Hydraulic Reservoirs – The Ultimate Guide

Hydraulic Reservoirs

Hydraulic systems require reservoirs to properly function. The hydraulic reservoirs are essential, especially to systems that involve liquid levels that fluctuate throughout operations. Systems with this component can be used for a variety of applications.

What are Hydraulic Reservoirs?

The hydraulic reservoir is a storage chamber designed for the main function of containing the hydraulic fluid.

This fluid is an essential component that performs several functions throughout the system. This container layout incorporates an allowance to withstand fluid expansion while allowing air to escape and facilitating the cooling of the liquid.

Hydraulic Reservoir
Hydraulic Reservoir

Function of Hydraulic Reservoirs

The hydraulic reservoirs are designed to perform several functions. These functions include;

  • These storage facilities are designed for the primary function of containing the hydraulic fluid that is required by the systems. It is optimally positioned in the system near the pump inlet that draws the liquid as required during operations.
  • The reservoirs can also cool the liquid through dissipation of heat as well as conditioning the fluid. Conditioning occurs as foreign matter settles down and the large surface helps dissipate the heat.
  • As operations reach their peak levels heat is generated that causes the heated liquid to expand. The reservoir is designed to contain expanding fluids and the liquid that drains back when the system is no longer operational.
  • The reservoirs are designed with an inbuilt internal baffle. This component is incorporated into the design to assist with the circulation of turbulent fluid originating from the return side ending up at the cooler pump inlet. This provides required ample time for any contaminants present in the fluid to settle down.
  • The storage compartment also serves other functions not related to containing liquid such as providing a surface for mounting other components. Given its large surface area, it can provide an attachment location for parts like accumulators, electrical control panels, motor filters, and manifolds.

Sizing Hydraulic Reservoirs

There are a few factors that you should take into consideration when selecting the most suitable for your systems. The type of application going to be undertaken by your system is one of the factors as it will be the determining feature when it comes to the requirements. Mobile applications for example require about twice as much pump flow rate.

Other factors include the flow of your pumps, a suitable reservoir needs to be at least 2.5 more than the flow of the pumps. This is essential as it provides enough storage space for the fluid. Return flow and supplementary accessories should also be factored in when selecting the size. Although larger reservoirs have added benefits including heat dissipation and enhanced settling, you should get a size that is practical and will fit seamlessly into your systems

Configuring Hydraulic Reservoir

Configuration is important to ensure that the hydraulic reservoir functions optimally and efficiently. Some factors should be considered when undertaking this task. These factors include;

  • Orientation of the pump is a key factor with typical reservoirs adopting a V-shaped bottom tank that has a horizontally mounted pump on its cover. An alternative position involves the motor and pump placed below the hydraulic reservoir.
  • One of the main accessories incorporated into these storage containers is heat exchangers that aid in the dissipation of heat. The location of the storage is essential for this function as it requires a position with access to free airflow to facilitate the cooling process.
  • There are different types of hydraulic fluids and the type of fluid is a determining feature in the most suitable design. Some varieties of oil fluid require a flooded suction which has other advantages including increasing the service life of the pump while minimizing cavitation.
  • Another important feature to consider is the configuration of the inlet pump as the different varieties can affect the longevity of the part.
  • The design selected and its position should be simple and accessible. This is to enable easy maintenance and servicing of the storage chamber. It should incorporate a fill opening along with drain connections which ideally should be located at the bottom. A level gauge is also an essential additional feature.

Components of Hydraulic Reservoirs

There are different types and configurations of hydraulic reservoirs and as such there are varying components. General components of hydraulic reservoirs include;

  • Fluid Storage chamber: This is the area where the fluid is contained. It also allows contaminants to settle to the bottom and
  • Heat exchangers; Assist with the dissipation of heat.
  • Mounting Surface: External surface area that is typically used to mount other components.
  • Air breather: Provides an outlet for air to separate from the fluid.
  • Baffle Plate: This section forms a barrier between the suction chamber and the return chamber.
  • Return chamber: This part contains the fluid that reverts when the system is no longer in use.
  • Suction chamber: This section contains fluid drawn from the reservoir.
  • Filler Opening: an opening into the tank that performs functions including letting air out, temperature control, and refilling the fluid into the tank.
  • Drain Plug: Use to drain out fluid from the storage chamber.
Hydraulic Reservoir Components
Hydraulic Reservoir Components

Function of Reservoir Accessories in Hydraulic Systems

Some of the general accessories incorporated into the hydraulic reservoir to streamline its functions include;

  • Strainers and Filters: used to filter out any contaminants that find their way into the fluid through the system.
  • Visual Fluid Level switch; This helps to visually determine the fluid level in the chamber and is equipped with sensors that alert you when levels are low.
  • Temperature Gauge: Assists in keeping track of the temperature of the fluid present and has the ability to issue an alert when temperatures get too high.
  • Air Breather; provides an outlet for air separated from the fluid and is capped to prevent possible contaminations
  • Clean-Out Cover: A cover designated to provide access to the reservoir for maintenance.
  • Magnet Rod Assembly: for separating any metals present in the fluid

Vented vs Pressurized Reservoirs

Although both reservoirs are designed for the same purposes the two varieties are equipped with varying features and as such function differently. The differences between vented and pressurized reservoirs include;

  • Vented reservoirs are designed with an exposed vent line that exposes them to atmospheric pressure. These systems are therefore fitted with filters to prevent contaminants from the air from getting into the system. On the other hand, pressurized reservoirs are closed systems that are closed off from the atmosphere
  • With vented reservoirs, the vent line is designed to suction into and release air out of the reservoirs. They are typically incorporated into systems for industrial applications that are stationary and environments with average atmospheric pressure. For pressurized systems air is manipulated using the help of an engine or using hydraulic pressure.
Pressurized Hydraulic Reservoir
Pressurized Hydraulic Reservoir

How to Maintain Reservoirs in Hydraulic Systems

It is important to properly maintain your hydraulic system reservoirs to lengthen its lifespan and ensure its functions optimally. Here are some steps you can employ when maintaining your hydraulic reservoirs

  • You should drain older fluid and then clean the storage before refilling it with fresh fluid. It is important to turn off all the systems when doing this and release the fluid while it is still warm.
  • Set up a regular schedule for your maintenance to ensure that it continues to function effectively. General maintenance should be regularly carried out to ensure avoid potential damages caused by the build of contaminants and heat among others.
  • You should replace the media used for filtering when required. You should also constantly monitor the media to ensure that debris does not build up and clog the filter. The air intake should also be regularly cleaned out to keep it open and free of any contaminants
  • It is important to regularly monitor fluid levels and temperature and ensure that they are at their recommended levels. This can be done by installing switches that will function as alarm systems that will alert you when the levels get too low or the temperatures get too high.
  • When refilling the tank, it is important to first clean out the previous fluid to prevent oils with different compositions from mixing. Mixing different types of oils may result in potential problems.
  • Regularly inspect the drain plug and ensure that is coated to make it and other internal surfaces corrosion-resistant to prevent it from corroding into the fluid.

How to Choose Hydraulic Tank Reservoir

When selecting a tank reservoir, you should consider the following factors;

  • You should select the most suitable size which varies according to the type of application that is to be utilized. The easiest way is to upsize the tank to ensure that it holds two and a half times the capacity of the pump.
  • The design should consider all your requirements as well as the system’s needs. Some factors included in the design include the pressure of the suction head and simplicity in terms of maintenance.
  • There are two main configurations of these tanks which are the vented systems and pressurized systems. You should select the one best suited for the application. Vented systems rely on atmospheric pressure and are therefore open while pressurized systems are closed and rely on motorized pressure.
  • Ensure that the reservoir contains the required accessories and supplementary features required by your applications.
  • The construction material is also important as it may influence various functions. Welded steel plates are the recommended material.
Hydraulic Reservoirs
Hydraulic Reservoirs


It is important to know and understand all the necessary features that are incorporated into the different types of hydraulic reservoirs. This insight will help you to select a reservoir that is most suitable for your unique applications.

More Resources:

Reservoir Systems for Hydraulic Equipment – Source: Power and Motion

Hydraulic Oil – Source: Target Hydraulics

Hydraulic Systems Parts – Source: Target Hydraulics

Types of Hydraulic Systems – Source: Target Hydraulics

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