Hydraulic Oil Reservoirs: Functions, Classification, and Selection

Hydraulic systems play a vital role in many modern industries. And one of the indispensable components of this system is the hydraulic oil tank (reservoir).

A hydraulic oil reservoir is not merely a container for oil; it also performs many other critical functions that directly affect the performance and lifespan of the entire system. In this article, we will explore the hydraulic oil tank in detail, from its construction and operating principles to selection and maintenance.

What is a Hydraulic Oil Tank? Its Role in Hydraulic Systems

A hydraulic oil tank is an essential component in any hydraulic system. It is not just a storage tank; it plays a key role in ensuring stable, efficient operation and extending the lifespan of the entire system.

Key roles:

Fluid Storage: The reservoir has a capacity large enough to hold the fluid necessary for continuous system operation. The tank volume is calculated based on the hydraulic pump flow rate and the system’s operating cycle.

De-aeration: During operation, hydraulic oil may become entrained with air. Hydraulic oil basins are designed with baffles and de-aeration components to remove air bubbles, preventing cavitation which damages pumps, valves, and hydraulic cylinders.

Oil Cooling: Hydraulic fluid heats up due to friction during operation. The oil tank helps dissipate heat through the tank walls or via dedicated cooling units like fans or heat exchangers. Maintaining a stable oil temperature increases the life of the oil and hydraulic components.

Oil Filtration: Hydraulic oil reservoirs are usually equipped with filters to remove debris, metal particles, and other impurities, protecting system components from wear and damage. Oil filtration extends the life of hydraulic pumps, control valves, and cylinders.

Oil Monitoring: Oil tanks often feature sight glasses and oil level indicators (oil level sensors) so operators can easily check the quantity and quality of the oil in the system.

Refer more: What type of hydraulic oil do motorcycle lift tables use?

Types of Hydraulic Oil Reservoirs

Classification by capacity: Small, medium, and large capacity tanks.

Classification by material: Steel tanks, stainless steel (inox) tanks, and composite tanks.

Classification by application: Hydraulic oil tanks for forklifts, excavators, hydraulic presses, etc.

Detailed Construction

Tank Body: Made from steel, stainless steel, or composite, capable of withstanding pressure and resisting corrosion.

Tank Cover: Features airtight gaskets, air vents, and air filtration units.

Sight Glass: Used to check oil levels and quality.

Drain Valve: Used to drain oil when necessary.

Oil Filter: Return filters or suction filters to remove debris.

Oil Level Gauge: Displays the oil level inside the tank.

Cooling Unit: Air fan or heat exchanger.

Base Mount: Helps secure the oil tank in place.

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Operating Principle

Storage and Oil Supply Process

Storage: The reservoir serves as the storage for hydraulic oil for the entire system. The volume is calculated based on pump flow and operation time to ensure enough oil for continuous work.

Supply: The hydraulic pump sucks oil from the tank and pushes it to other components like hydraulic throttle valves, cylinders, and motors through hydraulic piping. After performing the transmission function, the fluid returns to the reservoir.

De-aeration and Cooling Mechanisms

De-aeration:

• Oil returning to the tank often carries air bubbles, which cause cavitation, reducing efficiency and damaging the system.
• The tank is designed to slow down the oil flow, allowing air bubbles to rise to the surface and escape through the air vent.
• Some reservoirs include internal baffles or separate de-aeration units to increase efficiency.

Cooling:

• Oil heats up due to friction. Excessive heat reduces the lifespan of the fluid and components.
• The tank dissipates heat by:

1. Natural dissipation: Heat is transferred through the tank walls to the surrounding environment.
2. Forced cooling: Using air fans or hydraulic oil heat exchangers to boost cooling efficiency.

The Role of Filters in System Protection

Oil Cleaning: Filters are installed in the tank (return filter) or on the piping (suction filter) to remove dirt, metal chips, and impurities.

Return Filter: Filters oil after it has passed through hydraulic components and returns to the tank, removing metal particles generated by friction.

Suction Filter: Filters oil before it enters the pump, protecting the pump from impurities.

System Protection: Clean oil reduces friction and wear, prevents clogging and damage to vital parts like pumps, control valves, and hydraulic cylinders, thereby extending system life.

Factors Affecting Hydraulic Oil Tank Efficiency

Reservoir Capacity

Reservoir capacity must be accurately calculated based on pump flow and system operation time.

Formula for tank capacity (reference): V = Q x T x K, where:

V: Tank capacity (liters)

Q: Pump flow rate (liters/minute)

T: Operating time (minutes)

K: Safety factor (usually 3 to 5)

Example: If pump flow is 10 L/min, operating time is 60 minutes, and the safety factor is 4, the required capacity is: V = 10 x 60 x 4 = 2400 liters.

Reservoir Design

Shape and size: Affects de-aeration and cooling capabilities.

Larger dimensions aid better heat dissipation.

Internal baffles help slow the flow, supporting air separation.

Air vent location and size: Ensure air bubbles escape effectively.

Ambient Temperature

Ambient temperature impacts cooling efficiency.

In high-temperature environments, cooling units (fans, heat exchangers) with appropriate capacity must be chosen to keep oil within the allowed range.

Example: Dock Levelers operating in high-heat environments need suitable oil coolers to ensure system longevity.

Filter Maintenance

Cleaning or replacing hydraulic filters periodically is crucial to maintaining filtration efficiency and protecting the system.

Dirty filters reduce oil flow, increase system pressure, and damage components.

Frequency depends on operating conditions and oil quality.

How to Choose the Right Hydraulic Oil Tank

Selecting the correct reservoir is vital for performance, durability, and safety. Here is a detailed guide from experts to help you choose the optimal tank:

Determine Capacity Based on Pump Flow

The tank must be large enough to hold the necessary fluid for operation.

This depends on pump flow, operating time, and the safety factor.

Capacity formula: (as mentioned previously)

Note: Consider the oil volume contained within actuators (hydraulic cylinders) and piping when calculating tank capacity.

Selecting Materials for the Work Environment

Tanks are made from carbon steel, stainless steel (inox), or composite.

Carbon steel: Affordable, durable, easy to fabricate, suitable for most applications.

Stainless steel (inox): High corrosion resistance, ideal for humid or chemical-heavy environments.

Composite: Lightweight, corrosion-resistant, good insulation, but higher cost.

Material choice should be based on environmental conditions (temp, humidity, chemicals) and requirements for durability.

Key Factors to Consider

Working Pressure: Choose a tank capable of withstanding the system’s maximum operating pressure.

Temperature: Consider both fluid and ambient temperatures to pick materials and cooling units.

Oil Viscosity: Select a design compatible with the viscosity of the hydraulic oil used.

Installation Location: Ensure the tank is placed for easy inspection, maintenance, and oil changes.

Available Space: Tank dimensions must fit the installation footprint.

Maintenance Requirements: Pick a design that is easy to clean.

Brand and Price: Opt for tanks from reputable brands with reasonable pricing.

Technical Standards: The tank must meet material, design, and safety standards.

Expert Consultation

If you are unsure how to choose, contact our experts for free advice.

An expert will help you define capacity, material, style, and specs suited to your specific system needs.

Applications of Hydraulic Oil Reservoirs

The oil tank is the foundation for operation in various industries and lifting equipment such as hydraulic lift tables, dock levelers, mobile yard ramps, and hydraulic goods lifts.

In Industrial Sectors

Mechanical Engineering: Widely used in metalworking machines like cutters, punch presses, mills, lathes, automated production lines, and industrial robots.

Construction: Essential for excavators, bulldozers, large cranes, mini cranes, piling rigs, and compactors, often combined with hydraulic lifts for material handling.

Mining: Used in tunnel drills, stone crushers, coal transport systems, and ore sifters.

Agriculture: Found in tractors, combine harvesters, pesticide sprayers, and plows.

Energy Industry: Used in hydroelectric and thermal power plants, and renewable systems like wind turbines and solar trackers.

Maritime: Applied in ships, port cargo lifting systems, and vessel control systems.

Manufacturing: Used in plastic injection machines, steel rolling mills, packaging machines, and food/pharmaceutical/paper production lines, especially systems using hydraulic lift tables.

In Specific Machinery

Hydraulic Lift Tables, Dock Levelers, Hydraulic Goods Lifts: The oil tank supplies fluid for these lifting systems to handle goods safely and efficiently.

Forklifts: Supplies oil for lifting, steering, and other functions. Forklifts often work with yard ramps for efficient loading/unloading.

Excavators: Supplies oil for operating buckets, booms, and travel motors.

Hydraulic Presses: Supplies fluid for the system generating pressing force.

Cranes: Supplies oil for hoisting, boom extension, and rotation.

Drills: Supplies oil for rotation and travel functions.

Example Illustration:

In a cargo lifting system using a hydraulic lift table: The tank supplies oil to the hydraulic cylinder to raise and lower the platform, moving goods between levels.

Maintenance and Repair of Hydraulic Oil Reservoirs

Proper maintenance is the key to ensuring system stability, efficiency, and longevity, while preventing unexpected failures. Here is a guide to the maintenance process:

Periodic Inspections

Oil Level:

• Check the fluid level frequently using a dipstick or oil level sensor.
• Ensure the level stays within the marked range on the tank.
• Top up when necessary using the correct recommended hydraulic oil.

Filter Condition:

• Check filters periodically (return and suction) for signs of clogging or damage.
• Clean or replace filters as per manufacturer recommendations.

Leaks:

• Thoroughly inspect joints, pipes, and seals for oil leaks.
• Fix leaks immediately to prevent fluid loss, environmental pollution, and equipment damage.

Periodic Cleaning and Oil Changes

Reservoir Cleaning:

• Clean the reservoir periodically to remove sediment and metal particles.
• Use dedicated cleaning solutions and tools to clean the tank.
• Frequency depends on operating conditions and environment.

Oil Changes:

• Change oil periodically based on manufacturer recommendations or actual conditions.
• Use oil suction equipment to remove old oil and pump in fresh fluid.
• Oil changes remove contaminants and oxidation products, maintaining system performance.

Handling Common Issues

Oil Leakage:

Identify the leak source and fix by replacing seals, tightening joints with wrenches, or replacing damaged hoses.

High Oil Temperature:

Check and clean cooling units (fans, heat exchangers), add coolant, or change the hydraulic oil if necessary.

Contaminated Oil:

Replace filters and clean the tank. Identify the source of contamination (e.g., water, dust) and rectify it.

Low Oil Level:

Add hydraulic fluid and investigate causes for loss (leaks, evaporation).

Tank Corrosion:

Clean and repaint the tank with anti-corrosive paint. If corrosion is severe, replace the tank.

Notes When Using Hydraulic Oil Reservoirs

To ensure operator safety and system efficiency, keep the following in mind:

General Notes

Regularly inspect and maintain the tank according to manufacturer instructions.

Record maintenance and oil change details to track system history.

Selecting the Right Hydraulic Oil

Use the fluid recommended by the equipment manufacturer. Hydraulic oils differ in viscosity, viscosity index, anti-wear, and anti-oxidation properties.

Using the wrong oil can cause damage and reduce performance.

Use high-quality oil with clear origins. Poor quality oil contains impurities that clog filters and wear down parts.

Before filling, verify the oil is clean and free of contamination or water.

Proper Operation Procedures

Before operation, check the oil level and start the pump at low pressure for a period to allow oil to circulate evenly.

Do not operate the system beyond allowed pressure and temperature limits.

Monitor oil temperature, system pressure, and listen for abnormal sounds to detect early issues.

After use, reduce system pressure before turning off the hydraulic pump.

Ensuring Occupational Safety

Use full protective gear (gloves, goggles, protective clothing) when handling hydraulic oil.

Hydraulic oil can cause burns on skin contact. Be careful during changes to avoid splashing.

Waste hydraulic oil is hazardous; collect and dispose of it properly to protect the environment.

No smoking or open flames near the hydraulic oil tank area.

Conclusion

The hydraulic oil tank is a vital component impacting system efficiency and life. Understanding its construction, function, and maintenance helps you operate safely, effectively, and cost-efficiently.

We hope this article has provided useful information. If you have questions or need further advice, please contact us.