The hydraulic jack is a device used for lifting heavy loads by the application of much smaller force. It is based on Pascal’s law, which states that intensity of pressure is transmitted equally in all directions through a mass of fluid at rest.
Hydraulic jack is fluid filled. They work quick manually or electrically. They do not require much work to use manually. The downside is maintenance is required. If you use a hydraulic jack to work on a vehicle, jack stands are a MUST. Seal failures can cause a vehicle on a jack to drop without warning. This type of jack also requires more storage space and can be quite heavy.
Screw jacks require lots of manual work to operate. If used within it’s weight range, this kind of jack can be as safe as a jack stand. These jacks can be quite small and light, thus are the jack of choice for the automotive industry to install in all new cars for spare tire replacement
The working principle of a hydraulic jack may be explained by an example Consider a ram and plunger, operating in two cylinders of different diameters, which are interconnected at the bottom, through a chamber, which is filled with some liquid.
Hydraulic jack is typically used for shop work, rather than as an emergency jack to be carried with the vehicle. Use of jacks not designed for a specific vehicle requires more than the usual care in selecting ground conditions, the jacking point on the vehicle, and to ensure stability when the jack is extended.
A hydraulic jack uses a fluid, which is incompressible, that is forced into a cylinder by a pump plunger. Oil is used since it is self lubricating and stable. When the plunger pulls back, it draws oil out of the reservoir through a suction check valve into the pump chamber. When the plunger moves forward, it pushes the oil through a discharge check valve into the cylinder. The suction valve ball is within the chamber and opens with each draw of the plunger. The discharge valve ball is outside the chamber and opens when the oil is pushed into the cylinder. At this point the suction ball within the chamber is forced shut and oil pressure builds in the cylinder.
Hydraulic jack is the use of gas, liquid booster principle, combined with the telescopic hydraulic cylinder designed by a new, compact hydraulic lifting equipment, air pneumatic horizontal hydraulic jack completely replace the manual operations, especially suitable for automotive, tractors and other transportation industries.
● It uses ‘incompressible’ fluid which results in a greater, more efficient & consistent work or power output. This is due to the fact that hydraulic fluid molecules are able to resist compression under heavy load hence minimal energy loss is experienced and work applied is directly transferred to the actuating surfaces.
● As opposed to pneumatic system which uses air, a leakage in a hydraulic system is easier to spot during ground maintenance operations.
● Hydraulic fluid operates very well in a very hot working environment, it is able to sustain its airworthiness viscosity, density & fluid temperature even if it subjected under extreme heat. This is specially important on aircraft structures that is abundant of hot working conditions during flight operations.
● Hydraulic fluid is highly corrosive to most of the aircraft materials.
● Due to the heavy loads experienced in a typical hydraulic system, structural integrity is a must which also means higher structural weight for the aircraft in addition to the weight of its hydraulic lines, pumps, reservoirs, filters, & etc.
● Hydraulic system is susceptible to contaminations & foreign object damage (FOD).
● Mishandling and constant exposure to hydraulic fluid and its gas fumes without proper equipment and precautions is a health risk.
● If disposed improperly, a hydraulic fluid is an environmental risk.