How does Hydraulic Jacks Function?

How does Hydraulic Jacks Function

Jacks are components of equipment for handling materials that make use of force multiplication to lift or move large loads. The term”jacks” could describe various lifting devices that use leverage, as well as other strategies that use mechanical power to increase the force applied to give the capability of moving loads. Hydraulic Jacks differ by using an incompressible liquid, that is, hydraulic oil or even jack oil as the mechanism through which force multiplier can be achieved. The principal mechanism through which the force is applied differs according to the jack type, but it’s usually either a screw thread or a hydraulic cylinder. Jacks are classified by the mechanism that generates the lifting force, typically electrical or hydraulic and pneumatic.

Mechanical jacks, like the most commonly utilized car jacks, can lift large equipment and are evaluated according to their capacity, usually measured by the number of tons the jack can lift. However, hydraulic jacks generally are more powerful than mechanical jacks due to the force produced by the hydraulic pistons that generate the lifting effect. The most common types of hydraulic jacks are bottle jacks and floor jacks. 

Hydraulic Jack Components and Nomenclature

A typical hydraulic jack operated by hand will be examined to demonstrate the components used in the hydraulic jack. The main components are described below. It is important to note that other components can also be used in the construction of the hydraulic jack, for instance, pins and o rings, but the components shown in the first place can be useful in understanding the workings of the jack.

  • Reservoir or buffer tank
  • Pump with plunger or piston
  • Lever or handle for pump
  • Check valve
  • Main cylinder, also known as the ram
  • Release valve
  • Handle

The buffer tank or reservoir is a container that stores the hydraulic fluid, also known as pump oil, used to transfer the tension from the pump into the ram. The pump usually has a piston and is activated mechanically by moving the lever or handle upwards and downwards. The handle’s movement creates tension in the hydraulic fluid, which moves that pressurized fluid via a check valve in the main cylinder. This cylinder, also called the ram, is moved upwards, extending out from the hydraulic jack body due to a hydraulic fluid’s pressure generating the required lift force and raising the weight. A release valve is built to relieve the pressure so that the ram can retract and the load can be reduced.

Certain rams come with an extension threaded to ensure that, when fully retracting, the extension of the ram can be removed. This feature can extend the lifting capacity of the jack, and eliminates the requirement for blocking under the jack if the load’s surface to be lifted is larger than the height that can be retracted between the ram and body of the jack.

How A Hydraulic Jack Works

Hydraulic Jacks are based on a principle in fluid mechanics referred to by the name Pascal’s Principle. In essence, when an incompressible liquid joins two cylinders (a larger and a smaller one), and a certain volume of force is established on one of the cylinders, the same pressure is transferred to the other cylinder by the fluid that connects them. But, since pressure equals the force per square inch, the cylinder with a greater area will suffer an effect of a force multiplier. While the pressure of both cylinders is equal, the force generated by bigger cylinders will ultimately be more in proportion to the size of the cylinder.

Pascal’s Principle can be expressed as a formula like this where:

  • F 1. is the force applied on piston 1. (the piston of the pump)
  • The area of piston 1, which is the area of piston 1, is the size of piston 1.
  • F 2. is the force that is applied to piston 2 (the piston of the ram)
  • The area of piston 2. is the area of piston 2

Hydraulic jacks work on this fundamental Principle to lift large weights: they utilize pump plungers to transfer oil through two cylindrical cylinders. The plunger is initially drawn back, allowing the suction valve to open within and then drawing oil into the chamber of the pump. As the plunger moves upwards, the liquid flows across an internal discharge check valve and into the cylinder chamber. Finally, the suction valve is closed, which results in the pressure rising inside the ram chamber of the cylinder.

Types of Hydraulic Jacks

Two popular types of hydraulic jacks are bottle jacks and floor jacks. They are discussed here below: 

Bottle Jacks

Bottle jacks gained popularity during the first half of the 1900s as the automotive industry grew. Also known as hand jacks, bottle jacks offered a convenient means for a person to raise a car for roadside inspections or service. The hydraulic bottle’s design looks like a milk bottle’s shape, giving them its name. Today they vary in size and lifting capacities between one hundred pounds and several tons. So what exactly does a bottle jack operate? Bottle jacks have an incline that is vertical and is supported by an elevated platform (called a bearing pad) which directly supports an object’s load when the bottle is lifted.

Bottle Jacks
Image Source: Amazon

Although they are primarily used in the auto industry (1.5 to 5 tons jacks are the most common range of capacities used to lift vehicles), bottle jacks also have other applications. In the medical sector, they are used in stretchers made of hydraulic fluid or patient lifts. In industrial settings, they are used as pipe benders in plumbing, cable slicers used for electrical projects, and material lifts inside warehouses. Their capacity to lift loads is crucial in maintaining large agricultural machines and many construction processes. Bottle jacks can be secured to a frame or on beams or put up on their own the possibility of repositioning when necessary.

Floor Jacks

What exactly is a floor jack? In contrast to shafts for bottle jacks that work horizontally, the shaft of the floor jack operates horizontally. The shaft is driven by an engine connected to a pad for lifting, which is then lifted vertically. Floor jacks generally offer more lifting vertically than bottle jacks and come in two dimensions. The first jack was four feet long, a foot wide, and weighed 200 pounds. They can lift 4-10 tons. A smaller model was made later and is three feet in length and can lift 1 1/2 tons. While “mini jacks” are also made, they aren’t an official kind for floor jacks. Generally, one of the two sizes above is the one to be utilized.

Floor Jack
Image Source: Amazon

Other Types of Jacks

Toe Lift Hydraulic Jacks

Toe-lift hydraulic jacks are special hydraulic jacks that can be used to lift machines and other heavy loads when the space between the floor and the bottom of the weight is very low. This particular kind of jack can be used in cases where a bottle jack or floor jack cannot function due to the limited clearance between the ground and the bottom that the loads have.

Toe Lift Hydraulic Jacks
Image Source: Amazon

Leveling Jacks

Leveling Jacks employ mechanical screw mechanisms and are portable, frequently used to level RVs, trailers, and similar vehicles.

Scissor Jacks

Scissor jacks are devices that utilize an electronic screw whose movement causes the raising or lower of the scissoring arms that retract or extend depending on the angle of the screw’s mechanism.

Scissor Jacks
Image Source: Amazon

Screw Jacks

Screw Jacks are jacks with a mechanical design that uses the vertical screw mechanism to lift or lower the height of the jack. Some models are adjustable with a wrench, while others utilize a level through the hole of the jack to provide the use of mechanical advantage in turning the screw to lift the load.

Screw Jacks
Image Source: Amazon

Ratchet Jacks

Ratchet Jacks utilize the ratchet and pawl mechanism to lift or raise the weight. In the past, they were the standard kind of jack that auto manufacturers fitted with their vehicles to allow owners to use for changing the flat tire. The jack was placed to be attached to the car’s rear or front bumpers, and the tire wrench, which functioned as the handle for the jack and a wrench for lug nuts. However, as the unibody concept developed, construction, and the demise of bumpers made of metal on cars, the ratchet jacks were pushed out of their use. They were replaced by scissor-jacks, slimmer that allowed them to slide under the unibody to gain access to designated lift points.

Ratchet Jack
Image Source: Rotary Cutter Supply

Hydraulic Cylinder Failure Mechanisms and Causes

The hydraulic cylinders in jacks coul, requiring quite a cylinder repair or service to bring the jack back in a safe working condition. The most common causes of failure for hydraulic cylinders are:

  • Fluid contamination in the hydraulic system could cause particles to scratch or harm the cylinder, or the pollution of the hydraulic fluid could result in the deterioration or degradation of hydraulic seals.
  • Seal leakage causes the loss of pressure in the cylinder and a reduction in the capacities of the jack and could continue to increase over time and get more noticeable if seals are not replaced.
  • Side-loading impacts, in which the force vector used to determine applying the load on the cylinder is a part that isn’t parallel to an axis of the cylinder.
  • The inability to maintain an appropriate pressure inside the cylinder could increase the risk of leakage through seals.
  • Incorrect maintenance, in which the hydraulic cylinder wasn’t provided with regular inspections and maintenance recommendations, resulted in an increase in the service life and eventual failure of the device.
Hydraulic Cylinder
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Applications for Jacks

Jacks can be found across a variety of industries. They are utilized to move and lift massive loads to remove the vertical force of weight-bearing members to allow repairs to be made. They are valuable equipment for construction, shipbuilding, automotive repair, and other industries requiring specialized equipment. Some of the uses of jacks are:

  • Aircraft
  • Automotive, For example, to test the transmission as well as engine tests
  • Bridges
  • Cable tensioning
  • Construction
  • House shifting
  • General Industrial
  • Laboratory
  • Locomotive
  • Marine
  • Mobile Home
  • Railroad
  • Shipbuilding
  • Shoring and stabilizing like for mines and tunnels
  • Tractors & Trailers
Applications for Jacks
Image Source: ResearchGate

Specifications for Jacks and Hydraulic Jacks

Hydraulic jacks, as well as hydraulic jacks, are usually specified in a variety of essential specifications that are listed below. However, it is important to note that these parameters could vary depending on the type of jack used and can also differ from manufacturer to manufacturer.

  • Capacity is the highest weight the jack can lift, typically expressed in pounds or tons.
  • Maximum lift height is the biggest amount of distance or the displacement of the jack’s main ram or lift pad when it is fully extended, measured against the ground or to a reference surface.
  • The travel length is the time the ram lift pad will change from its extended position to a fully extended position.
  • The working orientation indicates the usage orientation of the jack (vertical or horizontal) following what is designed for the device.
  • Handle length is the total measurement of the length used for lifting and the length for lowering the jack.
  • The power source is the mechanism through which the jack is operated, for example, manually, air or pneumatic battery, electric, for instance.


Hydraulic jacks can lift massive loads, but they require maintenance to avoid the development of issues in the hydraulic parts, which could pose a risk to operators, for instance, issues with the cylinders, which aid in producing the force for lifting.

This article provides information about Jacks, with a concentration on hydraulic Jacks. For more information on other kinds of lifting mechanisms, refer to our article on lifting, or go to our Thomas Supplier Discovery Platform to discover similar suppliers of lifts, hydraulic jacks, or repair of cylinders.

Mia A Chloe
Author: Mia A Chloe

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