Copyright Goodheart-Willcox Co., Inc. Chapter 8 Fluid Storage and Distribution 185 Other shapes and forms may also be used for hydraulic reservoirs. The cavities of large machine tools can be used as the reservoir. For example, the hollow structural members of equipment, such as the arms of front end loaders, may serve for both stor- age and fl uid transmission. In other mobile pieces of equipment, the oil used for the hydraulic system also functions as the lubricating oil for the transmission and gear train. In those situations, the transmission/ differential housing is, in a sense, serving as the system reservoir. See Figure 8-6. 8.1.4 Sizing the Reservoir It is often stated that a hydraulic system reservoir should have a storage capacity three times the rated fl ow of the pump (3:1). Although this is a very general statement, it has proved to be appropriate, especially in stationary industrial systems with typical actua- tor sizes. In any case, it is a good starting point when determining the size of a reservoir in a new or modi- fi ed system. In actuality, many factors must be considered when determining reservoir size. First, the reservoir must be large enough to store more than the anticipated maxi- mum volume of oil that will be returned to the reser- voir during any part of the system cycle. An example is the fl uid returned to the reservoir in a system contain- ing a single-acting cylinder with a large bore and long stroke. Other special considerations should involve the basic reservoir functions discussed earlier in the chapter. For example, an increase in the capacity of the reservoir increases the amount of time the fl uid is in characteristics, such as limited physical space or the need for positive pump inlet pressure, may require reservoir variations. L-shaped or overhead reservoirs may be used if a positive pressure (greater than atmospheric) is needed on the pump inlet line. Both of the designs place the pump below the level of the oil in the tank. See Figure 8-5. This difference in height may be only a few inches, but it allows gravity to assist in moving fl uid into the pump. Of course, these systems must have inlet line shutoff valves to minimize fl uid loss from the reservoir when the pump must be serviced. B A Cleanout plate Drain Filler/breather cap Filler/breather cap Pump/prime mover mounting pad Pump/prime mover mounting pad Goodheart-Willcox Publisher Figure 8-5. An L-shaped or overhead reservoir design is often used when the pump inlet line needs a slight positive pressure for more efficient operation. A—L-shaped reservoir. B—Overhead reservoir. Used with permission of CNH America LLC Figure 8-6. In some equipment using hydraulic power, machine cavities or transmission cases in conjunction with a constructed reservoir serve as the hydraulic system reservoir.