Hydraulic Systems: Principles, Components, and Benefits
Advantages of Hydraulic Systems
- Easy Speed Regulation: Oil, being an incompressible fluid, allows for easy and accurate speed variation in hydraulic or oleohydraulic actuators.
- Transmission of High Power: These systems enable the transmission of greater power per unit volume, achieving high-performance transmission.
- Precise Position Control: Thanks to the fluid’s incompressibility, an actuator can stop at any position with a high degree of accuracy.
- Reversibility of Actuators: The direction of rotation or movement can be instantly reversed via a suitable valve or pump.
- Protection System: Unlike mechanical transmissions where overload can cause breakdown, a hydraulic or oleohydraulic safety valve prevents overpressures that could lead to damage.
- Loading Capability on Startup and Shutdown: Enables the blocking of any sudden movement and allows for loading after startup.
Hydraulic System Characteristics
- Response:
- Fast / Slow
- Strength:
- Small / Large
- Weight:
- Light / Heavy
- Position Control:
- Difficult / Possible
- Speed Control:
- Inadequate / Adequate
- Supply Pressure:
- Low / High
- Stiffness of Intermediate Position:
- Low / High
- Drive System:
- Simple / Complex
- Price:
- Low / High
Fundamental Principles of Hydraulics
Pascal’s Principle and the Principle of Balance
Pascal’s Principle states that pressure at a point in an incompressible fluid at rest is transmitted equally in all directions throughout the liquid mass. The Principle of Balance states that, assuming no losses, this pressure is transmitted along the pipe. This can be expressed as: P1 = P2 => F1/A1 = F2/A2.
Thus, we conclude that a small force can generate a much larger force.
Hydraulic Pump Features
- Pressure: This is the nominal value of the maximum continuous working pressure for a given speed.
- Flow: Also known as geometric displacement, it is the volume of liquid pumped in a full revolution.
- Performance: The volumetric performance is the relationship between theoretical flow and actual flow, which typically ranges between 0.89 and 0.99, depending on various features. The total performance is the product of its volumetric and mechanical performance, ranging between 0.5 and 0.9.
Types of Hydrostatic Pumps
These pumps increase pressure.
- External Gear Rotary Pumps: Flow occurs as fluid is transported between the teeth of two fully meshed gears. One gear is driven by the motor, which in turn spins the other. This type of pump is commonly used in most oleohydraulic installations and is less sensitive to contaminants.
- Rotary Vane Pumps: Available with fixed or variable flow, they operate at low pressure. Their operation is based on a rotor housing mobile vanes that rotate within a ring. The pump forms a chamber between the rotor and its housing.
- Rotary Piston Pumps: These pumps have multiple piston-cylinder sets. The mechanism revolves around a motor shaft. There are two types of piston pumps: axial piston and radial piston. These pumps provide higher working pressures and a greater variety of flows than gear or vane pumps, offering the highest yield.
Common Hydraulic Valves
- Anti-Return Valve
- 4/3-Way Directional Control Valve
- 4/2-Way Directional Control Valve
- Pressure Regulating (Safety) Valve
- 2/2-Way Directional Control Valve