Читать книгу Hydraulic Fluid Power - Andrea Vacca - Страница 49

The basic design of a hydraulic reservoir consists of a parallelepiped made of steel sheets. Small tanks (usually below 70 l) can be made of metal alloy or plastic. In a simplified cross‐sectional view, the tank appears as shown in Figure 2.19. The suction duct and the discharge duct are usually placed at the opposite ends to increase the residence time of the working fluid inside the tank. Separator septs or baffles are used to prevent a straight flow path between the discharge and the suction pipe. In this way the fluid is forced to travel a longer path with reduced speed. In many cases, the septs force the fluid to flow vertically within the reservoir so that the release of the undissolved air is promoted by gravity. The discharge pipe is usually well below the free surface level of the fluid. This helps in preventing splashing of the fluid and whirls that would increase foam and entrained air. The pipes are often cut with angles greater than 45°. At the discharge pipe this further promotes a smooth entering of the fluid in the tank; but most importantly, at the suction pipe, it allows for a gradual acceleration of the fluid within the pipe, thus reducing the entrance losses.

The figure also shows an air breather element, which should always be present to allow the air to enter or leave the tank as the level of the fluid varies to accommodate volume variations driven by accumulators or differential cylinders.

Other accessories typically present in hydraulic reservoirs, not shown in Figure 2.19, include inspection ports, level indicators, filling inlet port and drainage or discharge caps, internal de‐aeration separators (which are used to promote air separation and reduce foam), and magnets to capture contamination. The bottom of the tank is usually concave so that the solid impurities that remain at the bottom of the tank can be periodically drained through the discharge caps.

Figure 2.19 Typical design of a hydraulic reservoir.