Hydraulic tank: Reservoir for the pressure medium

The hydraulic tank is the reservoir for the hydraulic fluid or the hydraulic medium of a hydraulic system. As a rule, this is a special mineral oil. The hydraulic tank only stores the oil, but otherwise keeps it pressureless. This is necessary to ensure that the tank can be filled or emptied safely at any time.

Position and function of the hydraulic tank

The hydraulic tank is a closed container connected to the surrounding air via vent valves. This connection is necessary so that pressure equalization can always take place in the tank. Returning oil would otherwise create overpressure, while outgoing oil would create negative pressure. Both could affect the pressure distribution in the hydraulic system, which is why pressure equalization in the hydraulic tank is very important. The tank is filled with oil through sealable openings. The oil flows from the tank first through a shut-off valve and immediately afterwards through a check valve. Only then is the hydraulic oil placed under the required operating pressure. The oil flows through the system in a closed circuit until it arrives back at the tank.

Extensions for large hydraulic tanks

Large hydraulic tanks, such as those used in heavy construction machinery, have a number of extensions and attachments. The following applications are typical for these uses:

• Coolers
• Sight glasses or electronic level sensors
• Safety valves
• Filters
• Sensors for quality monitoring

The hydraulic oil heats up significantly due to the actuators and, above all, the hydraulic pump. This heat accumulates in the tank and, if uncooled, can lead to the hydraulic oil boiling. Therefore, the oil is kept at its tolerable temperature by coolers and heat exchangers.

Sight glasses and level sensors inform the operator whether the oil supply is sufficient for the operation of the hydraulic system. In all hydraulic systems, the oil is filtered. These filters can be located at the outlet or the inlet of the tank. They filter out fine particles of abrasion or carbonization in the oil and ensure that these can no longer cause damage in the system.

Sensors for quality monitoring measure, for example, the electrical resistance in the tank. This allows conclusions to be drawn about the amount of metal particles in the hydraulic oil. This, in turn, indicates the onset of wear in the hydraulic system.

The complexity of the hydraulic tank therefore increases continuously with the size of the hydraulic system. This must be taken into account when planning hydraulic systems.