Hydraulic Reservoir | Functions | Layouts | Uses

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What Is A Hydraulic Reservoir?

The hydraulic reservoir can be thought of as a container that is capable of holding the fluid required by the system. It also includes a reserve to cover any kind of losses from minor leakage and evaporation. The reservoir can be made mainly to provide space for the expansion of the fluid, permit air entrained in the fluid to escape and to help in cooling the fluid.

Hydraulic Reservoir
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Why Is Hydraulic Reservoir Required?

Hydraulic systems always require a finite quantity of fluid usually liquid, that should be stored and reused continually as the systems keep on working. Thus, part of a hydraulic reservoir or tank is a very important part of hydraulic systems. This reservoir or tank may be a part of the framework of the main machine or maybe a  separate stand-alone unit. In both cases, the design of the reservoir and implementation plays an important role.

Poor tank design can greatly reduce the efficiency of a well-designed hydraulic system. A hydraulic reservoir does not only provide a place to put fluid, but it also does much more than that. A well-designed reservoir is also used to dissipate excess heat energy, allow time for contamination to drop out of the fluid, and allow air bubbles to come to the surface and dissipate out of the fluid. It might give a positive pressure to the inlet of the pump and makes a convenient mounting place for the pump and its motor, and valves.

Also Read:  Is My Transmission Fluid Leaking From Bellhousing? [Diagnosis And Fixes]

Standard Layouts Of Hydraulic Reservoirs:

  1. Pump on top: This layout is a really common reservoir/pump layout and is used by a number of suppliers. The top surface, which is flat, of a standard reservoir, is a perfect place to mount the pump and motor.
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The main condition for this configuration is that the pump must create a vacuum which is enough to increase as well as accelerate the fluid into the inlet of the pump. For most of the reservoirs or pumps, this is not really a big problem, however, it is not the best situation for any reservoir. The piping done in this layout should be sealed, must be as short as it can be made, and have very few or no bends.

2. Pump alongside tank: This design can be considered satisfactory for any type of reservoir. A lot of suppliers prefer this configuration. This layout is sometimes known as a flooded suction, mainly because the pump inlet is always filled with fluid.

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Although the inlet of the pump always has fluid in it, this creates some vacuum in the line of the inlet when the reservoir is running. A reservoir or pump with its inlet below the level of the fluid no longer has to raise the fluid, but it does have to accelerate and move it. But, this design is considered far better than the pump on top layout and can extend the service life of any type of configuration of the tank.

3. Pump under tank: This design places the pump below the reservoir to take the benefit of static head pressure. There is always some pressure at the bottom of any fluid column. With the tank placed above, the pump not only consists of fluid at its inlet all the time, but this fluid also can be at 2- to 4-psi positive pressure.

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This configuration can prove to be difficult to work on without enough headroom for the mechanic.

Accessories Of The Hydraulic Reservoir:

No matter what is the size or style of the reservoir being used, it is always suggested that some or all of these commonly used accessories are included in the construction of the reservoir:

  • Visual fluid level/temperature gauge
  • Air breather/filler cap assembly
  • Clean-out cover (bolt-down top)
  • Fluid level switch
  • Fluid temperature switch
  • Magnet rod assembly
  • Fluid drain/sampling valve
  • Corrosion-resistant interior coating

Maintenance Of The Hydraulic Reservoir:

All industrial hydraulic systems must include the need for pressure line filters, return line filters and reservoir air breathers in order to decrease the number of contaminants of fluid entering the tank. Some systems must also incorporate suction strainers or some filters. Filter indicators or switches and a maintenance schedule must be included to make sure that the dirty filter elements are replaced timely. Lastly, it is always suggested that the reservoir be drained and the inside portion is cleaned at least once a year.

Functions Of The Tank In The Hydraulic Reservoir:

The main cause that the reservoir is installed is to store fluid. The universally accepted rule for sizing a tank is that the volume of the tank should be two to four times the flow of the pump in GPM. This is only a basic rule. Some systems might have a requirement of somewhat more volume, while less fluid might be enough for some other systems. A 25-GPM pump would work well with a 50- to 75-gallon reservoir for most of the systems.

With this basic rule being applied, the returned fluid, according to theory will have two to three minutes in the tank before its circulation again. A baffle separates the return line from the pump inlet line which forces the fluid to take the longest path which is possible, through the reservoir before returning to the inlet of the pump. This configuration also mixes the fluid very well and also provides more time to drop the materials which contaminate and even time to get de-aerated. Moreover, the fluid will spend a lot of time remaining in contact with the outer walls of the reservoir to dissipate excessive heat.


After reading this article, you will be able to understand different layouts in which hydraulic reservoirs can be found and the pros as well as cons of different configurations. The function and importance of the hydraulic reservoir will also be clear to you I hope.

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