The baffle and Air Sparation of Reservoir

Baffles

A baffle is placed to halve the reservoir along the long length, as in Figure 4-2. It should extend about two-thirds the distance from the bottom of the tank to the normal fluid level. The baffle is used to help circulate returning fluid around the inside of the tank, which allows it to give up some of its heat before entering the pump suction inlet pipe. With the return line and pump suction inlet located on the same end, as shown in Figure 4-3, the baffle keeps the fluid in contact with the outer surfaces of the tank for a longer period of time allowing a greater heat transfer. Some tanks have slightly different arrangements depending on the manufacturer and the application.

 
Air Separation 

When hydraulic fluid is under pressure it may contain a considerable amount of dissolved air. The dissolved air changes to foam in the return lines and is finally released in the reservoir. There must be enough space above the oil level in the reservoir to hold the foam until it breaks up allowing the escaping air bubbles a chance to be released. If not, the foam will overflow the tank and create a safety hazard.

Although Fig.  4-3 shows one return line, many systems have several return lines connecting to the reservoir. Almost all large return lines are connected to direction control valves (that supply fluid to the hydraulic actuators), relief valves, unloading valves, and other lines, which have high discharge rates. Small return lines are connected to the pilot flow control valves, pressure valves, and drainage or leakage lines that handle low volumes of fluid at atmospheric pressure. Return lines with high discharge rates are usually returned singly to the reservoir, while the smaller flows are sometimes connected to a common return line.

Most of the large return lines discharge into the reservoir below the oil level at a point about 1 inch above the bottom. This prevents the fluid from entraining or absorbing air as it leaves the return line. Return lines containing large amounts of air or foam in the fluid discharge above the fluid level onto a sloping plate placed at a 5⁰ to 10⁰ angle from the horizontal as shown in Fig. 4-4. This plate spreads out the fluid letting the air release faster. It is also important that drainage and leakage lines at atmospheric pressure discharge above the fluid to prevent an airlock (trapped air) from foaming.

Large amounts of foam in the return lines, or in the reservoir near the return lines, can usually be removed by placing a slanted screen in the reservoir. The screen is usually about 60 mesh, and is mounted below the surface of the liquid near the return lines at an angle of 30⁰ from the horizontal. Foam trying to pass through the screen will give up its air to the atmosphere.