Fluid Reservoir

Fluid Reservoir Requirements

The fluid reservoir of a hydraulic system is a rather plain and unexciting piece of equipment. Nonetheless, it is a very important part of the system. The main functions of the fluid reservoir in a hydraulic system include the following:

  

Accumulate and store an adequate supply of hydraulic fluid for the entire system at atmospheric pressure.

Break up any foam generated in the system, and separate dissolved air from the fluid.

Settle out heavy dirt particles, sludge, and water from the fluid.

Help cool the fluid and keep its operating temperature steady in the 100⁰ to 130⁰ F temperature range.

Provide a firm, accessible mounting platform for the pump, motor, intake filter, and other equipment in the power unit of the system.

The size of a reservoir is not given or classified by its physical dimensions, but by its liquid capacity. A reservoir should hold at least as such hydraulic fluid as the pump is capable of pumping in 3 minutes. This is usually enough to provide a stable fluid level and to operate the system efficiently. The oil level in the reservoir should never drop so low during operation as to expose the pump suction inlet or to let a whirlpool form. Each of these will draw air into the pump. If a pressure or return line breaks, the system must have enough fluid to come safely to a stop during an emergency shutdown. The capacity and approximate physical dimensions of commonly used rectangular reservoirs are given in Figure 4-1. The rectangular shape is widely used because it has low heat transfer, short cycling of the fluid, or reduced capacity or fabrication problems that circular, square, or narrow reservoirs have. However, in some applications space limitations may prohibit other reservoirs have to be used.  

As hydraulic fluid moves through the system collects dirt, wear particles, water, and gummy substances from the system.  When the fluid is returned to the reservoir, it should move through the reservoir as slowly as possible. The slow movement permits many of the contaminants that are suspended in the fluid to separate and settle to the bottom of the tank, forming what is called sludge. The larger the tank, the slower the movement of the fluid and the greater the amount of sludge

The bottom of the tank should be slightly V-shaped, and sloped toward one end, or have a low spot. A reservoir drainage valve should be installed in the sump to allow for sludge removal from time to time to time, or when the tank is cleaned out. A magnetic plug can be installed near the sump to collect small magnetic particles which otherwise might not settle out.