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The Vital Role of the Hydraulic Oil Tank in Hydraulic Systems

A hydraulic oil tank, also known as a hydraulic fluid reservoir or hydraulic reservoir tank, plays a crucial role in the proper functioning and longevity of any hydraulic system. This tank serves as the storage container for the system's hydraulic oil or fluid. Understanding the importance, design considerations, and maintenance requirements of a hydraulic oil reservoir is essential for operators and engineers working with hydraulic equipment.

Types of Hydraulic Oil Tanks

  1. Rectangular Tanks
  2. Rectangular hydraulic oil tanks are the most common type, offering a simple and cost-effective solution for many applications. These tanks are typically made from welded steel or aluminum and can be customized to fit your specific requirements.

  3. Cylindrical Tanks
  4. Cylindrical tanks are another popular option, particularly for applications with limited floor space. These tanks can be oriented horizontally or vertically and are often used in mobile hydraulic systems, such as those found in construction equipment.

  5. Bladder Tanks
  6. Bladder tanks feature a flexible bladder inside the tank that separates the hydraulic fluid from the air or gas used to pressurize the system. This design helps to prevent fluid contamination and maintain consistent pressure.

Functions of a Hydraulic Oil Tank

The hydraulic tank performs several vital functions within a hydraulic system:

  • Oil Storage: The primary purpose of the reservoir is to hold a sufficient quantity of hydraulic oil to supply the system.
  • Heat Dissipation: As hydraulic fluid circulates through the system and components, it absorbs heat. The tank allows this heated fluid to cool before re-entering circulation.
  • Contaminant Settling: Contaminants like dirt and debris can collect in the fluid. The tank provides an area for these particles to settle at the bottom, away from the pump intake.
  • Air Separation: Hydraulic fluid can contain dissolved air, which negatively impacts system performance. The reservoir allows air bubbles to rise to the surface and dissipate.

Essential Hydraulic Oil Tank Features

When evaluating hydraulic oil tanks, look for these key features to ensure optimal performance and maintainability:

  • Baffles and Diffusers
  • Internal baffles and diffusers help to prevent fluid turbulence, aeration, and foaming. They also promote better heat dissipation and contaminant separation.

  • Filtration
  • Adequate filtration is essential for maintaining fluid cleanliness and preventing system damage. Look for tanks with built-in filter mounts or easy access for installing inline filters.

  • Inspection Covers and Cleanouts
  • Inspection covers and cleanout ports facilitate tank maintenance, allowing for easy fluid level monitoring and contaminant removal.

  • Sight Gauges and Level Indicators
  • Sight gauges and level indicators provide a visual means of monitoring fluid levels, helping to prevent system damage due to low fluid levels.

Sizing Your Hydraulic Oil Tank

Properly sizing your hydraulic oil tank is crucial for ensuring optimal system performance and longevity. Here are some factors to consider when determining the appropriate tank size:

System Flow Rate

The tank should be sized to hold at least three times the volume of fluid that the system pumps per minute. This allows for adequate fluid cooling and helps to prevent aeration.

Fluid Dwell Time

Dwell time refers to the amount of time the fluid spends in the tank before being recirculated. Longer dwell times allow for better heat dissipation and contaminant separation. Aim for a minimum dwell time of 1-2 minutes.

Expansion Space

Be sure to account for fluid expansion due to temperature changes. A good rule of thumb is to allow for an additional 10-15% of tank capacity for expansion.

Proper Hydraulic Fluid Selection

Choosing the right hydraulic oil for your system and ambient conditions is crucial. Fluid properties to consider include:

  • Viscosity: Select an oil viscosity that maintains adequate thickness across the operating temperature range.
  • Additive Package: Use a fluid with anti-wear, anti-corrosion, and antifoam additives suitable for your system's components.
  • Water Resistance: For environments prone to water contamination, consider a hydraulic fluid with good demulsibility to readily separate from water.

Always refer to the equipment manufacturer's fluid recommendations and follow a strict contamination control protocol when adding or changing hydraulic oil.

Hydraulic Tank Accessories and Options


Integrate high-efficiency filtration into the tank's return lines and breather to maintain fluid cleanliness. Suction strainers and in-tank or in-line filters are common.

Fluid Level & Temperature Monitoring

Visual level gauges, electronic level sensors, and temperature switches provide real-time monitoring of reservoir fluid. This allows early detection of leaks or abnormal operating conditions.

Tank Heaters

In cold ambient conditions, tank heaters maintain optimal fluid viscosity for start-up and operation. Immersion heaters or inline heating elements are typical.

Access Ports & Clean-out Covers

Manhole covers, access ports, and removable clean-out panels streamline tank cleaning, inspection, and maintenance procedures.

Hydraulic Tank Maintenance

Proper upkeep is critical to hydraulic system performance and component lifespan. Key maintenance points for the hydraulic oil reservoir include:

  • Regular Oil Changes: Drain and replace hydraulic fluid per manufacturer recommendations, typically every 2000 operating hours.
  • Cleaning: Periodically clean the tank interior to remove contaminant buildup, sludge, and varnish deposits.
  • Inspections: Routinely inspect for leaks, damage, or excessive fluid temperature. Use a sight gauge to monitor fluid level.
  • Breather Upkeep: Clean or replace tank breather filters to maintain proper air flow and keep out contaminants.