What is Hydraulic Jack | Work, Type, Application

 What is a Hydraulic Jack?

A hydraulic jack is a device that is used to lift heavy loads by applying a force via a hydraulic cylinder with the help of hydraulic fluid. Hydraulic jacks lift loads using the force created by the pressure in the cylinder or barrel  chamber. 

A hydraulic jack creates pressure by moving hydraulic oil through two cylinders via a pump plunger. When the pump plunger is drawn back, it opens the suction valve and draws oil into the pump chamber. As the plunger is pushed down, the oil is transported through an external discharge valve and into the large cylinder chamber. Now the suction valve close, and pressure being built up in the chamber; causing the piston in the chamber to rise and lift heavy object. This process can be repeated many times, allowing load to be lifted higher, and higher.

Hydraulic jacks function based on a concept in fluid mechanics known as Pascal’s laws. Essentially, if two cylinders (a large cylinder 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 transfer to the second cylinder through the fluid connecting them. However, 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.

Equation for Pascal’s Principle.

                                           F1/A1 = F2/A2

where:

F1 is the applied force to piston 1

A1 is the area of piston 1

F2 is the applied force to piston 2

A2 is the area of piston 2

then

                                        F2 = F1(A2/A1)

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 principle to lift heavy loads: they use plungers to move oil through two cylinders. First plunger is drawn back, which opens the suction valve ball within and draws oil into the pump or vessel chamber. When 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 or large cylinder.

Type of Hydraulic Jack

•        Bottle jack –  Bottle jacks use a shaft which is vertical, and supports a bearing pad that directly holds the weight of the load as it’s lifted.
•       Trolley/Floor jack –  These jacks provide a much greater range capacity of vertical lift than bottle jacks and available in two main sizes – small size and large size.

Applications for Hydraulic Jacks

Hydraulic 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. 

Hydraulic Jacks used in 

1. Aircraft
2. Automotive, such as for transmissions and engine testing
3. Bridges
4. Cable tensioning
5. Construction
6. House moving
7. General Industrial
8. Locomotive
9. Marines
10. Mobile Home
11. Railroad
12. Shipbuilding
13. Tractors & Trailers