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Fluid power systems must have a sufficient and continuous supply of uncontaminated fluid to operate efficiently. The fluid must be kept free of all foreign matter. This reservoir guide covers hydraulic reservoirs. Information on various types of strainers and filters, and accumulators installed in fluid power systems will be added to this guide at a later date.
RESERVOIRS: A hydraulic system must have a reserve of fluid in addition to that contained in the pumps, actuators, pipes, and other components of the system. This reserve fluid must be readily available to make up losses of fluid from the system, to make up for compression of the fluid under pressure, and to compensate for the loss of volume as the fluid cools. This extra fluid is contained in a tank usually called a reservoir.
A reservoir may sometimes be referred to as a sump tank, service tank, operating tank, supply tank, or base tank. In addition to providing storage for the reserve fluid needed for the system, the reservoir acts as a radiator for dissipating heat from the fluid and as a settling tank where heavy particles of contamination may settle out of the fluid and remain harmlessly on the bottom until removed by cleaning or flushing of the reservoir. Also, the reservoir allows entrained air to separate from the fluid.
Most reservoirs have a capped opening for filling, an air vent, an oil level indicator or dip stick, a return line connection, a pump inlet or suction line connection, a drain line connection, and a drain plug. The inside of the reservoir generally will have baffles to prevent excessive sloshing of the fluid and to put a partition between the fluid return line and the pump suction or inlet line. The partition forces the returning fluid to travel farther around the tank before being drawn back into the active system through the pump inlet line. This aids in settling the contamination and separating the air from the fluid.
Large reservoirs are desirable for cooling. A large reservoir also reduces recirculation which helps settle contamination and separate air. As a ''thumb rule," the ideal reservoir should be two to three times the pump output per minute. However, due to space limitations in mobile systems, the benefits of a large reservoir may have to be sacrificed. But, they must be large enough to accommodate thermal expansion of the fluid and changes in fluid level due to system operation. Reservoirs are of two general types- nonpressurized and pressurized. Propower manufactures non-pressurized hydraulic reservoirs.
NONPRESSURIZED RESERVOIRS: Hydraulic systems designed to operate equipment at or near sea level are normally equipped with nonpressurized reservoirs. This includes the hydraulic systems of truck, factory, and ship installations. A typical reservoir for use with factory and ship installations is made of hot rolled steel plates and has welded seams, and is not generally suitable for mobile operation. The ends extend below the bottom of the reservoir and serve as supports. The bottom of the reservoir is convex, and a drain plug is incorporated at the lowest point.
Most nonpressurized reservoirs are constructed in a cylindrical shape. The outer housing is manufactured from a strong corrosion-resistant metal. Filter elements are normally installed internally within the reservoir to clean returning system hydraulic fluid. Reservoirs that are filled by pouring fluid directly into them have a filler (finger) strainer assembly installed in the filler well to strain out impurities as the fluid enters the reservoir. The quantity of fluid in the reservoir is indicated by either a glass tube, a directing gauge, or a float-type rod, which is visible through a transparent dome installed on the reservoir.
Please refer to the Wetline Systems Design and Operation section for issues related to proper hydraulic system engineering, operation and design.
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