Principle of Hydraulics
The basic principle of hydraulics used for tool operation can be compared with a typical rotary car-wash brush tool, that is operated from water through a garden hose. Water rushing through the garden hose drives a small motor in the car-wash tool which, in turn, rotates the brush. However, it is not just the rushing water that is driving the motor. There is also pressure associated with the rushing water—about 60 pounds per square inch (psi). Without the pressure, the tool would have no power. Without pressure, any force applied to the tool, such as pushing down on the tool, would stall the tool. Water rushing through the hose (or the flow of water) is measured in gallons per minute (gpm) and results in the speed of the tool (in the case of the car-wash tool, the speed of the brush). Pressure associated with the water provides power to the tool.
The same principle applies in one of our tools. In a breaker, for example, the flow results in the speed of the tool and the resistance to that flow creates a demand for pressure. If the system has the capacity to deliver the pressure, power is transmitted to the tool to do work. Hydraulic tools actually use less flow (gpm) than that produced through a garden hose. The pressure, however, is considerably higher. Hydraulic tools require pressures up to 2000 psi / 140 bar but only need 5 to 10 gpm to operate effectively. A typical HTMA hydraulic system returns fluid to a reservoir for re-use as opposed to the car-wash brush tool that spills fluid to waste.
In pictures, the priciple of hydraulics looks like this:
Pressure exerted on a fluid is distributed equally throughout the fluid (Pascal's Principle). Hydraulics uses incompresible liquids so the applied pressure from one end (smaller arrow) is equal to the desired pressure on the other end (bigger arrow). The bigger arrow is pointing towards a piston that is free to move (it can also be connected to a rod). When the force is applied, the piston moves up and down.