A two post hoist is a device that can lift heavy loads using a hydraulic or electric motor and two sets of hoist arms. These hoists consist of two tower structures, which are typically referred to as posts. Each post contains a cable, chain, screw drive, or piston that is connected to a set of hoist arms. When the motor is activated, the lift device is used to pull the hoist arms off the ground and subsequently raise up a load. These hoists are typically used in automotive applications as an alternative to in-ground cartridge type hoists and four post platform hoists.
The most commonly used type of lifting device in the automotive field is the two post hoist, which accounts for about 85% of all car and truck lifts. These lifts are versatile and come in a variety of different configurations to suit different situations. The main types of two post hoists are hydraulic and electric, though a combination of the two is also popular. Purely electric two post hoists are popular in Europe, where the lift mechanism often uses a screw drive. Electric-hydraulic units use an electric motor to generate the necessary fluid pressure to operate the lift mechanism, unlike purely hydraulic units that usually use compressed air.
One common feature that most two post hoist units with electric-hydraulic drives share is equalization cables. These cables are designed to ensure that the hoist arms on each side raise at roughly the same time by connecting the lifting mechanism in one tower to the corresponding mechanism in the other. It is possible for these cables to pass from one post to the other at either the top or the bottom, depending on the design. If the equalization cables and hydraulic lines pass from the bottom of one post to the other, some type of skid plate is usually placed over them to prevent damage.
A two post hoist may also be either symmetric or asymmetric, which refers to the placement of the arms and the way that a load is situated on the hoist. Symmetric two post hoists have hoist arms that are the same length, so any load will tend to be centered in relationship to the towers. An asymmetric two post hoist typically has shorter front arms, which results in more of the load being situated on one side of the towers than the other. This can be desirable when lifting certain loads, such as automobiles, that are substantially heavier in the front than in the rear. Symmetric hoists are also useful for lifting vehicles in certain circumstances, such as those with especially long wheel bases.