An Introduction to Types Of Lifting Jacks , Applications And Calculation

 An Introduction to Types Of lifting Jacks , Applications And Calculation

Introduction

A jack is a device that uses force to lift heavy loads. The primary mechanism with which force is applied varies, depending on the specific type of jack, but is typically a screw thread or a hydraulic cylinder. Jacks can be categorized based on the type of force they employ: mechanical or hydraulic. 

Jack types by force used

There three main jacks

Mechanical jacks

such as car jacks and house jacks, lift heavy equipment and are rated based on lifting capacity

Hydraulic jacks

Hydraulic jack tend to be stronger and can lift heavier loads higher, and include bottle jacks and floor jacks. HYDRAULIC JACKS depend on force generated by pressure

Pneumatic jacks

Pneumatic jacks are powered by compressed air and are used for lifting and positioning heavy material and machinery effortlessly. Pneumatic power turns electric power into mechanical power with the help of compressed air. The compressed air transfers the force for the purpose of lifting, pushing, or moving of heavy components.

Jack types by actuation
Hand

Foot
Air / Pneumatic
Hydraulic
Electric Motor

working principle

hydraulic  jacks

The hydraulic jack is based on the Pascal principle, that is, the pressure across the liquid is the same. In a balanced system, the pressure on the smaller piston is smaller, and the pressure on the larger piston is larger. Therefore, through the transmission of liquid, different pressures at different ends can be obtained, so as to achieve the purpose of transformation.

Mechanical jacks

The mechanical jack uses the mechanical principle to reciprocate the handle to push the ratchet wheel to rotate. The small bevel gear drives the large bevel gear and rotates the weight lifting screw, so that the lifting sleeve can be lifted or lowered to achieve the function of lifting tension.

FIG 1

Mechanical jacks 

A jack is a mechanical lifting device used to apply great forces or lift heavy loads. A mechanical jack employs a screw thread for lifting heavy equipment.

Scissor jack

Scissor car jacks usually use mechanical advantage to allow a human to lift a vehicle by manual force alone. The jack shown at the down is made for a modern vehicle and the notch fits into a jack-up point on a uni body. Earlier versions have a platform to lift on a vehicle's frame or axle.

FIG 2

Electrically operated car scissor jacks are powered by 12 volt electricity supplied directly from the car's cigarette lighter receptacle. The electrical energy is used to power these car jacks to raise and lower automatically. Electric jacks require less effort from the motorist for operation.

FIG 3

Screw Jack

This is a very common and simple sort of jack. It operates under the principle of using the mechanical advantage of the basic screw thread to convert the rotary motion of the wrench or lever into the linear motion of the top of the jack. The mechanical advantage is directly related to the pitch of the screw. Most refrigerators and free standing stoves have simple screw jacks as the floor pads of the unit. The user can easily level the unit off by using a simple open end wrench. More complicated versions of screw jacks are found in machine shops to level out heavy machine tools. Often a locator hole is drilled in the floor or table to keep the jack’s bottom in position and from slipping. More advanced versions have ball bearings between the screw and its tapped hole to reduce friction.

FIG 4

Are suitable for house movers, leveling, supporting, shop and factory maintenance, riggers, locomotive repairs, drillers and farm applications. Malleable housings are lighter and unbreakable

Ratchet Jacks

Ratchet jacks use the ratchet and pawl mechanism that cause a rotary gear to move up or down a linear track. The ratchet pawls keep the gear from slipping back down under load and causing the jack to fail. The old traditional bumper jack in older American cars was a ratchet style jack. But they are not very safe and are heavy. So for those reasons they have been superseded by scissor jacks as standard equipment on most vehicles. They are still used in industry for lifting lighter pieces.

FIG 5

Are ideal for mills and factory maintenance, oil fields, shipyards, farms, machinery riggers, construction contactors, mining operators, bridge and rail car repair and heavy-duty industrial maintenance. These are the most versatile, general-purpose jacks available. Rugged construction permits safe, efficient lifting, lowering, skidding, moving, sustaining and leveling

Pushing Jack - Pull jack

Hand operated pulling jack with pulling eyes at each end. Pumping action turns gears to retract piston. Jack may be used for pulling and pushing. Internal pulling mechanism is made from chrome molybdenum (chromemoly) steel to withstand excessive loads. Gear construction provides strong and precise interlocking feature for no creeping under load and smooth pulling.

FIG 6

Are used for pulling or pushing of heavy objects. Ideal for applications where electric or hydraulic power is inconvenient or dangerous.

Trench Braces & Roof Supports

Are designed for putting up cross timbers and steel beams, aligning steel mine cars, a temporary prop in connection with loading equipment, pulling up and removing slack in power cables and pulling and pushing conveyor lines and controlling the tail piece.

FIG 7

Antique House jack

Are a mechanical device primarily used to lift buildings from their foundations for repairs or relocation. A series of jacks is used and then wood cribbing temporarily supports the structure. This process is repeated until the desired height is reached. The house jack can be used for jacking carrying beams that have settled or for installing new structural beams. On the top of the jack is a cast iron circular pad that the jacking post rests on. This pad moves independently of the house jack so that it does not turn as the acme-threaded rod is turned with a metal rod. This piece tilts very slightly, but not enough to render the post dangerously out of plumb.

FIG 8

Mechanical floor jack

Floor jack shaft is operated horizontally. When the handle pushes downwards the jack lift the car upward.The main advantages of Floor jack Is it can seat low to the ground and can operate speedy.

Mechanical floor jack is developed with screwing mechanism. Screw mechanism is used to lift the weight.

FIG 9

High-Lift Jack

They are constructed from strong, durable metals enabling them to lift heavy vehicles with relative ease. In general, high-lift jacks are rated up to 7,000 lbs while being able to lift up to 5 feet. However, high-lift jacks also weigh up to 30 lbs and are typically 3-5 feet in length meaning they're often not suitable for most vehicles.
They evenly distribute a load, even when the ground is soft or treacherous.
Lifting several thousands of pounds is easy and the operator exerts little physical effort.

High lift jacks can be used vertically or horizontally and are extremely versatile beyond regular vehicle maintenance and repair. They are useful tools for winching, spreading metal in the event of someone being trapped in a car accident, pulling and clamping heavy loads.

FIG 10

Hydraulic Jacks
Hydraulic jacks operate by applying pressure to one side of a hydraulic cylinder which in turn moves the jack head. Hydraulic jacks are lowered automatically by releasing the pressure on the cylinder. Vertical hydraulic jacks come in a variety of types, in capacities from 3 to 100 tons, and have different extended heights.

Bottle Jacks

A hydraulic jack is a powerful lifting or pushing tool designed to provide effective lift over greater distances than a basic mechanical jack. They are commonly used in workshops or onsite for specialised engineering applications. 

Hydraulic jacks operate by applying pressure to one side of a hydraulic cylinder which in turn moves the jack head. Hydraulic jacks are lowered automatically by releasing the pressure on the cylinder. Vertical hydraulic jacks come in a variety of types, in capacities from 3 to 100 tons, and have different extended heights.

FIG 11

Hydraulic floor jack

Hydraulic Floor Jack is designed to lift, but not support, one end of a vehicle. This Jack must be used in conjunction with a pair of appropriately rated jack stands

FIG 12

Transmission Jacks

These are specialty jacks used to raise and lower a vehicle’s transmission from the bottom of the vehicle. They are similar to a floor jack but have a large cradle with tie downs to secure the transmission and a way to tilt the transmission cradle so it can match the angle of the engine it will be bolted to. This allows the mechanic to raises the transmission into place for securing to the engine.

FIG 13

Porta power jack

It consists of a pump and ram connected by a hydraulic or oil hose. These jacks are rated at 3-, 7-, 20-, 30-, and 100-ton capacities and have many different applications.

The push-pull hydraulic jacks are furnished with an assortment of attachments that enable pushing, pulling, lifting, pressing, bending, spreading, and clamping operations. The pump is hand operated. The control valve on the side of the pump is simply turned clockwise, while the hand lever is stroked up and down to extend the ram. The flexible hydraulic or oil hose allows the user to operate the ram from a safe distance and in any desired position.

The ram retracts automatically by turning the control valve counterclockwise. The attachments can be threaded to the end of the plunger to the ram body or into the ram base.

FIG 14

Motorcycle jack

Usually motorcycle jacks are often used to lift the motorcycle for cleaning and modification. It is developed for lifting the motorcycle safely and also used for lifting ATV 4 wheel style vehicles.

FIG 15

strand jack

A strand jack can be considered a linear winch. In a strand jack, a bundle of steel cables or strands are guided through a hydraulic cylinder, above and below the cylinder are anchor systems with wedges that grip the strand bundle. By stroking the cylinder in and out while the grips are engaged in the anchors, a lifting or lowering movement is achieved.

FIG 16

Pneumatic jack

An air hydraulic jack is a hydraulic jack that is actuated by compressed air - for example, air from a compressor - instead of human work. This eliminates the need for the user to actuate the hydraulic mechanism, saving effort and potentially increasing speed. Sometimes, such jacks are also able to be operated by the normal hydraulic actuation method, thereby retaining functionality, even if a source of compressed air is not available.

Air frame jacks
are used for lifting an entire aircraft off the ground or deck. Airframe jacks are commonly called tripod jacks. The jacks may also be called wing, nose, fuselage, and tail jacks. These names come from the jack placement on the aircraft.

FIG 17

Inflatable jack

An inflatable jack, lifting bag, or pneumatic lifting bag is an air bag that is inflated by compressed air (without a hydraulic component) in order to lift objects. The bag can be deflated to be reused later. The objects can be of a smaller load such as an automobile or it can be a larger object such as an airplane.

Air bags are also used by rescuers to lift heavy objects up to help victims who are trapped under those objects. There are three main types of lifting bags for rescue: high pressure, medium pressure and low pressure systems. Low-pressure bags are operated at 7.25 psi for high vertical lift in a large surface area but lower lifting capacities. Medium-pressure bags are operated at 15 psi. High-pressure bags which have higher lifting capacities are operated at pressure between 90 and 145 psi. Two air bags can be stacked together to provide a higher lift. It is recommended that no more than two bags can be used in a stacked configuration, the bigger bag must be the bottom one, and no other objects are inserted between the stacked bags. Incorrect use of stacked bags may result in a bag (or other objects) shooting out to create a dangerous projectile

FIG 18

Mechanical jack effort calculation
A machine is a device that can change the magnitude and line of the action of force

FIG 19

A simple machine amplifies the input (effort) force to a larger output (load) force. The force ratio can be expressed as

Fr = F / S 

where
Fr = force ratio - mechanical advantage
F = load force (N, lbf)
S = effort force (N, lbf

FIG 20

The effort force for a screw jack when neglecting friction can be expressed as

F = (Q p) / (2 π R)

where
F = effort force at the end of the arm or handle (lb, N)
Q = weight or load (lb, N)
p = pitch - distance or lead of thread in one turn (in, m)
R = lever-arm radius (in, m)

The torque acting on the screw can be calculated as

T = F R 

where
T = torque (lb in, Nm)

Screw Jack with Friction

For motion in the same direction as the load (load assist the screw jack), the effort force can expressed as

F = Q ( (2 π μ r - p) / (2 π r + μ p) ) (r / R) 

where
r = pitch radius of screw (in)
μ = friction coefficient

For motion in the opposite direction as the load (load resists the screw jack), the effort force can expressed as

F = Q ( (2 π μ r + p) / (2 π r - μ p) ) (r / R)

 

Hydraulic jack effort calculation



Pascal's Laws relates to pressures in incompressible fluids - liquids.
-- if the weight of a fluid is neglected the pressure throughout an enclosed volume will be the same
-- the static pressure in a fluid acts equally in all directions
--the static pressure acts at right angles to any surface in contact with the fluid

Pressure in a Hydraulic Cylinder

The pressure  in an hydraulic cylinder acts equally on all surfaces. The force on a piston can be calculated

F = p A 

where
F = force (N)
p = pressure (Pa, N/m²)
A = area (m²)
The pressure acting on both pistons in a hydraulic jack is equal.

FIG 21

The force equation for the small cylinder:

Fs = p As 

where
Fs = force acting on the piston in the small cylinder (N)
As = area of small cylinder (m²)
p = pressure in small and large cylinder (Pa, N/m²)

The force equation for the large cylinder:

Fl = p Al 

where
Fl = force acting on the piston in the large cylinder (N)
Al = area of large cylinder (m²)
p = pressure in small and large cylinder (Pa, N/m²)

From previews  relations

Fs / As = Fl / Al 

or

Fs = Fl As / Al

 

Lifting jack selection considerations   

When choosing the right jack, the following should be considered
- What is to be lifted?
- The weight to be lifted
- The height required
- The space available to position the jack
- The required stability when the jack is extended
- How portable the jack needs to be?
- Whether the motive power will come from human effort or with compressed air (a pneumatic jack)
- Ease of servicing and maintenance

Main components of hydraulic and mechanical jacks

mechanical jacks
-Cup

-Screw and special washer

-Screw spindle (thread rod)

-Main nut

 -Body or  frame

FIG 22

Hydraulic jacks

-A reservoir
-Pumps
-Cylinder
-Piston
-Check valves or ball valves
-Release valve.

FIG 23

Care of Jacks

Use the following guidelines when working with jacks:
A- Keep fingers away from all moving parts.

B- Be aware of the capabilities of the jack, especially its load capacity.

C- Overloading can be hazardous to the jack, the operating personnel, and the load in event of jack failure.

D- Inspect all jacks prior to use.

E- Coat all surfaces with a thin film of light oil when not in use. When storing for long periods, apply a rust-preventive compound and store in a dry place.

F- Make certain that hydraulic jacks are filled with oil and that there are no visible oil leaks before use.

G- Periodically check the hydraulic fluid level in hydraulic jacks. Make sure the ram is in the retracted position when checking the level of oil and when filling.

H- Ratchet lever jacks should be well greased. A thin coat applied by hand or a brush is sufficient for all movable parts except the bushings. The bushings should be filled with grease in the small hole provided for greasing purposes. Keep rack sides and front greased, but do not grease the rack teeth.

I- When jacking up vehicles, make certain no one is under the vehicle to be raised. Set the hand brake firmly and block the front wheels if a rear wheel is being changed. Block the rear wheels if a front wheel is being changed. Place blocking or other supports under the vehicle when it is raised to the desired height to prevent it from dropping if the jack fails.