Hydraulic System Components: Functions and Principles

Oil Tank Functions and Design

The oil tank, or reservoir, serves several critical functions in a hydraulic system.

Key Objectives of an Oil Tank

• Store System Fluid: To provide an adequate supply of hydraulic fluid for the system.
• Contaminant Settlement: To allow contaminants in suspension to settle out of the fluid.
• Temperature Regulation: To help maintain the fluid temperature within desired limits by dissipating heat.
• Air Dissipation: To facilitate the release of dissolved air or foam from the fluid.

Baffle Positioning in Oil Tanks

The position of baffles inside the tank is very important. Firstly, they establish separation between the suction line and the return line, preventing aerated or contaminated return oil from being immediately drawn back into the system. Secondly, the heat radiation capacity of the tank can be increased if baffles are positioned to ensure oil circulates along the outer walls, enhancing cooling.

Hydraulic Filters and Filtration

To maintain system cleanliness and protect sensitive components, filters and strainers are essential. Porous filters often utilize sieves with a metal mesh, providing a coarser level of filtration compared to other types. Most pumps are protected by a suction filter (strainer) designed to retain coarse solid particles, preventing them from entering the pump.

Filter Locations in Hydraulic Systems

Suction Line Filters

These filters, often strainers, are placed on the pump's suction line and typically offer lower filtration finesse (i.e., they capture larger particles).

Pressure Line Filters

Located after the pump, these filters are designed for finer filtration than suction line filters, protecting components downstream from contaminants generated or missed by the pump.

Relief Line Filters

Filtering the flow through a relief valve is an ideal arrangement, especially when flow control valves operate in series and excess flow is continuously directed to the tank via the relief valve. This ensures that oil passing through the relief valve is cleaned.

Return Line Filters

Oil returning from the system to the tank can pass through a filter. This is a common location to capture contaminants generated throughout the system before the oil re-enters the reservoir.

Hydraulic System Piping

Piping connects the various components of a hydraulic system, allowing fluid to flow between them. This includes:

• Main pressure lines: Carry fluid from the pump to actuators and control valves.
• Secondary lines: Branch off main lines for specific functions.
• Service lines: Used for auxiliary functions or connections.
• Return lines: Carry fluid back to the tank from actuators and valves.

Hydraulic Accumulators: Function and Uses

The primary function of a hydraulic accumulator is to store a specific amount of fluid under pressure, releasing it back into the system when needed.

Common Applications

• Emergency Fluid Reserve: Provides fluid pressure in case of pump failure.
• Leakage Compensation: Makes up for small internal or external leaks.
• Volume Compensation: Accommodates changes in fluid volume due to temperature variations.
• Elimination of Peak Pressures: Dampens pressure spikes and hydraulic shock.

Accumulator Types

• Bladder
• Piston
• Diaphragm

Pressure Relief Valves Explained

A pressure relief valve is typically mounted on the pressure side, after the hydraulic pump. Its primary function is to limit the maximum pressure in the hydraulic system to a safe and acceptable level, protecting components from overpressure.

Hydraulic Actuators: Force and Motion

A hydraulic actuator is a component powered by fluid pressure, converting this hydraulic energy into mechanical force and motion. Actuators can be either linear (e.g., hydraulic cylinders) or rotary (e.g., hydraulic motors).

Understanding Pascal's Law

Pascal's Law is a fundamental principle in fluid mechanics. It states that pressure exerted anywhere in a confined incompressible fluid is transmitted equally in all directions throughout the fluid and acts at right angles to the surfaces of the container.

Key Hydraulic System Components

I. Supply Elements

• Hydraulic Pump: Converts mechanical energy into hydraulic energy, creating fluid flow.
• Tank (Reservoir): Stores hydraulic fluid, facilitates cooling, and allows for contaminant settling and air separation.

Pump Types

Common types of hydraulic pumps include internal gear pumps and lobe pumps, among others.

II. Control Elements

A. Processors (Valves & Relays)

• Directional Control Valves: Direct the path of fluid flow to control the start, stop, and direction of actuators.
• Limit Relays: Electromechanical devices often used in control circuits, potentially triggered by limit switches.
• End-of-Stroke Pressure Valves (Sequence Valves): Control the sequence of operations based on pressure signals, often at the end of an actuator's stroke.
• Throttle Valves (Flow Control Valves): Regulate the speed of actuators by controlling the fluid flow rate.

B. Sensors & Input Devices

• Limit Switches: Detect the presence or position of machine parts.
• Buttons: Manual input devices for system control.
• Proximity Detectors: Non-contact sensors that detect the presence of objects.

C. Other Control Components

• Relays: Electrically operated switches used for control logic.
• Shuttle Valves: Allow flow from one of two inlet sources to a common outlet, blocking flow to the other inlet.

III. Output Elements (Actuators)

• Hydraulic Cylinders: Convert hydraulic energy into linear mechanical force and motion.
• Hydraulic Motors: Convert hydraulic energy into rotary mechanical force and motion.

Primary Types of Control Valves

Valves are crucial for controlling the hydraulic system. Key types include:

• Distributor Valves (Válvulas Distribuidoras / Directional Control Valves): Direct the flow of hydraulic fluid to different parts of the circuit.
• Shut-off Valves (Válvulas de Cierre): Stop or allow fluid flow in a line.
• Pressure Control Valves (Válvulas de Presión): Regulate or limit pressure in the system (e.g., relief valves, reducing valves, sequence valves).
• Throttle Valves (Válvulas de Estrangulación / Flow Control Valves): Control the flow rate of the fluid, thereby influencing actuator speed.