Lifting Jacks Information
Lifting jacks are used for leveling or positioning heavy equipment, lifting automobiles and for supporting structures. They typically use screw or cylinder-based actuators and are powered by hydraulic, mechanical, electric, or manual methods. The lifting element is described as either a shoe or a saddle. A shoe is usually specially designed to match a lifting point while a saddle is a plate that is made to lift on many places.
Lifting jacks are a basic tool of industry and are especially common in automotive applications. Lifting a car with its stock lifting jack to change a tire is the most common application. Other uses include:
- Raising and leveling steel girders on their footings or vertical columns
- Leveling and positioning heavy machinery in a machine shop or manufacturing facility
- Lifting and positioning heavy pieces of metal stock or other materials
There are multitudes of uses where heavy objects have to be raised using some basic mechanic principle such as hydraulic, pneumatic, inclined plane or mechanical screw. This is where long distance acting on a light force translates into lifting up a heavy force up a short distance.
Safety Note: When using a lifting jack to lift any sort of heavy vehicle or workpiece, always use stands or supports underneath to hold the load in place in case the jack fails.
There are many different types of lifting jacks including bottle jacks, floor jacks, ratchet jacks, scissor jacks, screw jacks, transmission jacks and others.
These are simple hydraulic lever jacks that use a mechanical advantage of high pressure small diameter piston, or the master, pumping fluid into a large diameter piston’s chamber or the slave cylinder. The two are mounted next to each other on the base. The master is usually pumped up and down by a simple lever that often doubles as the wrench that operates the release valve. They have a simple round saddle on top and a rectangular cast iron base. They are used mainly for vehicles but they have many applications otherwise, being so simple and small. The main disadvantage is that they must be used standing upright, not on its side or the pumping action won’t work correctly.
House jacks, as per its name, are super heavy duty jacks that are used to raise or stabilize a whole house or heavy beams. They usually employ the screw or bottle jack lifting principle and can be provided with or without thrust bearings.
These are air powered jacks that are run off of a shop compressed air system. They have the advantage of a very low minimum height and high lifting capacity. Disadvantages include being more prone to air leakage and thus have to have a safety system built in to prevent rapid unwanted lowering due to bag failure.
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.
These are simple jacks that have four linked vertical arms. Between each of the two pairs of vertical arms there is a female threaded piece where the jack’s screw goes through. The jack is raised or lowered by rotating the operating screw. These are usually found in a car trunk as a tire changing tool due to its compact size. Scissor jacks provide by automobile manufacturers generally have a shoe to mate to a lifting point in the vehicle’s frame, while the universal aftermarket versions have a generic saddle instead.
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.
Service or Floor Jacks
These are the workhorses of the vehicle repair world, noted and prized for their safety, strength, convenience and capacity. They work on a similar principle as a bottle jack, but they are mounted on a 4 or 6 wheeled carriages that have swivel castors in the rear and fixed cast wheels in the front. They have a large round saddle that can be removed easily and replaced with different sizes or custom saddles and shoes. The pump lever is also the way you pull and move the jack around. The lever also acts as its release valve actuator by rotating the handle. Floor jacks have a low initial clearance so they can get under a low car then safely jack it up.
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.
Wheel and Shop Bumper Jacks
These are large roll around floor jacks that can lift a whole vehicle up by the front or the rear by cradling the wheels or pushing up on the front of the frame. They have a floor carriage and a large vertical gantry that holds the piston. They are usually hydraulic powered and are popular in small repair shops where a built-in lift is too expensive.
Important specifications for lifting jacks include:
- Load or lift capacity
- Stroke or lifting height
- Minimum height
- Maximum height
- Type of jack: scissors, ratchet, screw, etc.
- Power source: hand, pneumatic, hydraulic, electric
- Safety locks and stops