads. The term jacks can refer to a variety of lifting devices that employ leverage and other methods of mechanical advantage to amplify an applied force to provide the ability to transport a load. Hydraulic jacks are distinguished by their use of an incompressible liquid, such as hydraulic fluid or jack oil, as the means by which force multiplication is achieved. The primary mechanism by which force is applied varies, depending on the specific type of jack, but is typically a screw thread or a hydraulic cylinder. Jacks may be categorized based on the type of mechanism used to generate the lifting force, typically mechanical power, hydraulic power, or pneumatic power.
Mechanical jacks, such as the commonly used car jacks, lift heavy equipment and are rated based on the lifting capacity, which is typically expressed in terms of the number of tons that the jack can handle. Hydraulic jacks tend to have higher lifting capacities than mechanical jacks owing to the amount of force that can be generated by the hydraulic cylinders which produce the lifting action. Common forms of hydraulic jacks include bottle jacks and floor jacks.
Image credit: Mikhail Abramov/Shutterstock.com
Hydraulic Jack Components and Nomenclature
To illustrate the components that are used in a hydraulic jack, a typical manually operated hydraulic jack will be considered. The primary components are discussed below. Note that other smaller components are also used to create the hydraulic jack, such as o-rings, pins, but the primary components shown will be helpful to understand the operation of the jack.
- Reservoir or buffer tank
- Pump with piston or plunger
- Pump lever or handle
- Check valve
- Main cylinder or ram
- Release valve
- Handle
What Are Jacks In Cards
The reservoir or buffer tank is a vessel that holds hydraulic fluid or pump oil which will be used to transfer applied pressure from the pump to the ram. The pump is typically a piston pump that is mechanically activated by moving the pump lever or handle up and down. The handle movement builds up pressure in the hydraulic fluid which transfers that pressurized fluid through a check valve and into the main cylinder. The main cylinder, sometimes referred to as the ram, is driven upwards extending out of the hydraulic jack body by the pressure of the hydraulic fluid, creating the needed lifting force and lifting the load. A release valve is included to release the pressure so that the ram can retract and the load can be lowered.
Some rams are equipped with a threaded extension so that when fully retracted the ram extension can be unscrewed. This feature extends the lifting range for the jack and can eliminate the need to add blocking underneath the jack when the load surface to be lifted is higher than the retracted height of the ram and the jack body.
How A Hydraulic Jack Works
Hydraulic jacks function based on a concept in fluid mechanics known as Pascal’s Principle. Essentially, if two cylinders (a large and a small one) are connected by an incompressible fluid, and a given amount of pressure is applied to one cylinder, that same pressure is imparted to the second cylinder through the fluid connecting them. However, because pressure is equal to force per unit area, the cylinder that has a larger area will experience a force multiplication effect. Even though the pressure on both cylinders is the same, the force which is produced on the larger cylinder will be higher, proportionally higher based on the area of the cylinder.
Pascal’s Principle may be expressed formulaically as follows:
where:
F1 is the applied force to piston 1 (the pump piston)
A1 is the area of piston 1
F2 is the applied force to piston 2 (the ram piston)
A2 is the area of piston 2
By rearranging this equation to express F2 as a function of F1, A1, and A2:
This expression illustrates that the lifting force of a hydraulic jack is amplified directly by the ratio of the surface area of the two pistons.
Hydraulic jacks depend on this basic principle to lift heavy loads: they use pump plungers to move oil through two cylinders. The plunger is first drawn back, which opens the suction valve ball within and draws oil into the pump chamber. As the plunger is pushed forward, the oil moves through an external discharge check valve into the cylinder chamber, and the suction valve closes, which results in pressure building within the ram cylinder.
Types of Hydraulic Jacks
Two common types of hydraulic jacks include bottle jacks and floor jacks.
Bottle Jacks
Bottle jacks became popular in the early 1900s when the automobile industry began to take off. Also called hand jacks, bottle jacks provided an easy way for an individual to lift a vehicle for roadside inspection or service. The design of the hydraulic bottle jack resembles a milk bottle, thus earning bottle jacks their name—today, they range in size and lifting capability from one hundred pounds to several tons. How does a bottle jack work? Bottle jacks feature a vertical shaft, which supports a platform (called a bearing pad) that directly bears the weight of the object as it is lifted.
Although they are most commonly used in the automobile industry (1.5 to 5-ton jacks are the range of capacities typically used to lift cars), bottle jacks have other uses as well. In the medical industry, they can be used in hydraulic stretchers and patient lifts. In industrial applications, they can be found as pipe benders used in plumbing, in cable slicers for electrical projects, and as material lifts within warehouses. Their ability to lift heavy loads plays a big role in enabling the repair of large agricultural machinery and in many construction operations. Bottle jacks can be secured within a frame, mounted on a beam, or simply used as free-standing to allow for repositioning as needed.
Floor Jacks
What is a floor jack? Unlike bottle jack shafts which operate vertically, the shaft in a floor jack is horizontal—the shaft pushes on a crank that connects to a lifting pad, which is then lifted vertically. Floor jacks typically provide a greater range of vertical lift than bottle jacks and are available in two sizes. The original jack is about four feet long, a foot wide, and weighs around 200 pounds—they can lift 4-10 tons. A more compact model was later made, which is about three feet in length and can lift 11/2 tons. Although “mini jacks” are also produced, they are not a recognized standard type of floor jack. Typically, one of the first two sizes should be used.
Other Types of Jacks
Toe Lift Hydraulic Jacks
Toe lift hydraulic jacks are a specific type of hydraulic jack that can be used to lift machinery and other loads where the clearance between the ground and the bottom surface of the load is low. This special type of jack works in situations where a bottle jack or floor jack would not function due to the low ground clearance of the load.
Leveling Jacks
Leveling jacks make use of a mechanical screw mechanism and are portable, often used to level trailers, RVs, and the like.
Scissor Jacks
Scissor jacks are compact jacks that use a mechanical screw whose rotation results in the raising or lowering of a set of scissoring arms that extend or retract depending on the position of the screw mechanism.
Screw Jacks
Screw jacks are mechanical jacks that use a vertical screw mechanism to raise or lower the jack. Some models are wrench adjustable while others employ a level inserted through a hole in the jack to allow for additional mechanical advantage to use when turning the screw lift the load.
Ratchet Jacks
Ratchet jacks make use of a pawl and ratchet mechanism for raising or lifting a load. At one time, ratchet jacks were the de facto standard type of jack that automobile manufacturers included with their vehicles for owners to use when changing a flat tire. The jack would be positioned to attach to the front or rear bumper of the car and the tire wrench served as both a jack handle and a lug nut wrench. With the development of unibody construction and the elimination of metal bumpers on automobiles, ratchet jacks faded from use in favor of scissor jacks which had a lower profile, allowing for them to slip under the unibody and access designated lift points.
Hydraulic Cylinder Failure Mechanisms and Causes
The hydraulic cylinders used in jacks can experience failures requiring servicing or cylinder replacement to restore the jack to a safe operating condition. Some common failure mechanisms for hydraulic cylinders include:
- Hydraulic fluid contamination, which can cause particulates to score or damage the cylinder, or where contamination of the fluid can result in deterioration of the hydraulic seals.
- Seal leakage, which causes loss of cylinder pressure, impacting the lifting capacity of the jack, and which may continue to worsen over time and become more pronounced unless seals are replaced.
- Impacts of side-loading, wherein the force vector for the application of the load to the cylinder has a component that is not parallel to the axis of the cylinder itself.
- Failure to maintain proper pressure in the cylinder, which can exacerbate fluid leakage from seals.
- Improper maintenance, where the hydraulic cylinder was not given regular inspections and general recommended maintenance, leading to a reduction in service life and device failure.
Applications for Jacks
Jacks have wide applications in different industries and are used to lift and transport heavy loads, relieve vertical forces from weight-bearing members so repairs can be made, and are valuable pieces of equipment in the construction, shipbuilding, automotive repair, as well as other specialized industries. Among the applications for jacks are:
- Automotive, such as for transmissions and engine testing
- Shoring and stabilizing such as for tunnels and mines
- Tractors & Trailers
What Are Jacks
Specifications for Jacks and Hydraulic Jacks
Jacks including hydraulic jacks are typically specified by several key specifications which are outlined below. Note that these parameters may vary by jack type and may also vary from manufacturer to manufacturer.
- Capacity – represents the maximum load that the jack is capable of lifting, usually expressed in tons or pounds.
- Maximum lift height – represents the largest distance or displacement of the jack’s ram or lift pad when the jack is in the fully extended position measured to the ground or a reference surface.
- Travel length – is the maximum distance over which the ram or lift pad will travel or move from its un-extended to its fully-extended positions.
- Working orientation – indicates the intended use orientation for the jack (vertical or horizontal) based on the design of the unit.
- Handle length – the overall length of the handle for raising and lowering the jack.
- Power source – indicates the mechanism by which the jack is operated, such as manual, air or pneumatic, battery, or electric, for example.
Summary
Hydraulic jacks can lift heavy loads but require maintenance to preclude the development of problems with the hydraulic components that could endanger operators, such as problems with the cylinders that assist in generating the lifting force.
This article provided information on jacks with a specific focus on hydraulic jacks. To learn more about other types of lifting mechanisms, consult our guide on lifts, or visit the Thomas Supplier Discovery Platform to locate related suppliers for lifts, hydraulic jacks, or hydraulic cylinder repair services.
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