Liquid viscosity and pressure loss in hydraulic systems

During the use of hydraulic systems, the liquid has a certain viscosity, which inevitably leads to friction when the product flows in the pipeline. Therefore, the liquid in the hydraulic system inevitably loses a portion of its energy during the flow process, which is mainly manifested as pressure loss.

The pressure loss of the hydraulic system can effectively be divided into two types: loss along the hydraulic system and local loss. The loss along the equipment is the pressure loss caused by friction when the liquid flows through a straight pipe with a constant diameter for a certain distance.

Local losses in hydraulic systems are directly caused by sudden changes in the cross-sectional shape of the pipeline and changes in the direction of the fluid flow. Other forms of fluid flow resistance in the product can directly cause pressure losses, and the total pressure loss is equal to the sum of the loss along the route and local losses.

Due to the inevitable pressure loss in hydraulic systems, the rated pressure of the pump during operation is greater than the required working pressure for the system. Generally, the required working pressure for the system can be estimated by multiplying it by a coefficient of 1.3-1.5.

In a hydraulic system, each pressurized component has a relatively moving surface, such as the inner surface of its hydraulic cylinder and the outer surface of the piston. Due to their relative motion, there will be a certain gap between them. If one side of the gap is high-pressure oil and the other side is low-pressure oil, high-pressure oil will flow through the gap to the low-pressure area, causing leakage.

The flow loss of the hydraulic system affects the speed of movement, and leakage is also unavoidable. Therefore, the rated flow rate of the pump in the hydraulic system is slightly greater than the flow rate required for system operation.