Hydraulic systems are used in a variety of applications to generate mechanical power. These systems typically employ a tank for holding a reservoir of hydraulic fluid or oil. Hydraulic fluid from the tank may be pumped to motors, cylinders, or other hydraulic devices. The volume of hydraulic fluid required by the hydraulic device may change during operation, and therefore hydraulic fluid is also returned to the tank.
Hydraulic fluid returning to the tank must often be reconditioned for reuse in the hydraulic system. First, the returning hydraulic fluid often has an elevated temperature that may be detrimental to the components used in the hydraulic system. Thus, the fluid may be cooled. Additionally, as the hydraulic devices are operated, the hydraulic fluid is placed under alternating high and low pressures that may cause air to become entrained in the fluid. Entrained air in the hydraulic fluid may cause cavitation and excessive noise as it cycles through the system, thereby accelerating component wear. Accordingly, it is often desirable to deaerate the hydraulic fluid in the tank, prior to reuse in the hydraulic system.
Practical constraints on tank size may limit the capacity for cooling and deaerating the hydraulic fluid. In general, larger tank sizes are preferred because they provide more surface area for exchanging heat to cool the fluid, and have additional space that may be used to reduce the fluid flow velocity, thereby to release air entrained in the hydraulic fluid. In many applications, however, only a limited amount of space is available for the tank. This is particularly true for mobile machines, where smaller tanks are used not only to meet the limited amount of available space but also to reduce weight and increase fuel efficiency.
The known tank designs that attempt to deaerate hydraulic fluid are overly large and complex. For example, U.S. Patent Application Publication No. 2003/0233942 to Konishi discloses a fluid tank having a built in cyclone device. The cyclone device is provided as part of a filter assembly that is disposed in a vertical pipe extending through the tank. The construction of the Konishi device, however, is complex to manufacture, requires a significant amount of vertical space, and is difficult to maintain.