Pascal’s Law
Blaise Pascal generated the law of hydraulics in the 17th century. Pascal’s law means that when pressure is placed on a fluid, the pressure is pushed equally throughout all areas. Pascal discovered that the weight of a piston with a small diameter size would balance the piston of a larger diameter size. Pascal had two pistons separated by liquid. When he added 100 pounds per square inch (689 kPa) on the small one-inch (2.5-cm) piston, it equated to five times that amount on the larger, five-inch (13-cm) diameter piston, creating a force of 500 pounds per square inch (3,447 kPa).
He determined an equation for hydraulics: the distance that the large piston moves in inches will be determined by the force of the small piston in pounds multiplied by the distance the small piston moves in inches, divided by the force of the larger piston in pounds.
 “On the Measurement of Running Waters”
Benedetto Castelli, a professor of mathematics in Italy, contributed to the idea of hydraulics in his book “On the Measurement of Running Waters.” His book, published in 1628, is said to have increased our knowledge of the process of hydraulics.
Hydraulics has been slowly seeping into the construction equipment industry since its discovery. The earliest recorded hydraulic shovel appeared in 1882 by Sir W.G. Armstrong & Co., a British company that used to build hull docks. Unrelated Armstrongs also built two water hydraulic shovels.
The use of hydraulics in machinery became more widespread after World War II. One of the first machines developed was the hydraulic excavator, which came as early as 1948 when Carlo and Mario Bruneri produced a wheeled prototype excavator. They gave up the patent and manufacture rights to a French company named SICAM in 1954, the same year they built Yumbo. The Yumbo, an S25 excavator, had a truck mounted on it.
The very first hydraulic excavator, the TU, was produced in 1951 with the help of Poclain. The excavator could not produce a full swing and the hydraulic power was achieved with the help of a pump. Poclain introduced the TY45, the first machine to revolve, in 1960. Since hydraulic excavators arrived on the horizon, they have made cable-operated machines almost obsolete.
Forklifts utilize the hydraulic system for its mast and wheel movements. The mast, which is responsible for lifting, lowering, and tilting the materials that it carries, is operated with hydraulic cylinders and rails that interlock to allow for the lifting/lowering operations.
Hydraulics is considered one of the best advancements within the skidder (or most machines in the industry). Hydraulics meant easier and more advanced control of the skidder and no leaks. The O-ring made hydraulics the more sophisticated option and provided tighter hoses for better use. Grapple skidders can have a hydraulic claw instead of a winch, or they can have a secondary hydraulic system that allows it to lift the claw to the rear of the machine as well as the lowering motion. Some skidders can even swing the trees from side to side.
These are just a few of the advantages and uses for hydraulics in the construction equipment industry.
 How it Works
Hydraulics operates by transmitting force via a near compressible fluid, usually oil. When an operator pulls a lever or presses a control button that force is pushed into a cylinder by a piston and creates an action. It is similar to pneumatics with the exception that it uses liquid and not air.
Oil is the liquid of choice because it contains characteristics that enable it to maintain the same volume even when a piston is pushed. Oil enables force to be exerted from one piston to another with an impact that is almost fully realized.
The use of hydraulics is convenient because different measurements of force can be applied and different targets of the force can easily be created. For example, on a hydraulic truck crane, there is a hydraulic cylinder that controls the force being exerted to lift heavy weights, and at the same time, the hydraulic pumps can control the brake and gas pedals on the machine. Another way to look at this is the brakes in a car: a master cylinder links to four slave pistons by oil traveling down tubes or pipes. When the master cylinder is pushed, the force is exerted into the four cylinders to enable the car to brake. This is common with most machine types.
Hydraulic systems require a lot of oil. It is said that 100 gallons (379 L) of oil is typical of a machine running on six to eight cylinders. The system must also have large external reservoirs to store the oil that is being displaced by the cylinder(s).
- Hydraulics. Sweethaven. 2008-09-29.
- Benedetto Castelli. Connexions. 2008-09-28.
- Haddock, Keith. The Earthmover Encylopedia. Motorbooks: St. Paul, 2002. 225-263.
- Drushka, Ken and Konttinen, Hannu. Tracks in the Forest. Timberjack Group: Helsinki: 1996.
- Hydraulic. Howsstuffworks.com. 2008-09-29.